2003 AES Annual Meeting Abstracts

Distribution, abundance and reproductive biology of the blue shark Prionace glauca in the Southeastern Pacific Ocean

Prionace glauca a is a cosmopolitan oceanic species fairly well known in most oceans, however there is a lack of information about its distribution, abundance and reproductive biology in the Southeastern Pacific off Chile. In order to determine the distribution, abundance and reproductive cycle of the blue shark in the Southeastern Pacific off Chile, a sampling program was conducted onboard artisanal and industrial longline boats that operate in international waters off the Chilean EEZ. The study period was between November 2000 and August 2001 and the study area covered from 24° 07¢ S to 37° 13¢ S, off the Chilean coast. The sex proportion showed a dominance of males in the captures, which is coincident with the spatial sexual segregation hypothesis proven in several world oceans. A macroscopic sexual maturity scale was developed using the onboard experience, finding sexually mature female specimens with offspring and spent in over 145 cm TL sizes. Considering the external morphological male sexual characteristics, the best maturity indicator was the clasper texture, being the largest percentage of mature specimens found at sizes of 195 cm TL or over. The birth period in the study area was determined to be between July and November, being 52 cm TL the birth size. The mean fecundity was determined to be 33 offspring, with a range between 3 y 62 offspring per female. Our findings are compared with those of other studies in other oceanic areas. Financed by Fisheries Research Fund, Chile, (Proyecto FIP 2000-23).

Trophic ecology of scalloped hammerhead juvenile (Sphyrna lewini) in the Gulf of California

The scalloped hammerhead shark Sphyrna lewini is one of the most important species caught in Mexican waters. We describe the feeding habits and evaluate the trophic level of Sphyrna lewini in the southern Gulf of California. The scalloped hammerhead shark is caught by fisherman in the SW of the Gulf of California. The methods used were: the Index of Relative Importance (IRI), Prey species diversity (Index of Shannon-Wiener), diet breadth (Levin’s standardized Index), dietary overlap by sexes and size (Morisita-Horn Index), and stable carbon (13 C/12 C = d13 C) and nitrogen (15 N/14 N = d15 N) isotopic analysis. A total of 139 stomachs of scalloped hammerhead sharks were analyzed. According to the IRI, the juveniles of scalloped hammerhead feed mainly on demersal and epipelagic fish (Scomber japonicus, Synodus evermanni, Sardinops caeruleus, Auxis thazard) and mesopelagic cephalopods (Dosidicus gigas, Abraliopsis affinis, Onychoteuthis banksii). The diversity of prey species and diet breadth are relatively low 5 (H¢ = 2.74 and BI = 0.16). These results indicate that scalloped hammerhead shark is a specialist predator considering their preference on few prey species. A significant overlap between sexes was found (Cl = 0.76). The recorded lengths were lower than 150 cm, therefore they are considered juvenile aggregations and have a dietary overlap among age-groups between 87 and 110 cm and between 119 and 142 cm. The stable carbon and nitrogen isotopic analyses shown that juveniles have a higher trophic position than adults of this species. No difference in the trophic position was observed between sexes. Bahia de La Paz is believed to be the Sphyrna lewini nursery zone.

Estimation of population parameters for the blue shark (Prionace glauca) in the North Atlantic from mark-recapture analysis

Blue sharks are an important part of the by-catch in international tuna and swordfish fisheries in the North Atlantic. The multifleet logbooks available with fishery data are not considered to be complete given the large number of incidental captures, variation in release status (alive vs. dead) and unreported captures over time. Thus these data are not suitable for stock assessment and population modeling. Furthermore, stock assessment analysis of a highly migratory species such as the blue shark is difficult at best. The complex sexual and life-stage segregation patterns of the population in the North Atlantic make the modeling process even more difficult. Alternative methods are needed to deal with the problem. We use the tag-recapture database (1962-2001) of the National Marine Fisheries Service (NMFS) Cooperative Shark Tagging Program (CSTP) to derive population parameters for the blue shark in the North Atlantic. Our 6 approach is based upon the use of GIS software for data management, mapping and spatial analysis. Estimates of survival by life-stage and sex are also being developed relative to both spatial and temporal patterns. The potential use of these parameters in future population modeling studies is discussed.

Evolutionary origins of lymphocytes: mapping emergence of T-cell and B-cell transcriptional networks in early vertebrates

The evolutionary origins of lymphocytes can be traced by phylogenetic comparisons of key genetic features. Homologs of rearranging T-cell receptor and immunoglobulin (B-cell) receptor genes have not been identified in any extant life form more phylogenetically primitive than cartilaginous fish, even though homologs of transcription factor genes essential for the 17 development of T-cells and B-cells are present throughout all vertebrate and most invertebrate groups. Examination of gene sequences, gene duplication, orthology, and conservation of DNA binding domains for transcription factor genes can help define the emergence of lymphocytes early in vertebrate evolution. Using a representative elasmobranch, the clearnose skate, Raja eglanteria, homologs of transcription factor gene families, including GATA-3, EBF-1, and various PU.1 and Ikaros family members have been identified and have been shown by sequence similarity and domain structure to be orthologous to higher vertebrate counterparts, including mammals. Structurally, these factors show high homology to their mammalian counterparts in every known functional domain. Co-expression of transcription factors and antigen receptors within specific tissues indicates conserved use of T-cell versus B-cell factors. One striking difference from mammals is an unexpected divergence in the use of certain B-cell factors into separate tissues. The results indicate that portions of the gene regulatory networks that operate in mammalian T-cell and B-cell development were present in the common ancestor of.mammals and cartilaginous fish, at the time that rearranging antigen receptors emerged.

Age and growth in Scalloped hammerhead Sphyrna lewini juveniles caught in the Lower Gulf of California

The sharks have a late age growth, low fecundity, long gestation period and slow corporal growth. therefore, it is necessary to know basic biological aspects such as age and growth for a management of this fishery in Mexico. The results of age and growth rate from Scalloped hammerhead Sphyrna lewini are shown. The sampling area was the Gulf of California. One hundred seventy organisms (82 males and 88 females) have been collected and 116 vertebraes were obtained. The technique applied was resine and transversal cuts. Growth bands were observed with a video monitor VW 5490. In the length frecuency analysis, a size range was found, which varies from 79 cm to 293 cm total length. There is no differences in the relationship vertebrae ratio-total length by sexes (y=13.024+45.618x in males and y=13.635+42.969x in females). The age of 62 organisms was determined (34 females and 28 males) and 54 showed opaque border and 8 hyaline border. The age groups were obtained were from 0 to 2, according to the hyaline borders number. The youngest juveniles with a cero age had 141 cm total length in the largest female and 116 cm in males. The group 1 with a total length of 116 cm in males and 151 in females. In the group 2, the largest male showed 112 cm and 162 cm in females. Each annulus represents 6 months, so the age for the first group was 6 months, the age for the second group was one and the age for the third group was one and a half year._

Coming-of-age of shark stock assessment: decision analysis using a Bayesian age-and sex-structured model incorporating multiple fleets and spatial dynamics, and applied to the sandbar shark fishery of the U.S.

The assessment and management of sharks and rays lagged behind that of teleost species for decades. But recent worldwide concern over the conservation and management of elasmobranchs has followed mostly-unchecked increases in their exploitation in the face of stock depletion. Methods for the stock assessment of sharks have thus received renewed attention and have improved substantially over the last ten years. We present here a sophisticated state-of-the-art stock assessment model applied to the US Atlantic Coast sandbar shark (Carcharhinus plumbeus) fishery. This is an age- and sex-structured, fleet-disaggregated model that simulates the dynamics of the shark population and the fisheries, taking into account specific characteristics of shark biology. The simulated population is assumed to occupy two areas (the area in the U.S. EEZ and the Mexican part of the Gulf of Mexico) and to have age- and sex-specific movement between them. Bayesian statistical methods are applied to fit the model to the data and deal with the uncertainty in model parameters and assumptions. The model is used to investigate the effects of different assumptions for spatial/temporal distribution of fish on predictions of shark abundance and yield. Taking into account these assumptions, we apply a decision analysis to evaluate the potential consequences of different management measures on future stock size and catches.

Freshwater stingray conservation program at Amazonas State, Brazil

The neotropical stingray family Potamotrygonidae is the only Elasmobranch group in which all members live in freshwater environments. Freshwater stingrays have the same life-cycle limitations of marine forms, in additional to their environmental limitations. It is these environmental limitations that have brought the fish into closer contact with humans, and has produced in a stronger antagonism between fish and people. Much of this antagonism stems from the injury caused by the sting, which results in a serious infection To avoid accidents, riverine people often mutilate or kill freshwater stingrays. In the last decade, however, the exotic colors of these species have made them popular.attractions in public aquariums and among fish hobbyists. Their importance as ornamental fish has grown to the point that 23.500 freshwater stingrays are now exported annually from Manaus. At least five species are represented in this trade: Potamotrygon motoro, Potamotrygon orbignyi, Potamotrygon schroederi, Paratrygon aiereba and a yet undescribed species of Potamotrygon. To regulate the ornamental fishery in freshwater stingrays, an export quota was developed for the species that represent 25 most exports (Law n0 . 22/98; IBAMA 1998). The ornamental fish industry has assumed the responsibility for the conservation program of freshwater stingrays. This program is considering not only the action of ornamental fishermen on the populations, but also the changes in their environment and the impact of the negative fishery used to reduce populations around centers of human activity.

A review of shark fisheries in Central America; species composition, historical catch and fishing effort data, and management issues

Shark fisheries in Central America have taken place in coastal waters for decades. By the late 70s, these fisheries were showing signs of overfishing. Longline fisheries were introduced in Costa Rica in 1982, and by 1988 the fleet included over 500 vessels. Costa Rica allows the landing of shark products from international longline fleets (over 100 vessels) with no control. Piracy is a common problem, as well as landing of fins alone, against Costa Rica regulations that demand fins attached. Shark fins from this industry are exported to Taiwan. Carcasses are exported to El Salvador and Guatemala, for processing of steaks and export to Mexico. Local fishermen of these countries can no longer supply the market. Catch rates of sharks during longline operations in the EEZs of Costa Rica and Nicaragua during the last 10 years are examined, including catch data from an ongoing project. Management recommendations to mitigate impact are closures, limit landing operations of international fleets and initiate reporting by international and national fleets alike, evaluate use of off set circle hooks, blue bate die and dehookers, and provide funding for education of fishermen programs.

A new species of lantern shark (Chondrichthyes, Etmopteridae, Etmopterus) from the eastern Pacific off Central America

We report on a new lantern shark belonging to a group of larger Etmopterus species that includes the nominal species E. baxteri, E. granulosus, and E. princeps. These species and the unrelated, but superficially similar, E. unicolor lack well defined patterns of color indicating photophore masses or have these patterns obscure as adults. These are the deepest dwelling species of Etmopterus, generally occupying depths greater than 1000 m. Two specimens of Etmopterus sp. caught in the eastern Pacific were analyzed along with ontogenetic series of E. baxteri, E. granulosus and E. princeps by the use of principal component and discriminant function analyses of morphometric characters. The statistical analyses were successful in classifying the measured specimens into three distinct groups, allowing us to recognize the two specimens as members of a new species. In addition, it verifies the placement of E. baxteri in the synonymy of E. granulosus, a view previously reached by Tachikawa et al. (1989). The complete description of the new species, as well as a discussion of the characters used by the analyses to separate the three taxa, is presented.

