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Skates have become a concern in recent years due to the preponderance of these elasmobranchs that are caught as bycatch or as a directed fishery. This has raised concern because skates have life history characteristics that may make them vulnerable to over-exploitation. It was due to this increasing awareness and concern about these batoids that prompted us to organize an international symposium on the “ Biology of Skates”. The aims and goals of the symposium were to bring together an international group of researchers to meet, discuss, perhaps develop collaborations, and present their most recent findings. The symposium was held over two days, on 13–14 July, 2006, in conjunction with the 22nd annual meeting of the American Elasmobranch Society in New Orleans, LA. A total of 31 authors from four countries contributed 16 papers that appear in this special issue. The papers are broadly arranged into four separate categories: systematics and biogeography, diet and feeding ecology, reproductive biology, and age and growth. To the best of our knowledge this is the first dedicated book on the biology of skates. We hope that readers will find this issue of interest and that it helps encourage and stimulate future research into these fascinating fishes. [ABSTRACT FROM AUTHOR]

Summary: Length–weight relationship (LWR) was estimated for 12 elasmobranch species; five shark species, four species of rays and three species of guitar fishes from north‐eastern Arabian Sea, India. Five major landing centres of Maharashtra were selected; Satpati (Lat. 19°43′15″N, Long. 72°42′00″E), Naigaon (Lat. 19°19′32″N, Long. 72°48′54″E), Versova (Lat. 19°08′33″N, Long. 72°48′11″E), New ferry Wharf (Lat. 18°57′29″N Long. 72°51′01″