Feeding habits of the dominant ray species in the Almejas Bay (B.C.S., Mexico) artisanal fishery

Rays are one of the most abundant and ubiquitous groups of fishes in tropical and subtropical marine nearshore environments, where they often occupy high trophic levels. Global fishing pressure has increased on rays, typically without regulations or catch records. In Almejas Bay, Baja California Sur, an artisanal ray fishery operates primarily from April through August. Sampling of rays from this fishery for diet composition was conducted at Puerto Viejo, in June 1998-2000 (20 days, 34 vessel trips) and August 1998-1999 (35 days, 92 vessel trips), with 62 supplemental samples collected in 2001 and 2002. Of 4,035 elasmobranchs landed among at least 22 species, four species (Rhinobatos productus, Dasyatis dipterura, Narcine entemedor, and Gymnura marmorata) comprised 91.7% of the catch. Sex ratios, length frequencies, CPUEs (number/vessel) and a description of the fishery will be presented. This fishery peaked in June (total CPUE = 42.74), targeting mainly gravid female R. productus (CPUE = 21.48) and N. entemedor (CPUE = 10.74). In August, the fishery operated at a diminished capacity (total CPUE = 22.30), subsisting primarily on resident populations of D. dipterura (CPUE = 9.46) and G. marmorata (CPUE = 4.74). Stomachs and foreguts excised, preserved, and examined from 2,184 total specimens provided data on ontogenetic, intergender, and interannual differences in diet and facilitated comparisons of dietary overlap. Rhinobatos productus preyed primarily on crustaceans (shrimp and crabs) and, to a lesser extent, polychaetes with fishes also taken by large specimens. All sizes of G. marmorata consumed exclusively teleost fishes with a single occurrence of a squid. The diet of D. dipterura consisted mainly of epibenthic and infaunal invertebrates, including pea crabs, small bivalves, and polychaetes. Narcine entemedor fed primarily on polychaetes, sea slugs, and eels. The diets of these species did not exhibit a high degree of overlap, potential facilitating their coexistence.

Information for ecological risk assessment of piked spurdog (Squalus megalops) off southeastern Australia

The life-history traits of the Australian population(s) of the piked spurdog (Squalus megalops) are being determined and available data on catch history, distribution and gillnet selectivity are being collated and analyzed. As part of a quantitative ecological risk assessment of the chondrichthyan fauna, essential information on the reproductive biology, the age and growth, and the dietary composition of this shark species is being recorded from samples obtained from southeastern Australia. The data will be used to determine the ogives of the onset of maturity and of breeding and maternity as a function of length and age of shark, estimate the gestation period and reproductive cycle, determine the fecundity of females, and estimate their biological productivity. The growth rate and maximum age of each sex and the feeding habits and ecological role will also be determined. This study aims to gain knowledge of the basic biology and to provide the data and parameter inputs to models for ecological risk assessment, IUCN red list assessment, and management and conservation of this species.

Maternal investment of thyroid hormones in the embryonic bonnethead shark, Sphyrna tiburo

The normal development of vertebrates depends on the presence of thyroid hormone (TH). TH influences the basal metabolic rate, differentiation of the central nervous system, skeletal and somatic growth, and sexual maturation. The presence of TH has been detected in the egg yolk of teleost fish and has been shown to positively influence growth and survivorship of offspring. This study verifies the presence and concentration of TH in the egg yolk of the placental viviparous Bonnethead shark, Sphyrna tiburo. Sharks were collected from three sites along the Florida gulf coast. TH in shark yolk and maternal serum are quantified by use of radioimmunoassay (RIA). In addition, the thyroid gland of the embryonic shark is examined histologically for the endogenous production of TH.

Site fidelity and residency periods of white sharks at certain pinniped colonies in South Australia

White sharks (Carcharodon carcharias) are listed as vulnerable in Australia and are protected in all State and Commonwealth waters. While generally uncommon, there are areas (sites) where white sharks aggregate or where individuals frequently revisit. These include pinniped colonies that are prime feeding areas for adult and sub-adult animals and are likely important habitat for them. Despite the protective legislation, there is still little firm knowledge of how best to make such protection effective. Methods of reducing by-catch in commercial fisheries, identification of critical habitat, the potential effectiveness of protected areas and the effects of ecotourism viewing of white sharks around pinniped colonies are critical issues for the effective protection and management of white shark populations in Australian waters. There is a need to understand critical habitat areas, in terms of residency periods and site fidelity, in developing threat abatement plans for the species. Automated acoustic listening stations moored on the bottom at the North and South Neptune Islands, and Dangerous Reef were used to examine residency periods and site fidelity at these pinniped colonies. Twenty eight acoustically tagged sharks were monitored over a 500 day period. One of these sites is used regularly by ecotourist operators and we examined the effects of repeated chumming on white shark movements and behaviour.

Site fidelity, residency times and activity space in grey nurse sharks in eastern Australia

Grey nurse sharks (Carcharias taurus) are considered to be critically endangered on the east coast of Australia with diver surveys suggesting their numbers are at all contemporary-time low levels. During certain seasons, grey nurse sharks aggregate at selected rocky reefs on the east coast of Queensland and New South Wales. At this time diver observations suggest the sharks spend much of their time around the caves and gutters of these aggregation sites. To afford greater protection to this species, more information is required on the species daily activity space around the aggregation sites. We used bottom-moored acoustic listening stations to monitor the residency periods of acoustically tagged sharks at sites in New South Wales and southern Queensland. We actively tracked sharks at the same sites to examine their diurnal movement patterns and swimming depth. The sharks tended to be more active at night, moving around the reef areas and in some cases they traveled over 1 km away from their daytime gutters. While swimming depths were generally within a few metres of the bottom, some individuals that moved away from their daytime sites swam for periods in mid-water some 15- 30 m above the bottom. The offshore excursions and mid-water activity may be related to hunting.

Temporal reductions in the distribution and abundance of U.S. Atlantic sawfishes (Pristis spp.)

The smalltooth sawfish (Pristis pectinata) and the largetooth sawfish (Pristis perotteti) are tropical marine and estuarine animals that have the northwestern termini of their Atlantic ranges in the waters of the eastern United States. We present a chronology of over 400 verified records of Pristis spp. from the U.S. between the years 1782-2002. P. perotteti has always been very rare in U.S. waters, verification of its presence being limited to a total of 13 collections from Texas, Florida, and Alabama. P. pectinata was historically more widespread and common, with captures ranging from Texas to New York. Warm water temperatures, apparently higher than 15-18°C, are required by this species. As a result, records of P. pectinata from areas north of Florida have been largely limited to spring and summer periods when inshore water temperatures reach these temperatures. Southern Florida apparently has a year-round resident population, portions of which may have been involved in northward migrations in the spring and summer, and southerly return movements in the fall. There has been a marked contraction of range of P. pectinata along the Middle and South Atlantic bights over the past century, with only one sawfish being captured north of Florida since 1958. The fact that documented sawfish catch records have declined during this period despite tremendous increases in nearshore fishing effort underscores the demise of U.S. Pristis spp. populations.

Trophic ecology of the silky shark Carcharhinus falciformis in Baja California Sur

Stomach contents of 264 silky sharks were analyzed. The sharks were caught in Punta Lobos (PL) and Punta Belcher (PB), located in the west coast of Baja California Sur, during summer and fall 2000- 2002. Sixty six percent of all sharks contained food in their stomachs. In PL the jumbo squid Dosidicus gigas was the main prey species (30.5% of Index of relative importance), whereas the red crab Pleuroncodes planipes (44.5% IRI) was in PB. Using the width breadth (Levins Index) and diversity index (Shannon-Wiener), the silky shark is a specialist feeder in both areas, because predate mainly in three species (red crab, jumbo squid and jack mackerel). We found a trophic overlap (Morisita-Horn index) between sexes and between juveniles and adult males.

Can ecosystem models be used to assess the impacts of fishing on shark populations?

Apex predators, like sharks, in marine ecosystems may play a key role in determining food web structure. The exploitation of sharks by fisheries could therefore have large effects on ecosystems by.selectively harvesting apex predators. A multispecies ecosystem model using the Ecopath/Ecosim software was developed for the southeast United States and Gulf of Mexico. Models incorporated time series estimates of biomass, fishing mortality, and bycatch rates were used to evaluate the relative contributions of fishing on shark populations and ecosystem dynamics. Preliminary evidence suggests that direct harvesting of sharks by longline fisheries had insignificant trophic impacts. Recreational harvests on bull sharks caused a slight increase in juvenile shark populations but had little effect on other components of the ecosystem. However, increases in the bycatch of juvenile sharks and other species by shrimp trawls caused 90 profound effects on food webs. Various management scenarios such as closed areas and marine protected areas were also investigated.

Reproduction of blue shark, Prionace glauca, in the western coast of Baja California Sur, Mexico

The blue shark Prionace glauca is the most abundant shark species in the Baja California waters. It is found all year in the western coast of Baja California Sur. Samples were obtained in the fishing camps of Punta Belcher and Punta Lobos in Baja California Sur, from August 2000 to February 2003. Measurements of reproductive organs, claspers length, length and width of the oviducal gland, and diameter of the biggest oocyte for the determination of the sexual maturity in males and females were used. 974 blue sharks, 627 males and 347 females have been sampled. The biggest abundance was in winter and spring, associated to lowest water temperatures. Males ranged from 81 cm to 270 cm TL; whereas females were from 90 cm to 252 cm. Sex ratio in adults was 2M:1H, which suggests a sex segregation when they reach maturity; whereas in embryos the sex ratio was 1M:1H. Size of first maturity for males is 180 cm TL, and 92 185 cm for females. Most of the juvenile males were found during winter and spring; whereas adults were found in summer. We recorded 35 pregnant females with 33 to 40 embryos in average with different development phases. Size range for pregnant females was 185 cm to 252 cm TL. We did histological analysis, including spermatogenesis in males, and sperm storage in the oviducal glands of females.

Age and growth determination of a deep-sea squaloid shark, Centrophorus cf. uyato, from the Cayman Trench, W.I.

Age determination is an effort to define one of several life-history parameters required to estimate the population dynamics of Centrophorus cf. uyato. Deep-sea commercial fisheries have been established in areas of the world where other Centrophorus populations are located. Understanding the population dynamics of this species will provide some of the data required to help prevent over exploitation should a deep-sea commercial fishery establish in this area. Over the two-year period between August 2000 and March 2002, 54 specimens were captured (7 males and 47 females) from depths of 250-913 m. Age was determined from cross-sectioned dorsal fin spines. Growth curves were constructed and size and age at maturity determined for all readable samples.

A new species of nurse shark from the Pacific Ocean

A new species of nurse shark from the Pacific Ocean is described. It differs from the Atlantic nurse shark, Ginglymostoma cirratum, in body proportions, anatomical characteristics, tooth morphology, and dental formula. The name of the new species will be announced at the meeting.

Reproductive biology of silky shark Carcharhinus falciformis off the west coast of Baja California Sur

The silky shark inhabits warm-tropical and subtropical waters throughout the world. In the eastern Pacific it ranges from Baja California Sur to Peru. Even though it is heavily exploited in the Gulf of Mexico and in the Pacific coast, its reproductive processes have received little attention. The species appears in the waters off the Pacific coast of Baja California Sur from June to October. Generally, adults are more common in the captures. The overall sex ratio was 1:0.6 females per male (n = 295). Clasper development and the presence of sperm aggregates suggest that males mature at about 182 cm TL, while ovarian egg diameters and the presence of uterine eggs or developing embryos show that female maturation occurs at about 180 cm TL. The reproductive anatomy and the sperm storage of.both male and female are described. Gestation appears to last about twelve months. We noted the absence of a defined seasonality for reproduction in the west coast off Baja California Sur populations.

Fishery, uses and conservation of freshwater stingrays (Chondrichthyes: Potamotrygonidae) in the Marajó Bay (Brazil)

Freshwater stingrays present unique but poorly known biological characteristics and belong to the only group of elasmobranchs completely restricted to freshwater habitats. The Marajó Bay is located in the mouth of the Amazon River and the present study observed aspects related to the fishery and uses of potamotrygonids in this region. Direct field observations, analysis of captures / landings and interviews with local habitants were carried out since 1999. Results indicated that there are 2 types of fisheries and several folklore uses attributed to freshwater stingrays. The captures take place in fishing areas that are predominantly located in islands and involve mainly the use of hook and line, nets and long lines. One of the fisheries is directed to newborn and juvenile specimens that are captured for ornamental purposes and at least 4 species are illegally being explored. These captures are very specific since the rays have to be kept alive / healthy and also depend directly on the market demand. The second type of fishery is practiced by artisanal fishermen and involves the capture of adult specimens as a food source. In this case, occasionally the freshwater stingrays are considered bycatch but in some localities there is a directed fishery. The use of potamotrygonids as edible fish is apparently uncommon in other parts of the Brazilian Amazon basin. Freshwater stingrays are locally also used for unusual / bizarre purposes that range from the preparation of folklore medicine to the use of stings in religious rituals. A quota system should be established in the State of Pará in order to try to.regulate the fishery for the ornamental trade and the artisanal fishery for consumption should be kept at sustainable levels. Fisheries and other uses of potamotrygonid species require the observation of specific consevation recommendations and adequate management.

Some aspects of fisheries biology of the silky shark, Carcharhinus falciformis, in Taiwanese waters

A total of 469 specimens (213 females and 256 males) collected from August 2000 to January 2002 at Nanfanao fish market, northeastern Taiwan was used to examine the age ad growth, reproduction, and feeding biology of the silky shark, Carcharhinus falciformis, in the waters off Taiwan. The age and growth was determined by annulus counts of caudal vertebra and 11 and 105 14 annuli were counted for females and males, respectively. The monthly changes of marginal increment indicated that translucent and opaque zones on vertebral centra were formed once per year between November and January. The parameters of von Bertalanffy growth equation (VBGE) were estimated as follows: Linf =358cm TL, K=0.072/yr, to =-3.05 for females; Linf =326cm TL, K=0.091/yr, to =-2.48 for males. The length at birth was estimated to be 63-75cm TL. Sex ratio of embryos was estimated to be 1:1. Females and males mature at 201-220cm and 208cm TL, which correspond to 8.2-10.2 yrs and 8.7 yrs, respectively. Stomach content is comparatively low and scombers and cephalopods were the dominant food items for this species.

Habitat use of the manta ray (Manta birostris) in Hawaii

The manta ray (Manta birostris) is coming under increasing pressure from fisheries, yet very little is known about their basic ecology. Manta rays were acoustically tracked along the leeward coast of the island of Hawaii to investigate their fine scale habitat use. Results of this on-going study will be discussed, along with possible relationships to the feeding ecology of the manta.

Estimates of sharks represented in the global shark fin trade and assessment of sustainability

The burgeoning and largely unregulated trade in shark fins is believed to represent one of the most serious threats to shark populations worldwide. Given the deficiencies in global shark fin production and trade statistics, quantitative studies of the world’s major market for fins in Hong Kong were undertaken to better understand the quantity and species composition of sharks represented. Approximately 29% of daily merchant association auction records were obtained for an 18-month period spanning October 1999 to March 2001. Chinese trade names for fins contained on the sheets were mapped to taxonomic nomenclature using molecular genetic techniques. Bayesian statistical modelling and data-filling methods were implemented in WinBUGS to address the missing records and derive estimates of the total traded weight of fins for each shark species. The model was then expanded to convert fin weights into estimates of the number and landed weight of shark species represented by the trade. These estimates for the Hong Kong auctions were then extrapolated to the entire global trade, using figures from national customs databases. Comparison of landed weight estimates from the trade to the total shark capture production reported to the Food and Agriculture Organization (FAO), allows inferences regarding the accuracy of FAO figures and the degree of utilization of captured sharks in the fin trade. A simple evaluation of the sustainability of existing fin trade demands on shark populations will be presented based on a Schaefer model for blue sharks (Prionace glauca).

Growth in captive smalltooth sawfish, Pristis pectinata

All species of sawfish are listed as endangered to critically endangered on a global basis. The smalltooth sawfish, Pristis pectinata, is listed as critically endangered in the western Atlantic, and has been extirpated from much of its former range. Many details on the life history of this species are lacking in the literature. Although limited in scope, information from captive specimens may provide information on growth that is otherwise unavailable. We provide results on growth from nine captive specimens, four males and five females. These results indicate that smalltooth sawfish are indeed slow -growing and long-lived. Because of limitations in sample size and size range included, these results are only preliminary in nature. Missing are the critical upper and lower size ranges for this species. Data were fitted to the von Bertalanffy growth model, resulting in the following parameters: k = 0.067 yr-1 , t0 =-2.57 yrs., Linf = 385.4 cm , and k = 0.034 yr-1 , t0 = -4.09 yrs. , Linf = 469.9 cm, for males and females respectively. Although the parameters predict a realistic size at birth of 60 cm TL, limitations of the dataset lead to an underestimate of Linf , as smalltooth sawfish attain a maximum length of 600cm, and have been reported to reach 760 cm TL. Additional institutional collaboration may add valuable data particularly for the small juveniles. These results provide insight into the shape of the growth curve despite the limitations imposed by captivity, sample size, and size range included. Additional information on morphometrics allowed us to estimate the weight length relation, W(kg) = 4.0 x 10-5 TL(cm)2.565 , and the TL to FL relationship, FL = 0.91 TL + 9.62.

Case studies of elasmobranch husbandry at Oceanário de Lisboa II

During 2002 Oceanário de Lisboa introduced two large Mobula mobular, one large Manta birostris and two small Prionace glauca in its Opean Ocean 5.000 m3 exhibit. Notes on the husbandry challenges created by the introduction of such unusual species are given, with regards to feeding and general behavior.

Investigating the population dynamics of elasmobranchs: past, present, and future

Population dynamics attempt to describe changes in the cohort-specific abundance of a population in space and time as a result of ecological and genetic processes. Three basic vital rates (birth, growth, and death) and the demographic processes of emigration and immigration, under the effect of various sources of stochasticity, ultimately determine population abundance and fate. Thus, an ideal population dynamics model should capture the interaction of vital rates and demographic processes with all sources of variability. However, the reality for elasmobranch population modeling is quite different. Our knowledge of basic vital rates and demographic processes is still fragmentary for most species, let alone our grasp on the spatial distribution of populations, stock-recruitment dynamics and the effect of most sources of 13 stochasticity on elasmobranch populations. However, considerable progress has been made in the last decade alone. The population modeling approaches applied to elasmobranchs are reviewed and models classified according to their structure (biomass or cohort based), type, cohort type considered, and treatment of time and uncertainty. One main conclusion that emerges is that there may be greater predictive return from investing in increased data collection and quality rather than model sophistication.

Phylogenetic relationships of stingrays: insights from the Eocene Green River genera

The results of a phylogenetic analysis of stingray genera, based on morphological characters, will be presented. The analyses were undertaken as part of a larger study describing a new fossil freshwater stingray genus from the Green River Formation of Wyoming (Early Eocene). The impact of the new taxon (and that of Heliobatis, the other stingray genus from Green River) on the phylogenetic relationships of Recent stingrays will be discussed. The results of our phylogenetic study of stingrays, the most comprehensive to date based on morphological characters, contradicts those of previous authors in relation to various components. Biogeographic implications concerning the evolution of the Neotropical freshwater stingrays (Potamotrygonidae) will be advanced, suggesting that potamotrygonids are considerably older than previous (Late Miocene) estimates.

The Odontobase project: first results

The Odontobase project has been created two years ago to permit an identification of chondrichtyans fishes by the mean of their isolated demo-epidermic structures (dermal denticles, thorns, tubercles, bucklers). This identification is based on the study of all species of sharks, skates and chimaeras at different stages of growth and is focused on the morphology of the basal plate, peduncle, crown, on the relations between peduncle and crown and on the presence of superficial relief. Twenty morphological characters have been identified and used in a first attempt in European species. The first results indicate that the characteristics of the isolated dermal structures can be used sometimes to the specific level in some genera (Somniosus, Alopias) and only at the generic level for other ones (Scyliorhinus, Rajidae). These first observations confirm that some genetically and ecologically closely related groups share the same type of dermal covering and permit to question on the validity of some species.

Age, growth and maturation of the finetooth shark, Carcharhinus isodon, in southeastern U.S. waters: a preliminary report

The life history of finetooth sharks, Carcharhinus isodon, in the coastal waters off South Carolina was studied by determining age, growth and size at maturity. Finetooth sharks were collected from the near shore and estuarine waters of South Carolina from April 2002 through April 2003. Cervical vertebrae were extracted from 111 finetooth sharks (49 males and 62 females), ranging in size from 380 to 1262mm FL, and were prepared for age analysis using standard techniques. The annual periodicity of growth band formation was partially verified using marginal increment analysis. Sex specific von Bertalanffy growth models were generated using observed and back calculated data. To determine size and age at which 50% of the population is mature a logistic model was fitted to binomial maturity data using least squares non-linear regression. Females were considered mature if gravid or contained eggs larger than 26 mm in diameter, or when the oviducal gland was 20 mm or greater. Calcification of claspers, ability of claspers to rotate anteriorly, ability of siphon sac to inflate, and the ability of rhipidion to open freely were noted to assess maturity in males. There is a growing body of evidence which indicates that regional differences in important life history characteristics exist within shark species. As a result, the future direction of this study is to compare the life histories of finetooth sharks in the western North Atlantic and the Gulf of Mexico.

Reproductive biology and habitat utilization of skates along the eastern Bering Sea continental slope.

The reproductive biology and habitat utilization of skates collected along the eastern Bering Sea continental slope was studied (EBSCS). Data were collected during a National Marine Fisheries Service (NMFS) exploratory research cruise along the EBSCS during June-July 2002. A total of 1,330 specimens comprised of nine species were examined for reproductive information. The survey area extended the length of the EBSCS from northwest of Unalaska Island (55° 95’N, 168° 51 92’W) to the southern Navrin Canyon (60° 16’N, 179° 68’W) in waters ranging from 209 to 1,556 m deep. The survey area was divided into two strata types, one by area and another by depth. The EBSCS can be characterized by three distinct habitats; a broad, gentle, sloping area referred to as shelf habitat, areas bisected by submarine canyons referred to as canyon haitat, and areas of steep profile referred to as slope habitat. Skates are an important component of the demersal fish community along the EBSCS and are commonly caught in groundfish fisheries. Despite the abundance and diversity of skates in this region very little is known about their basic life history and ecology. The results presented are part of an ongoing, broad-based, study of the demersal chondrichthyan fauna in the eastern North Pacific and Bering Sea.

Collapse of shark fishery in the Gulf of California, Mexico

During 1995 to 2002 we visited two fishing camps in the Gulf of California, Mexico: San Francisquito and El Barril, B.C., there, elasmobranch fishery is artissanal; fishermen use 22ft vessels, drift-gillnets (10-12in sms) for big sharks, and bottom-gillnets (6in sms) for small sharks, skates and rays. We observed elasmobranch catch composition. Shark’s CPUE was calculated based on landing registries of June and July 1991, 1994 and 2002. We also did a census in a carcasses’ waste ground to compare with catch composition. Main organisms catched with driftgillnets were individuals of families: Charcharhinidae, Sphyrnidae and Alopiidae. Rhinobatos productus and Mustelus californicus were the main species catched with bottom-gillnets. Although the Gulf of California is an important shark congregation area to mate and as nursery, due to overfishing, results show a decreasing tendency of CPUE, reaching a collapse in July 2002, when companies had to stop fishing in the middle of the season.

The diet of the sandbar shark, Carcharhinus plumbeus, in Chesapeake Bay and adjacent waters

Chesapeake Bay, USA and the barrier islands of Virginia’s Eastern Shore are important nursery grounds for the northwest Atlantic population of the sandbar shark Carcharhinus plumbeus (Carcharhinidae). The abundance of species in the Bay during the summer months (May through October) provides a diversity of prey items for both neonates and returning juveniles. The sandbar shark’s role as a predator in the summer food web of Virginia coastal waters indirectly affects commercially important species, and monitoring its diet is an important component of ecosystem-based management. Previous studies of sandbar shark diet have encompassed very small study areas (Chincoteague Bay, VA, USA) and very large areas (from Georges Bank to Cape Hatteras). This study has characterized the diet of C. plumbeus in the Chesapeake Bay, Virginia, as well as the adjacent waters Virginia’s Eastern Shore, highlighting differences in diet within various portions of the nursery area, as well as ontogenetic changes in diet. Stomach samples were obtained in 2001 and 2002 from 234 sharks caught in gillnets or by longline gear. These data were analyzed using standard diet indices of frequency of occurrence, number, and weight for each prey type. Historical data from the Virginia Institute of Marine Science (VIMS) Shark Ecology program were also analyzed. Ontogenetic changes in diet were evident, with crustacean prey decreasing in importance and frequency with increasing shark size, and elasmobranch prey importance and frequency increasing with increasing shark size. While previous research in Chincoteague Bay, VA showed the blue crab, Callinectes sapidus, as the dominant crustacean in sandbar shark diet, the mantis shrimp, Squilla empusa, dominated the crustacean portion of the diet in this study.

Trophic spectrum of Pacific angel shark Squatina californica in the southern Gulf of California, Mexico

During September 2000 to May 2002, shark stomach contents were sampled monthly in the southern Gulf of California, Mexico. The objective to our study is to know the spectrum trophic of Pacific angel shark, Squatina californica, and their variations by lenghts and sex. We apply the Index of Relative Importance as a measure of trophic preferences. A total of 376 stomachs were examined, which 163 (43%) contained food and 213 (57%) were empty. The spectrum trophic was of 22 prey species, 14 fishes, 2 cephalopods and 5 crustaceans, corresponding to 12 family, 11 genus, and 14 species. According to the Index of Relative Importance, the most importance prey were the fishes (67%) and unidentified organic matter (11%), followed by benthic fishes, mainly Daisy Midshipman Porichthys margaritatus (6.2%), Diplectrum spp (4.1%) and the inotted lizardfishes Synodus evermanni (3.6%). The analysis of importance of each sex, indicated that females feed more on fishes and unidentifies organic matter, representing 62.4% and 10.5% respectively. The fish P. margaritatus (10.9%), Diplectrum spp (6.8%), S. evermanni (1.8%) and rainbow cusk eel Ophidion iris (1.6%); while males, the rest of fishes contributed 71.4% of the food supply, the unidentified organic matter represented 88.3%, the peanut rock shrimp Sicyonia penicillata (8.5%), Diplectrum spp (5%) and lizardfish S. evermanni (3.3%). No significant differences were found in the gravimetrical composition of prey species between sexs (P > 0.05).

Pristiform molecular phylogeny

The sawfishes, family Pristidae, is comprised of seven species: Anoxypristis cuspidata, Pristis clavata, P. pectinata, P. perotteti, P. pristis, P. microdon and P. zijsron. Uncertainty remains about systematic relationships for several of these species (e.g., the P. perotteti/microdon/pristis complex). In an effort to elucidate the evolutionary pattern of inter-relatedness for the sawfish group, we sequenced three mitochondrial genes (NADH-2, NADH-4, and Cytochrome B), and one nuclear gene, rag1 for representatives of six sawfish species. A hypothesis of pristiform evolution is discussed in the context of molecular inference, morphology-based hypotheses, and geographical distribution of the group.

Breeding biology of the lemon shark, Negaprion brevirostris: inference through genotypic reconstruction of unsampled adults

We present a new technique involving computer-assisted, manual genotypic reconstruction of unsampled individuals to infer parentage and patterns of breeding in the lemon shark, Negaprion brevirostris. By employing nine highly variable microsatellite loci, we used genetic tags of unsampled parents to demonstrate that lemon shark mating is polyandrous, iteroparous 63 and that the same females return biennially to a particular nursery to produce litters of 8 to 18 half-siblings. In contrast, males rarely if ever return to the same nursery. Between 1995 and 2000 we sampled 910 lemon sharks. We determined year-of-birth for 735 young sharks and assigned these young to sibling groups using the program Kinship. We then used the sibling groups to reconstruct genotypes for their unknown parents. We were thus able to assign 710 juvenile sharks to one of 45 female genotypes (96.3%) while 485 (66.0%) were assigned to one of 84 male genotypes. Results demonstrated that adult females reliably and accurately returned to Bimini, Bahamas on a biennial cycle for parturition, and the majority of litters were the result of polyandry (multiple mating with two or more males) by females. However, adult males rarely sired more than one litter at Bimini. Thus, males almost certainly mate over a broader range than females and our finding of low genetic diversity throughout the western Atlantic is likely explained by male-mediated gene flow. Genetic tagging of unsampled adults, based on multilocus genotypes of newborn sharks, proved to be an effective method of unraveling details of the breeding biology of this protected large, coastal, species.

Conservation of smalltooth sawfish (Pristis pectinata) in U.S. waters

Sawfish are among the most endangered fish in the world and yet even the most developed countries have failed to make sawfish conservation a priority. As with other elasmobranchs, the low reproductive potential of sawfish leaves them exceptionally vulnerable to overexploitation and slow to recover from depletion. Scientists with keen awareness of these characteristics stand to influence and improve management of this and other elasmobranch species, yet this potential remains largely untapped. The United States has a stated commitment to precautionary shark management and has led international elasmobranch conservation efforts, including a 1997 proposal to restrict international trade in all sawfish species under the Convention on International Trade in Endangered Species (CITES). Domestic sawfish recovery, however, has not been a U.S. priority due in large part to lack of active, public pressure. The U.S. population of smalltooth sawfish (Pristis pectinata) is estimated to have declined by more than 95% and to require more than a century to rebuild. There are no federal sawfish regulations; existing Atlantic and Gulf state measures are inadequate to protect the population. The National Marine Fisheries Service (NMFS) has yet to take final action on a 1999 petition from The Ocean Conservancy to list smalltooth sawfish as Endangered under the U.S. Endangered Species Act, although the final decision is expected soon. This process involved a comprehensive scientific status review for the species and a resulting NMFS proposal for ESA listing that, if finalized, would prompt a recovery plan and may result in designation of sawfish critical habitat and protection of look alike species (Pristis perotteti). The history, latest developments and next steps related to U.S. sawfish recovery efforts will be reviewed with a view toward encouraging increased participation from scientists in the management process for this and other imperiled elasmobranch species.

Stomach contents of pelagic sharks in the Eastern Pacific Ocean

The bycatch of large predators, including sharks is common in the tuna purse-seiner fishing in the Eastern Pacific Ocean. We analyze 508 stomach contents from 6 shark species and three shark groups, which were sampled at sea by observers of the Inter-American Tropical Tuna Commission (IATTC) aboard of vessels from Colombia, Mexico, Panama, and Venezuela. The purse-seine sets yielding the samples were distributed across the geographical range of the EPO tuna fishery during December 1992 through September 1994. Our results including that Blue shark (Prionace glauca) predate mainly on cephalopods (decapods), Argonauta spp. and Onychoteuthis banksii. The Bull shark (Carcharhinus leucas) feed on Auxis spp. and cephalopods. Silky shark (C. falciformis) predates on Engraulis mordax, Cubiceps pauciradiatus and Decapterus spp. The mako shark (Isurus oxyrinchus) consumes Abraliopsis spp., Acanthocybium solandrii, Auxis spp. and Euthynnus lineatus. The white nose (Nasolamia velox) feed on Katsuwonus pelamis and Thunnus albacares; whereas the oceanic white tip (C. longimanus) predate on C. pauciradiatus and Stenoteuthis oualaniensis. The group of hammerhead sharks feed on cephalopods (S. oualaniensis, Dosidicus gigas, and Abraliopsis falco. The.group of thresher sharks consumes on epipelagic fishes as E. mordax, C. pauciradiatus and mesopelagic fishes as Benthosema panamense. The carcharhinid group feed mainly on E. mordax. Discussion on width breadth and overlapping between shark species will be shown.

Organochlorine contaminants in sharks of the U.S. east coast

Even at sub-lethal concentrations of exposure, organochlorine contaminants such as pesticides and industrial chemicals pose significant health hazards to marine organisms. These compounds have been associated with a variety of health disorders in several taxa, especially those inhabiting increasingly degraded nearshore and estuarine habitats. Due to use of such regions as pupping and/or nursery grounds, certain shark species are often exposed to organochlorine contaminants at concentrations that may have detrimental effects on embryonic development, maturation, growth, and/or reproductive activity. However, despite the risks that such effects pose to these fishes, few studies have investigated the levels of these compounds in elasmobranch populations. To address such concerns, the present study describes organochlorine levels in three shark species (the bonnethead shark Sphyrna tiburo, blacktip shark Carcharhinus limbatus, and the sandbar shark Carcharhinus plumbeus) inhabiting estuaries and nearshore regions of the east coast of the United States. Topics including routes of exposure and potential effects of contaminant accumulation are discussed.

Habitat use by three shark species in Charlotte Harbor, Florida

A series of 19 acoustic hydrophones were placed in lower Pine Island Sound, Charlotte Harbor, Florida, to monitor the movement patterns of three shark species. A total of 58 blacktip (Carcharhinus limbatus), bonnethead (Sphyrna tiburo) and bull (Carcharhinus leucas) sharks were collected within the study site and fitted with acoustic transmitters for long-term monitoring efforts. Twenty-six young-of-the-year blacktip sharks were monitored for periods of 1-157 days. Twenty-one bonnethead sharks varying in size and age were monitored for periods of 1-104 days. Eleven bull sharks (125-183 cm TL) were monitored for periods of 3-52 days. Examination of movement patterns of the three species was used to define any overlap or differences in habitat use. Blacktip and bonnethead sharks appeared to use smaller activity spaces and be more resident within the study region than bull sharks. Bull sharks moved into and out of the study region regularly and overlapped their habitat use with those areas used by blacktip and bonnethead sharks. Movement and behavior patterns observed for all three species will be discussed.

Investigations of a primary nursery area for the blacktip shark, Carcharhinus limbatus, in Quintana Roo, Mexico

The blacktip shark is one of the most important and heavily exploited elasmobranch species in the Mexican artisanal fishery of the Gulf of Mexico. A collaborative team of researchers from Mexico and the U.S. have undertaken a long-term tagging study of young blacktips in Laguna Yalahau, a semi-enclosed lagoon in the northeastern Yucatan peninsula. The project’s biologists worked closely with local gillnet fishermen during the peak pupping season to find and capture the sharks for tagging. Since 1995, a total of 390 gillnet sets were made during 6 expeditions to the lagoon resulting in the tagging of 1,160 neonate and young-of-the-year blacktip sharks. Additionally, Peterson mark-recapture methodology was employed during the last two tagging expeditions which estimated that approximately 1,000 sharks were inhabiting the lagoon during our sampling. Of these tagged and released sharks, a total of 205 recaptures have been subsequently reported (17.7%) to us to date. If this high recapture rate is indicative of the fishing pressure on these first-year sharks, it raises interesting questions about the sustainability of fisheries targeting very young animals. These results will be discussed in light of the unique socio-economics and history of this Mexican lagoon.

Distribution of deep-water elasmobranchs and correlations with hydrographic variables in the U.S. Gulf of Mexico

The impact of both target and non-target fisheries mortality on elasmobranch stocks is of increasing concern world-wide. Most elasmobranch fisheries have proven unsustainable as evidenced by the collapse of directed shark fisheries. Increasing exploitation of deep-water elasmobranchs combined with a general lack of knowledge of their ecology, establishes the need for investigations into life history, ecology, and fishery response. Bottom trawl surveys that are useful for assessing U.S. Gulf of Mexico (Gulf) elasmobranchs were conducted from 1988 to 1996 by the National Oceanic and Atmospheric Administration (NOAA)/National Marine Fisheries Service (NMFS). All finfish and elasmobranchs were weighed, enumerated, measured for length and, in many cases, sexed. Bottom trawling at 911 stations was conducted for 30 minutes with either a 27.5 m high-opening bottom trawl.(HOBT) or a 37.5 m Shuman trawl in depths from 12 m to 406 m. Environmental data (i.e., station depth; surface, midwater and bottom temperature; surface, midwater and bottom salinity; and midwater and bottom dissolved oxygen) were also collected. Elasmobranch distributions were both visually and statistically analyzed. Multivariate analysis of variance (Wilks’ l=0.113, P < 0.0001) and canonical linear discriminate function analysis [eight out of nine canonical variables found to be significant (P < 0.01 for each)] indicated environmental differences between elasmobranch species, with station depth, dissolved oxygen and salinity the primary factors affecting distribution. Visual analysis of distribution maps indicated Gulf-wide occurrences for many species. The five most frequently occurring species [genus species, frequency of occurrence (i.e., number of occurrences/number of trawls)] were Atlantic sharpnose shark (Rhizoprionodon terraenovae, 0.216), Atlantic angel shark (Squatina dumeril, 0.108), smooth dogfish (Mustleus canis, 0.086), Cuban dogfish (Squalus cubensis, 0.043), and spreadfin skate (Raja olseni, 0.029). Using such a multi-species/ multivariate environmental approach augments a major goal of NOAA’s strategic plan to protect, restore, and manage use of coastal and ocean resources through ecosystem management.

The sexually dimorphic cephalofoil of bonnethead sharks

We have documented an overlooked sexual dimorphism in the head shape of a common, wellstudied species of shark, the bonnethead Sphyrna tiburo. Sexually mature male bonnethead sharks have a distinct bulge along the medial, anterior edge of the cephalofoil. This change in morphology is attributed to the elongation of the three rostral cartilages in the snout of the males at the onset of sexual maturity. A Procrustes analysis revealed that the head shape of adult males differs significantly from adult females and immature males whereas the head shape of embryonic and juvenile sharks does not differ between the sexes. The elongation of the rostral cartilages corresponds temporally with.the elongation of the clasper cartilages in males. We suppose that the same mechanism responsible for stimulating growth of the clasper cartilages secondarily affects the rostral cartilages. If true, the phenomenon of rostral cartilage sexual dimorphism in elasmobranchs may be more widespread than previously imagined. Such a widespread dimorphism would be difficult to detect by eye because of the already pointedsnout morphology of most shark species. Our results also have taxonomic implications for the genus Sphyrna. Head shape of Sphyrna tiburo tiburo, the bonnethead from the Atlantic was compared to Sphyrna tiburo vespertina, the Pacific bonnethead shark. A significant difference was again found between the subspecies, with the Pacific specimens of both sexes having a head 32 morphology that more closely resembled mature males from the Atlantic. The Procrustes analysis points out a significant morphological difference that was not apparent to the investigators who synonymized S. vespertina into Sphyrna tiburo, and perhaps it should be restored to specific status.

Phylogeography of the blacktip shark, Carcharhinus limbatus, based upon mitochondrial control region sequences

While many coastal shark species have discontinuous distributions along tropical and subtropical continental margins, very little is understood about the origins, historical dispersal, and current levels of conductivity of their widespread populations. We analyzed geographic patterns of variation in the mitochondrial control region from blacktip sharks, Carcharhinus limbatus, to investigate genetic relationships among disjunct, extant populations of this species. Phylogenetic analysis of blacktip sharks collected from the coasts of South Africa, western Australia, eastern Australia, Baja California, the Caribbean Sea, the Gulf of Mexico, and the western North Atlantic Ocean produced two distinct groups of haplotypes separated by 8 substitutions: an Atlantic Ocean/Gulf of Mexico/Caribbean Sea group and an Indian Ocean/Pacific Ocean group including Baja California. A much lower amount of variation was observed within these two groups and haplotypes differed by few substitutions versus comparisons between groups. Issues such as centers of radiation, historical dispersal patterns, and current gene flow will be addressed.

Comparative morphology of dermal denticles of Rhizoprionodon (Elasmobranchii, Carcharhinidae) and related genera

The morphology of dermal denticles in six species of Rhizoprionodon (R. lalandii, R. porosus, R. terraenovae, R. oligolinx, R. acutus and R. taylori), Loxodon macrorhinus and Scoliodon laticaudus were comparatively investigated by optical and Scanning Electron Microscopy. Ontogenetic variation was estimated on the basis of growth series of R. lalandii. Dermal denticles of mouth floor, nictitating eyelid, anal fin, clasper and lateral trunk were examined in search of phylogenetically informative characters. Comparisons of skin samples of the same individual revealed that there is no significant differences in the morphology of dermal denticles in various portions of the trunk (i. e., lateral, dorsal and ventral portions). Species comparisons resulted in differences in number of cusps, keels, ornamentation and relative proportion of each scale (height x width). Trunk dermal denticles of species that reach larger body size when adults, generally have more numerous keels and cusps. In Rhizoprionodon, dermal denticles become more complex in form and distribution with increasing growth. In juveniles, dermal denticles are more sparsely distributed, with fewer keels and cusps than adults. Pre-adults have a combination of juvenile and adult denticles, alternating simpler regions with more complex ones.

Phylogenetic inference of the order Squaliformes based on nuclear and mitochondrial sequence data

The superorder Squalomorphii includes the Hexanchiformes, Pristiophoriformes and the Squaliformes. The Squaliformes are grouped into 6 families, 22 genera and roughly 87 species; however, there are several taxonomic uncertainties regarding this group. Representatives for 13 out of the 22 known Squaliform genera were sequenced for the mitochondrial genes NADH-2, NADH-4, Cytochrome B, and the nuclear gene rag1. These sequences were used in phylogenetic analysis. Hypotheses for inter-generic relationships supported by our data will be discussed and compared with previous morphological and molecular hypotheses.

Observations on the skeleton of the heterocercal tail of sharks (Chondrichthyes: Elasmobranchii)

We present new illustrations and descriptions of the skeleton of the heterocercal tail of twelve species of sharks represented by multiple adult specimens. Nine species from the family Carcharhinidae were examined (bull shark, Carcharhinus leucas; blacktip shark, C. limbatus; dusky shark, C. obscurus; sandbar shark, C. plumbeus; tiger shark, Galeocerdo cuvieri; Atlantic sharpnose shark, Rhizoprionodon terraenovae; bonnethead, Sphyrna tiburo; great hammerhead, S. mokarran; and scalloped hammerhead, S. lewini). We also studied one species of Alopiidae (common thresher shark, Alopias vulpinus), as well as one species of Ginglymostomatidae (nurse shark, Ginglymostoma cirratum) and one species of Triakidae (smooth dogfish, Mustelus canis). Our most interesting observations concern anatomical relationships of the hemal arches and hypural elements that support the ventral fin-web of the hypochordal lobe of the caudal fin and the modified neural arches and spines that support the epichordal portion of the caudal fin. The patterns of these skeletal elements differ in many details from the patterns described previously for the heterocercal caudal fin of actinopterygians such as paddlefishes, and these differences offer insight into general aspects of the anatomy of heterocercal caudal fins. This paper is in honor of Hans-Peter Schultze and his many contributions to the anatomy and systematics of vertebrates. Supported by DEB-0075460 and the Jane H. Bemis Fund for Research in Natural History.

Caudal spine replacement rates of the round stingray (Urolophus halleri): implications for public safety

The round stingray (Urolophus halleri) is a common ray along nearshore sandy beaches and bays in southern California. This ray is particularly abundant along Seal Beach, California during summer and fall months where 200-400 stingray-related injuries are reported annually. In an attempt to reduce injury to beach goers, a stingray spine-clipping study was conducted. To evaluate the efficacy of spine-clipping, natural spine replacement rates and population size of stingrays at Seal Beach was determined. Of the 2183 stingrays caught, tagged, and released at Seal Beach, only 13 (0.06 %) have been recaptured over a 3-year period, indicating a large, mobile population. Spine lengths of all rays caught were measured to determine spine shedding rates for the population. Field and laboratory studies indicate spines are not replaced as a direct result of removal or clipping. Spine replacement was observed between August through October, when a majority of rays were found with two spines, one primary (1°) and one secondary (2°). The 2° spine is first detectable under the 1° spine in July, and by August the 2° spine is 50-75% the length of the 1° spine. Laboratory studies confirm annual spine replacement and shedding of the 1° spine. The large population size of Seal Beach stingrays and timing of spine replacement indicate that even a large-scale spine-clipping program would be ineffective in reducing risk to beach goers.

Movement patterns of tiger and Galapagos sharks around French Frigate Shoals, Hawaii

During the summer months, breeding activity results in an increased abundance of sea birds, sea turtles and Hawaiian monk seals in the Northwestern Hawaiian Islands. This may represent an increased source of prey for sharks. To correlate shark activity with seasonally increased prey density around French Frigate Shoals (FFS), Hawaii, acoustic listening stations were placed around six small islands throughout the atoll. Thirteen tiger sharks (Galeocerdo cuvier) and four Galapagos sharks (Carcharhinus galapagensis) were surgically fitted with long-life acoustic monitoring transmitters. Tiger sharks were detected at all islands throughout the atoll and exhibited a strong affinity for East Island (in the center of the atoll) during June and July. Peak detection frequency occurred between 05:30 and 10:00. This activity coincided with the early summer fledging period of blackfooted and Laysan albatross on East Island. Tiger sharks were first detected around the island approximately 1 month prior to fledging and their activity markedly decreased within days after the end of fledging. In winter months, tiger sharks were usually detected near islands in the northern part of the atoll, where peak detection frequency occurred between 21:00 and 03:00. Galapagos sharks were only detected at islands in the north edge of the atoll (particularly Trig Island), during summer and fall when a.majority of the monk 69 seal pups are born. These islands provide seasonal increases in semi-terrestrial prey availability that appears to influence the behavior of these large sharks.

Feeding kinematics of the leopard shark Triakis semifasciata Girard 1854: an ontogenetic perspective

Though limited, research regarding ontogenetic changes in the feeding kinematics and behavior of elasmobranchs suggests that substantial changes may occur during neonatal stages. These changes are hypothesized to correlate with predator abilities, prey attributes, and/or changes in fluid dynamics. To establish whether ontogenetic changes in feeding kinematics occur in the leopard shark Triakis semifasciata and begin to investigate the basis for these changes, a Redlake high-speed digital video camera filming at 250 fields/s was employed on a weekly basis for one year to record prey capture events in four individuals feeding on five prey types. Several external morphological characters associated with the feeding apparatus of the sharks were also measured on a weekly basis throughout this year. When feeding on dead prey, average bite duration showed a gradual but significant increase (110 – 125 ms) over time, as did the majority of other timing variables. By contrast, timing variables within an individual generally decreased over time when feeding on live prey. Excursion variables tended to decrease in magnitude within an individual over time, with the exception of hyoid depression. The result of this discrepancy is that sharks employed a functionally smaller oral aperture and depressed their hyoid relatively more as they aged. These changes in kinematics were accompanied by negative allometric increases in mouth width and positive allometric changes in mouth length, causing the mouth to become narrowed anteriorly and elongated, presumably facilitating suction feeding. Though suction feeding was used with dead prey over the duration of this study, leopard sharks adopted a ram-dominated feeding modality with respect to live prey as time progressed, indicating a behavioral rather than morphological alteration. The results of this preliminary study indicate that changes in feeding kinematics occur in young leopard sharks and that these changes have both behavioral and morphological bases.

Relative abundance index for pelagic sharks from the lower Gulf of California: exploratory analysis using a D-distribution approach

The lower Gulf of California (GOC) is a key passing area for shark migration toward the interior of the GOC, the west coast of Baja California Peninsula, the Gulf of Tehuantepec, and Revillagigedo Archipelago. Time series from 1986-1999 derived from longline vessels operation were used to estimate cpue (sharks/100-hooks) for Alopias pelagicus, Carcharhinus falciformis and Prionace glauca, using a D-distribution approach. The D-distribution is useful for estimating the mean and variance when catch per set data exhibit a skewed distribution, including zero and large catches, an inherent behavior of marine animal data. The pelagic thresher shark showed two abrupt declines: from 5.12 in 1986 to 2.12 in 1990, followed by an abrupt decline to 1.65 in 1998 after reaching a peak of 6.51 in 1992-93. The cpue trend for silky shark showed a subtle decrease from 2.1 in 1986 to 1.0 in 1996, after stabilizing at about 1.2 from 1992 to 1995. In 1999, both pelagic thresher shark and silky shark showed an increment in cpue to 4.26 and 2.0, respectively. In contrast, the blue shark showed a slight positive tendency with a maximum of 2.6 in 1998. The convenience and limitations of the method applied to fishery data and factors affecting the estimation are discussed.

Shark essential fish habitat

The Magnuson-Stevens Fishery Conservation and Management Act defines essential fish habitat (EFH) as those waters and substrate necessary to fish for spawning, breeding, feeding or growth to maturity. The National Marine Fisheries Service (NMFS) regulatory interpretation of this Act requires that EFH be described and identified within the U.S. Exclusive Economic Zone for all life stages of each species in a fishery management unit. Shark species managed under the NMFS Final Fishery Management Plan for Atlantic Tunas, Swordfish, and Sharks are found in a variety of habitats and have diverse life history characteristics. Many of these shark species are highly migratory and cover a variety of areas and habitats during their seasonal migrations. Habitat preferences for some species also differ during changes from one life history stage to the next. These differences combined with the paucity of life history information available for many species create unique problems in the determination of shark EFH. These problems will be discussed and updated information regarding NMFS shark EFH designations will be presented.

The popular image of sawfishes in Western society and its implications for conservation efforts.

With sawfish populations under serious threat worldwide, there is a critical need to raise general awareness about these charismatic rays. Establishing widespread public concern about sawfishes will be necessary to achieve the monetary and political support needed for pristid conservation initiatives. However, before successful education programs can be developed, it must be understood how sawfishes are currently portrayed in popular culture. To achieve this objective, over 200 depictions of sawfishes were compiled from various media, including cartoons, literature, television, movies, art, and toys. Content analysis was performed on these depictions to identify dominant themes conveyed about sawfishes through the popular media. A second content analysis was then performed to document how sawfishes are depicted anatomically. Overall, analyses of these representations reveal a profound lack of knowledge about actual sawfishes, with highly erroneous notions of pristid anatomy, distribution, and behavior being advanced. While popular and symbolic portrayals of animals should not be expected to mirror zoological reality, an historical unfamiliarity with pristids, coupled with many pervasive misconceptions, has created a dramatic need for basic education about sawfishes in Western society. By educating the public about sawfish life history and dispelling these popular misconceptions, conservationists can generate the awareness, support, and empathy critical for conservation efforts.

Biogeography of fishes of the Gulf of Mexico

A total of 1,454 fish species in 681 genera, and 221 families are documented from the Gulf of Mexico. These totals represent about 64.3% of the species, 79.4% of the genera, and 92.5% of the families recorded from the Central Western Atlantic. A majority of the fishes in the Gulf of Mexico are wide ranging continental fishes, wide ranging insular fishes, and deep-sea benthic and pelagic fishes. Secretive insular fishes are less well represented. Despite the relatively high diversity, only about 5% of the fish species are endemic to the Gulf of Mexico. The majority of the endemic species are limited to either the eastern, northwestern, or southern sub regions of the Gulf. Only 9 endemic species are ubiquitous throughout the Gulf. Based on percent endemicity, the Gulf cannot be considered a cohesive biogeographical region or province. However, based on its high diversity and unique warm temperate and tropical components, the Gulf is a distinct biogeographical area.

Reproductive biology of Centrophorus cf. uyato from the Cayman Trench, Jamaica

Centrophorus is a genus of family Squalidae in order Squaliformes. Members of Centrophorus typically are gray to brown, with large green eyes, spines anterior to both dorsal fins, and pectoral fins that often have a free rear tip that extends well under the first dorsal origin. They are most abundant below 200 meters depth. The organism in this study may be a species of Centrophorus that has not been described previously. Unfortunately, the taxonomy of this genus is currently in a great deal of uncertainty. The characteristics of this species most closely resemble those of Centrophorus uyato, hence our use of Centrophorus cf. uyato. Specimens were obtained via horizontal longline at depths of 250-913 meters. The reproductive biology of 8 male and 51 female cf. uyato have been examined. This species is sexually dimorphic, with females attaining a larger size than males. The smallest mature male was 81.2 cm total length whereas the smallest mature female was 91.5 cm total length. Females are aplacentally viviparous with a maximum of two pups per litter. The pups acquire nutrition via their large external yolk sacs. There was no evidence of additional maternal contributions to the nourishment of the embryos. Oocytes continued to develop throughout gestation. Most females carrying developing embryos had two large (>3.3 cm), equally developed ovarian oocytes, which leads us to believe that they ovulate soon after parturition. This species seems to exhibit complete sexual segregation during the non-breeding season, with mature males being completely absent from the study site during the summer months.

Ontogenetic expression of lymphocyte-specific genes implicate unique lymphoid tissues in generating elasmobranch immune repertoire

The expression of immunoglobulin (Ig), T-cell receptor (TCR), recombination-activating gene-1 (Rag-1), and terminal deoxynucleotidyl transferase (TdT) genes was used to identify the roles of lymphomyeloid tissues during the 12-weeks of embryonic development and after hatching in the clearnose skate, Raja eglanteria. At 8 weeks of embryonic development, Ig and TCR genes are sharply up-regulated. Throughout embryogenesis, TCR and TdT expression is limited to thymus, suggesting this site as a primary source of T-cells as it is in mammals. TCR expression is not detected in peripheral sites (spleen and intestine) until after hatching and in adults, implicating these tissues as potential secondary lymphoid sites. High levels of expression of both Rag-1 and TdT in the thymus are consistent with rearrangement and junctional diversification, respectively, of TCR genes. B-cell expression is more complex. Beginning at 8 weeks of embryogenesis, highest relative abundance of IgM and IgX expression is seen in the spleen while at the same stage, IgX is expressed in greater abundance relative to IgM in Leydig organ, liver, and even thymus. The coincidental embryonic expression of Ig and Rag-1 genes in spleen, liver, Leydig organ and gonad suggests that B-cell development occurs at multiple sites in contrast to the apparent restriction of T-cell development to the thymus. The substantial Ig gene expression in embryonic thymus raises the possibility that thymus could be an additional early site of B-cell development. In adult skates, greatest expression of IgM and IgX is in the Leydig organ.

Comparison of elasticity patterns of elasmobranchs and mammals with review of vital parameters of lamnids

Vital parameters (age-at-first-reproduction, maximum-reproductive-age, age-specific fertilities, and age-specific mortalities) of lamnids were reviewed. Despite progress in the last 20 years, vital parameters of lamnids and many other elasmobranchs are not sufficiently well-known to produce reasonably accurate population growth rates (l). Luckily, the elasticity pattern of a species that is needed to evaluate management proposals is fairly robust and does not require an accurate l. Furthermore, there is no need to calculate l because the elasticity pattern is determined by age-at-first-reproduction (a) and generation time (Abar) alone, with gestation period (GP) providing a refinement: E(fertility) = E1 = 1/Abar; E(juvenile survival) = E2 = (a – GP) E1; E(adult survival) = E3 = 1 – E2 = (Abar – a + GP) E1. These are lower-level elasticities of the vital parameters as they appear in a life history table and E2 includes survival to age one. Therefore, they do not sum to one but are easily normalized. The exclusion of survival to age one from E2 distorts the elasticity pattern, in particular for species with low age-at-first reproduction. Abar is usually not known. However, using an Abar estimate based on the mean Abar/a ratio of 60 elasmobranchs (1.31, coefficient of variation 9.3%, range 1.1-1.8) provided promising results. The elasticity pattern of elasmobranchs as a function of age-at-first reproduction indicated that E2 is largest for all elasmobranchs if a > 1 yr (valid for most if not all elasmobranchs). Accordingly, protection of juveniles will provide the most effective measure to reverse population declines if that has been observed for an elasmobranch species. The mean Abar/a ratio of 50 mammals (2.44, coefficient of variation 33.5%, range 1.2-5.0) is larger and more variable compared to that of elasmobranchs and, accordingly, the elasticity pattern is more complicated.

Historical zoogeography of the Selachii

Analyses were conducted on the zoogeography of the extant orders of sharks, incorporating the most recent phylogenetic and paleontological information. In order to test dispersal and vicariance hypotheses, vagility (dispersal ability) of taxa was estimated by examining the geographic ranges of species and species diversity within each order. Other factors examined were body size, behavioral habit (benthic, benthopelagic, pelagic) and habitat (neritic, bathyal, oceanic). There was a strong negative correlation of size with species diversity. Most sharks are <100cm in total length. Benthopelagic species were slightly more speciose than benthic species and pelagics were depauperate. Surprisingly, although neritic habitat was speciose, species that occupied both neritic (»200m) and bathyal (>200m) or strictly bathyal habitats together contributed the highest shark diversity, whereas oceanic habitats had a small number of species. This contradicts the popular notion that sharks are most diverse in shallow tropical seas. To the contrary, shark diversity is highest in cool or cold deeper water habitats where the order Squaliformes and the Carcharhiniform family Scyliorhinidae are particularly speciose. There was a strong inverse relationship between body size and range. Likewise benthic species had the smallest and pelagic species had the largest ranges. Within the major orders Orectolobiformes, Carcharhiniformes and Squaliformes all showed a strong relationship between body size and range, except for the largest size class (>300cm TL) within the Squaliformes, which is dominated by Somniosus a bi-polar species. The Orectolobiformes, all of which are benthic (except the very large oceanic Rhincodon typus) had smaller ranges at size than either Carcharhiniformes or Squaliformes. Ancient vicariance, the late Jurassic breakup of Pangaea, may be largely responsible for the present distribution of the Heterodontiformes, Orectolobiformes, and Squatiniformes, all benthic, neritic groups with very low vagility. Other groups have high vagility and have dispersed across large expanses of open ocean. Geographic areas of particular interest are Australia with very high shark diversity and endemism and the eastern North Pacific where the diverse bathyal Squaliformes are virtually absent.

Phylogenetic interelationships among the major groups of sharks deduced from molecular sequence data

An estimate of the phylogenetic relationships among different groups of extant sharks will be presented and discussed. The inference is based on sequence derived from 3 mitochondrial genes and one nuclear gene (approx. 5 kb) sequenced for representatives of all recognized extant shark families and the majority of extant genera (approximately 150 taxa).

Bioenergetics modeling of the cownose ray, Rhinoptera bonasus, in the northern Gulf of Mexico

We used two bioenergetics-based models to examine the relationship between somatic growth and reproduction in the cownose ray, Rhinoptera bonasus. Both models simulated the daily dynamics of an individual over its lifetime. One model was a modified version of the classical bioenergetics model, and represents how ingested energy is partitioned among egestion, respiration, excretion, and reproductive products. Prey availability affected ingestion, and all processes were size- and temperature-dependent. The second model, under development, used dynamic optimization to investigate the life history implications of how energy is partitioned between somatic growth and reproduction. Both models assumed mortality rate decreased with cownose ray disc width. Specific laboratory experiments were performed to estimate key parameters of both models. The models were then used to simulate how variation in temperature, prey availability, and reproductive strategies affected the life time growth and pup production of cownose ray in Gulf of Mexico waters. Preliminary results showed that the success of the low-fecundity, low-growth life history strategy of cownose ray is especially susceptible to changes in environmental conditions and mortality rates.

Is angiotensin II a ubiquitous regulator of elasmobranch interrenal gland steroidogenesis?

The presence of the renin-angiotensin system (RAS) has recently been indisputably established in elasmobranchs, but its role in elasmobranch physiology is still unclear. In other vertebrates, angiotensin II (AII) stimulates the synthesis of mineralocorticoids (MC), which subsequently act as antinatriuretic factors. The elasmobranch interrenal gland produces a unique steroid (1a- 32 hydroxycorticosterone; 1a-B) with MC activity, but conflicting evidence exists regarding the AII-dependent regulation of its synthesis. To better define the role of AII in the elasmobranch interrenal gland, we used degenerate primers in coupled reverse transcription/polymerase chain reactions (RT-PCR) to isolate sequence of the AII receptor (AT1 ) mRNA from the euryhaline elasmobranch Dasyatis sabina. These reactions produced a product of the expected size. Subsequent sequence analysis revealed this product to be 70% identical to the eel AT1 receptor mRNA. Specific primers used in RT-PCR indicated the expression of AT1 mRNA in a variety of D. sabina tissues, including the interrenal gland. Quantitative PCR indicated no significant difference in the steady-state expression of AT1 mRNA between interrenal glands of fresh water-adapted and seawater-adapted D. sabina. The sensitivity of the elasmobranch interrenal gland to AII is probably governed by other factors, such as circulating AII concentrations and/or post-translational modification of AT1 . The expression of AT1 in the interrenal gland of D. sabina is an indication that RAS impinges upon the function of the interrenal gland. As 1a-B synthesis is the primary function of the elasmobranch interrenal gland, steroidogenesis is the most likely target of RAS regulation.

Gastric pH changes associated with feeding: using pH to study the foraging ecology of sharks

Little is known about the feeding chronology of elasmobranches due to their high mobility, potentially large size, and difficulties in captive maintenance. Changes in gastric pH of leopard sharks (Triakis semifasciata) were quantified as an indicator of feeding periodicity, frequency and daily ration. Adult leopard sharks were fed automated pH/temperature data loggers and subsequently fed meals of squid for periods ranging from 5-14 d. Ration size was varied 44 between 0.1-2.1 % of the sharks body weight. To determine the effect of the pH probe on acid secretion, gastric samples were taken from juvenile leopard sharks at different time intervals after feeding and pH was measure externally. In situ, continuous measurements of pH shows that empty stomachs have a low pH of 1.54 ± 0.46 (SD) and that feeding causes a rapid increase in pH followed by a more gradual return to baseline levels. There was a strong positive relationship between change in pH and meal size (r2 =0.72, p=0.001). Lab serial.sample measurements show that pH 1 h after a meal was 3.31 ± 0.35, whereas 96 h after a meal pH had dropped to 1.75 ± 0.24. There were no significant differences in pH between continuous in situ, and lab serial sample measurements. Gastric acid secretion may be continuous in leopard sharks and may offer a mechanism to increase digestive efficiency of sharks. Changes in gastric pH can be used to estimate feeding periodicity, frequency and daily ration size in leopard sharks in the wild.

Sharks in peril: a review and analysis of IUCN listed shark species

For a number of reasons, (low fecundity and intrinsic rate of increase, late maturity and long life), many shark species are particularly vulnerable to extinction. As of February 2003, the International Union for Conservation of Nature and Natural Resources (IUCN) has red listed 63 species of sharks worldwide. These species are variously listed as near threatened (31), vulnerable (13), data deficient (9), endangered (5), conservation dependent (4), and critically endangered (1). In this analysis, I review, when available, the life history parameters, distributions, and level of exploitation of the shark species that appear on the IUCN list. Emphasis was placed on those species occurring in the Atlantic. The near threatened (NT) category includes the greatest diversity of species, including many of the largest members of the Carcharhinidae. Other families included in the NT category are the Scyliorhinidae, Lamnidae, and Sphyrnidae. Given the almost complete lack of biological information available for most shark species, it is curious that only 10 species are listed as data deficient (DD). The DD category includes notables such as Sphyrna mokarran and Megachasma pelagios. The families with the greatest numbers of species listed are the Carcharhinidae (20), Triakidae (11), Scyliorhinidae (5), Lamnidae (4), Squatinidae (4), Sphyrnidae (3), Hexanchidae (2), and Odontaspidae (2). Eleven families have a single species listed. It is interesting that the vulnerable category includes the largest sharks such as Rhincodon typus, Cetorhinus maximum, and Carcharodon carcharias. Attention given to these high risk shark species, may suggest additional candidates for listing and can more clearly define necessary conservation measures.

Observations of shark by-catch from the artisanal driftnet fishery in the central coast of Venezuela

The artisanal fishery at Playa Verde, located in the central coast of Venezuela, has the most landings of billfish in the country. Shark by-catch represents, after frigate fish, the third group in importance in these landings. This study describes the species composition, biometry, sexual maturity and CPUE of shark landings from two periods: September 1998 – July 1999 and February – May 2002. Twelve species of sharks, belonging to seven families and four orders, were identified. The most common species landed were, in order of decreasing abundance: Carcharhinus falciformis, Isurus oxyrinchus, Sphyrna lewini, Prionace glauca and Alopias superciliosus. Through a comparative analysis of size structures and sexual maturity stages, adult individuals of A. superciliosus, Carcharhinus obscurus, I. oxyrinchus, Isurus paucus, P. glauca, Pseudocarcharias kamoharai and S. lewini, were observed. However, only pregnant females of A. superciliosus, C. obscurus and S. lewini were recorded. The sex ratio of I. oxyrinchus (3M:1F) and S. lewini (1M:6,7F) deviate significantly from the expected ratio (1M:1F). The largest shark abundance was observed during the first seven months of the year, coinciding with the upwelling period. Yearly CPUE values showed a decreasing trend in 1992-1999, with a slow recovery thereafter. The shark composition reported at Playa Verde, was more similar to those observer by oceanic commercial longliners of tuna and swordfish than from artisanal fisheries from the eastern coast of Venezuela.

Like a rock: structural properties of the shark vertebral column

There is a common perception that the skeleton of cartilaginous fishes must be inferior to that of bony fishes in stiffness and strength. However, this idea has never been tested, and the functional extrema achieved by some sharks casts doubt on this generality. We examined structural properties and composition of the vertebral column of seven cartilaginous fishes. We chose animals that varied widely in morphology, ecological niche, and inferred swimming speed. Strength, stiffness, % water, % mineral, and % collagen were compared among species. Not surprisingly, strength is correlated with the percentage of mineralized tissue. Shark vertebral centra are similar in stiffness to mammalian trabelcular bone (>100 MPa). Average shark centra were 43% water by weight, and dry vertebrae were 47% mineral and 53% dry organic material. The torpedo ray was the only batoid fish in our data set. The ray had lower mineral content and higher water content than the other species and was an order of magnitude less stiff. This trend may be related to the locomotor mode of batoid fishes, as the vertebral column should experience less stress in a pectoral fin undulator than in an axial undulator.

Age and growth of the shortfin mako, Isurus oxyrinchus, from Baja California Sur, Mexico

The shortfin mako shark, Isurus oxyrinchus, is one of the most important species in the commercial and recreational fishery in Mexico. However, little is known about the biology and fishery of this species. The age and growth data is necessary to design an effective fishery management. Age and growth rate of shortfin mako were estimated using the number of growth bands on 93 vertebrae. The sharks were caught on the western coast of Baja California Sur, Mexico, during 2000 and 2003. The technique used for enhancing the contrast of the calcified bands was silver nitrate impregnation. The specimens ranged from 77 to 290 cm Total Length (TL). A significant linear relationship (r2 = 0.92) was found between TL and the vertebrae radius, showing a proportional growth between the structure and body length. The oldest female in the sample was 25 years at 290 cm TL, and the oldest male was 12 years at 208 cm TL. Bands on vertebrae and TL data were used to describe the shortfin mako pattern growth using the von Bertalanffy model. Preliminary estimates of curve parameter with sexes combined were: asymptotic length = 359 cm TL, K = 0.05, t0 = -4.96 years. Results suggests that shortfin mako shark has a slow growth that combined with other life-history traits, such as a low fecundity and a delayed reproduction, makes this species susceptible to overfishing.

Life history parameters of the Dusky Shark, Carcharhinus obscurus, revisited and their implications to estimates of population increase.

Numbers of dusky sharks, Carcharhinus obscurus, in the Western North Atlantic have drastically declined over the past twenty years. Several fishery-dependent and fishery-independent studies have recorded the decline of this slow growing, late maturing, long-lived species. It is imperative for the survival of this species that we develop accurate demographic and biological parameter estimates to ensure proper management. Data sets from the Virginia Institute of Marine Science (VIMS) fishery-independent shark survey, Commercial Shark Fishery Observer Program (CSFOP) fishery-dependent shark survey, and previously published data were analyzed to construct better estimates of gestation period, reproductive periodicity, fecundity, offspring size frequencies, and other biological parameters. These estimates were then used in a stochastic stage-based demographic model to estimate intrinsic rate of population increase and elasticities for population stages.

Variation in morphology and function of batoid wing skeletal elements

The skeleton of the wings of skates and rays consists of a series of radially oriented cartilaginous fin rays fanning out from the pectoral girdle. Each fin ray is segmented into small, longitudinally oriented ceratotrichia, traditionally represented as simple cylindrical building blocks. High-resolution radiography reveals the pattern of calcification in ceratotrichia and their organization within the fin ray to be considerably more complex and variable than previously thought. The length, width and branching pattern of these elements varies between families and within genera. In addition we documented the presence of reinforcing projections running between fin rays. The wings are reinforced in different areas in different families, and among animals with different lifestyles (pelagic, semi-pelagic, and benthic). We interpret this variation as a proxy for differential function and performance. There may be useful characters in this morphology of the ceratotrichia for phylogenetic analysis as there is a great deal more variability than has been appreciated. We suppose that further biomechanical investigation of the batoid wing skeleton, including latitudinal stiffness, variation in types of ceratotrichia, and correlations between stiff areas of the wing and swimming mode, will give insight into ancestral swimming modes of batoids.

Nursery areas of the smalltooth sawfish in southwest Florida: implications for conservation

Fishing surveys, acoustic telemetry and public sightings data were used to identify and study nursery areas of the endangered smalltooth sawfish, Pristis pectinata. Public sighting data indicated that young juveniles (<90cm) occurred in many areas of Florida, with shallow protected estuarine habitats.identified as being the main habitat in which they occurred. Older juveniles (90 to 200 cm) occurred in a similar geographic range, but in a wider variety of habitats, to the young juveniles Fishing surveys using longlines and beach seines captured at least 15 juveniles, including four very young animals (approximately 80 cm). Six juveniles were fitted with acoustic tags and tracked to gather data on habitat use and residency time. The smallest juveniles showed strong preference for very shallow mud banks and other similar habitats, possibly to avoid predators such as bull sharks (Carcharhinus leucas) that occur nearby. Older juveniles occur in less protected habitats, but retain a preference for shallow estuarine areas. Older juveniles displayed long residency times in relatively small areas. The implications 23 of these results for conservation of the smalltooth sawfish population in US waters will be discussed.

Aspects of the life history and population structure of the diamond stingray, Dasyatis dipterura

Dasyatis dipterura (Jordan and Gilbert 1880; often inappropriately referred to as D. brevis) inhabits shallow, coastal waters from southern California to Peru, including the Galapagos and Hawaiian Islands. Although D. dipterura is a common component of artisanal elasmobranch fisheries and trawl fishery bycatch throughout western Mexico, very little is known of the life history of this stingray. Biological information was obtained from 1,119 fishery-derived specimens from the Magdalena Bay Lagoon Complex, Baja California Sur, Mexico. Sampling was conducted during 1998-2000 in four fishing camps. The sex ratio at the primary study site, Puerto Viejo, was 2.32:1 in favor of males in the 1998-99 landings (450 male:194 female; c2 0.05, 1 = 101.76). Specimen disc widths (DW) ranged from 25-89 cm, with females reaching greater sizes than males. Our largest recorded male measured 60 cm DW. Based on examination of reproductive tracts and clasper length-DW relationships in males, size-at-first-maturity was determined to be 45 and 57 cm DW for males and females, respectively. The average DW of females observed in the fishery was 52.1 cm, indicating that the majority of females landed in the fishery were immature. Growth characteristics were estimated by a detailed examination of banding patterns present in thin-sectioned vertebral centra. Age estimates were obtained from 358 specimens (160 male, 198 female). The maximum age, based on vertebral band counts, was 29 16.5 for males and 28 for females. Age-at-first maturity was determined to be 6-8 for males and 8-12 for females. Gompertz, logistic, and von Bertalanffy growth models were fit to the age-at- DW/weight data for the sexes combined and separately. The annual nature of band deposition was supported through centrum edge and marginal increment analyses. Von Bertalanffy growth parameters, empirical longevity, and mortality calculations will be presented and compared to published values obtained for other elasmobranchs.

Distribution, abundance, and reproductive status of skates landed in groundfish surveys off central California, USA

Although skates have long been a common component of bycatch and discard among eastern north Pacific trawl fisheries, very little is known of their biology, distribution, or abundance throughout this region. In California, landings of skates have markedly increased since the early 1990’s. Fishing pressure has notably impacted the abundance, population structure, and distribution of skates in the North Atlantic, emphasizing the need for baseline biological information of this poorly known group. Since September, 2002 members of the Pacific Shark Research Center have been working in cooperation with the National Marine Fisheries Service (NMFS), Santa Cruz Laboratory to investigate the life history, ecology, and systematics of central California skates. Data are being collected from monthly NMFS trawl surveys across five depth strata ranging from 18-823 m. We report on preliminary analyses of surveys conducted between September, 2002 and March, 2003. An approximate total of 1,500 specimens comprised of six species have been examined. The most abundant species, Raja rhina, comprised more than 50% of the overall catch followed by Bathyraja kincaidii, R. binoculata, R. inornata, and R. stellulata, respectively. Depth distribution and relative abundance of skates will be presented and compared by season, sex, reproductive status, and occurrence with the other chondrichthyans collected in these surveys.

A window of insight into Australian sawfishes through collection and husbandry for public aquaria

The collection of a variety of Australian Sawfishes for Public Aquaria provides valuable data and insights into these animals that would otherwise be difficult to obtain. Due to individual species preferring different habitat types, collection occurs through a broad range of areas. This results in substantial distances being covered to obtain the full variety of species present in Australia. Through holding and husbandry, both in the field and in a specialized facility situation, species specific traits (e.g., temperature ranges), can be observed that may assist in better understanding Australian sawfishes. This understanding combined with the data collected from DNA sampling and long term morphometric studies of these animals whilst in captivity, can assist in the development of relevant long term management of Pristids in Australia.

Additions to the skate fauna (Family Rajidae) of Alaska.

Skates of the genera Raja and Bathyraja constitute a significant proportion of the groundfish assemblages of the Gulf of Alaska, Aleutian Islands, and Bering Sea. Although these fishes are important components of both shallow and deepwater marine ecosystems in these regions, their populations have been inaccurately represented by fisheries monitoring programs due to difficulties in obtaining accurate species identification. As a result of collaborative efforts among taxonomists and fisheries biologists, recent NMFS bottom trawl surveys reflect great improvements in the reliability of skate identifications. A data set compiled from the catch records of NMFS bottom trawl surveys from 1999-2002, including the Gulf of Alaska, Aleutian Islands, and Eastern Bering Sea, gives a comprehensive overview of the skate fauna of Alaska. This data set includes a total of 13 recognized species of skates (3 species of Raja and 10 species of Bathyraja). In addition to these 13 recognized forms, as many as three undescribed forms of 41 Bathyraja have been discovered, and several other taxonomic questions have arisen. An overview of the skate fauna of Alaska will be presented, along with an introduction to one new form and an outline of future research directions.

Shark management in the United States Atlantic Ocean: status, challenges, and options

The Highly Migratory Species (HMS) Management Division of the National Marine Fisheries Service (NOAA Fisheries) has initiated development of Amendment 1 to the Fishery Management Plan (FMP) for Atlantic tunas, swordfish, and sharks based on the results of the 2002 stock assessments of large coastal sharks (LCS) and small coastal sharks (SCS). The amendment will establish rebuilding plans for overfished shark stocks and actions to prevent overfishing of other shark stocks. The amendment will also address concerns regarding bycatch of protected and prohibited species and exempted fishing permit processes. Challenges facing domestic Atlantic shark management include the need to improve knowledge of essential fish habitat, the lack of a current stock assessment for pelagic sharks, the lack of detailed biological data for some species, the demand for increased observed coverage, as well as widespread problems with species-specific identification and the subsequent problems confounding 42 species-specific management. The options in the rule will be based on the 2002 LCS and SCS stock assessments as well as comments received during public meetings held in February and March of 2003. Management options include, but are not limited to, quotas, trip limits, methods to account for mortality, time and area closures, recreational retention limits, gear limitations, and landing requirements.

Under pressure to swim fast: shark myotomal pressure increases with increasing swimming speed

High speed swimming requires a stiff body to maximize thrust delivered along the main axis of the fish. Swiftly swimming bony fishes have few vertebrae (e.g. 22 in marlins), and have substantial bony zygapophyses that span the intervertebral joints. This results in a very stiff vertebral column, which provides the requisite whole-body stiffness. Some sharks are remarkably fast swimmers, yet they have a large number of discoidal vertebrae (180 precaudal in the mako shark) that seem ill-suited to resisting flexion. In order to obtain a better understanding of the ways in which fish with cartilaginous skeletons perform at levels similar to fishes with bony skeletons, we tested the hypothesis that sharks can dynamically change internal body pressure during locomotion. We implanted pressure transducers in the epaxial musculature of spiny dogfish sharks and swam them in a flow tank at speeds from 0.25 to 1.75 body lengths per second. The myomeric pressure varied sinusoidally over the course of the tail beat cycle, from subambient to superambient, attaining peaks at the extremes of body curvature Contralateral pressures were 180 degrees out of phase. Intramuscular pressure increased significantly with speed, suggesting a possible mechanism for increasing body stiffness for high-speed swimming. We expect that faster-swimming sharks such as makos and great whites will be pressurized to a greater extent.

Behavior and ecology of the lemon shark (Negaprion brevirostris): a review

Despite the wide public attention given to sharks, surprisingly little is known of their behavior and ecology. One exception is the lemon shark, where over 40 years of laboratory and field research have revealed detailed information on many aspects of its life history and biology. Of the known sensory modalities possessed by sharks, the visual and auditory systems in the lemon shark have been well investigated. The morphology and electrophysiology of the 46 olfactory organ is described, while only scarce data are available for electroreception and the gustatory, magnetic, tactile, thermal and other senses. The intensively studied populations of lemon sharks in Florida Keys and Bimini Islands, Bahamas have provided detailed information on ecology, behavior and bioenergetics, including metabolic requirements, consumption rates, prey species, and conversion efficiencies in juvenile.sharks, which in combination with laboratory findings has allowed for the balancing of bioenergetics equations for both small and large juveniles. Spatial and temporal behavior has been investigated using ultrasonic telemetry in conjunction with measurements of environmental parameters. Life-history traits such as litter size, survival rate, age at maturity, and reproductive rates as well as recent information derived from molecular research on mating systems, population dynamics and population structure, are helping us understand the overall ecology and conservation status of the species. Such information is also important when assessing a population’s resistance to environmental change or estimating recovery time after devastation of local populations. However, the ecology and behavior of adults remains an enigma and we believe that this is where future effort should be concentrated.

A metapopulation model for spiny dogfish (Squalus acanthias) in the Northeast Pacific

The spiny dogfish is the most abundant shark species in the Northeast Pacific and occurs primarily in coastal waters from Mexico to Alaska. Tagging studies have shown both coastwide and trans-pacific migrations. A transboundary fishery in British Columbia and Washington State has had strong variation in effort over its 130 year history, with a peak in 1944 which has not been matched since. The primary stock assessment of spiny dogfish in Northeast Pacific was based upon a demographic model which relied on ageing techniques, since revised, and did not incorporate indices of abundance. A more recent multispecies spatial model which used Canadian trawl CPUE found evidence of depletions in some parts of British Columbia. Indices of abundance in all areas are highly uncertain, but trawl surveys in the Puget Sound indicate reduced numbers while adjacent, coastal surveys indicate a relatively stable population size. The migrations between these areas with differing population trends suggest the modeling of spiny dogfish as a metapopulation. This paper describes a metapopulation model built to incorporate the many varied and patchy sources of data on spiny dogfish in the Northeast Pacific. We use it to evaluate hypotheses regarding stock structure and rates of mixing between areas, as well as abundance and population trends within each area. This is the first attempt to estimate the changes in abundance of this species over either the history of commercial exploitation or the greater part of its range in the Northeast Pacific.

2002 survey of sawfish populations in rivers and estuaries of northern Australia

The freshwater sawfish Pristis microdon is listed as vulnerable on the Commonwealth endangered species act, and there is considerable concern over the population status of the other species of sawfish in Australia. In 2002, a cooperative study between CSIRO Marine Research, Universities, Museums and fisheries agencies of Western Australia, the Northern Territory and Queensland surveyed river systems across the north of the continent. The sampling strategy was affected by the logistics of covering remote and often inaccessible country and was limited to the dry season between May and November. Fishing was carried out mainly using a combination of longlines and gillnets with different mesh sizes and we attempted to sample from upstream habitats such as isolated pools or billabongs down into the estuarine reaches and at times, the coastal margins. Deployment times of fishing gear were kept as short as practical to minimise mortalities. Pristis microdon, P. clavata and Onoxypristis cuspidata were caught during the survey. Other chondrichthyans caught in freshwater were Carcharhinus leucas and Himantura chaophraya. While no Glyphis spp. were caught during the survey, one specimen was captured in the Kimberley region by an associated project team. The greatest number of P. microdon captured in freshwater areas were taken in the Kimberley region of Western Australia.

A tale of two ovaries: reproduction in the salmon shark (Lamna ditropis)

The salmon shark (Lamna ditropis) is an apex predator in the North Pacific Ocean. The population dynamics of this species is important for biological and management reasons. In order to understand salmon shark population dynamics in the North Pacific, basic biological traits must be characterized. An understanding of the natural history of the salmon shark, including the reproductive cycle is central to the estimation of demographic parameters for conservation and management. Most of the existing literature about this species is based on the animal’s appearance as by-catch in salmon gill nets in the western North Pacific until the early 1980’s. However, the salmon shark is highly migratory and these studies cover only a slice of the reproductive cycle. The current study is one of the few focused on reproductive biology. Results are based upon samples from Prince Williams Sound and other locations across the North Pacific Ocean. Research objectives are: estimate size of maturity, seasonality of reproductive events and to study other physiological characteristics of salmon shark reproduction. This is accomplished by examinations of the reproductive tracts, analysis of serum reproductive hormone concentrations and examination histological tissue sections. Results thus far suggest mating by pubescent females and size at maturity, apparent differences in oviductal gland structure pre and post puberty, and anatomical correlations with reproductive hormone concentrations.

Determination of reproductive parameters of chondrichthyan animals for population assessment

Determination of the annual birth rate of a population of chondrichthyan animals requires two mathematical relationships. One expresses the proportion of the female population in maternal condition as a function of size or age of animal, and the other expresses fecundity as a function of maternal size or age. Incorrect application in demographic analysis or in fishery stock assessment of size- or age-at-maturity ogives or of size- or age-at-pregnancy ogives, instead of size- or age-at-maternity ogives, often causes.marked over-estimation of birth rate. Explicit definitions of maturity, pregnancy, and maternity are compared. Logistic regression methods are presented for determination of appropriate parameters and for statistically testing for spatial and temporal effects on these parameters. Various methods for determining male length-at-maturity are evaluated. Spatial and temporal differences in reproductive parameters are illustrated by Mustelus antarcticus, Galeorhinus galeus, Pristiophorus cirratus, and Callorhinchus milii in southern Australia from samples collected during three separate periods (1973-76, 1986-87, and 1998-01). The hypothesis for the phenomenon of apparent change in size-at-maternity (and size-at-maturity) caused by gillnet length-selective fishing mortality is favoured to explain observed increases in length-at-maternity (and length-at-maturity) following periods of intensive fishing.

Aspects of the biology of Goblin sharks collected from the Tokyo Submarine Canyon, Japan

The goblin shark, Mitsukurina owstoni, is a large, rare species from deep water that is distinguished from all other sharks by the combination of its flat, bladelike, elongated snout, very long-cusped teeth, and long caudal fin that lacks a ventral lobe. Sixty-five males (817-2085 mm TL) and 56 females (928-1961 mm TL) were examined for morphometric growth patterns, distribution, stomach contents and reproductive condition. The specimens were collected via bottom gill nets along a steep slope of the Tokyo Submarine Canyon (100-350 m depth). A bottom gill net fishery in the steep slope areas of the Canyon began relatively recently, and thus provided many specimens of M. owstoni for the present study. The allometric size-on-size equation Y=aXb was used to determine morphometric growth patterns, positive allometry, negative allometry, and isometry. Goblin sharks were abundant between December and April at around 250 m depth. No specimen examined was sexually mature, including the largest male (2085 mm TL) and female (1961 mm TL) specimens examined. Stomachs from 121 specimens were analyzed; of these, 43 stomachs (35.5%) were empty. Prey items included teleost fishes, squids, decapods, isopods and digested food. Teleost fishes consisting of Macrouridae sp. and Stomiidae spp., and decapods consisting of Pasiphaea sinensis and Sergia sp. were the only identifiable prey in the stomachs of M. owstoni examined. The stomach contents in this study suggest that M. owstoni consumed, in order of importance, teleost fishes.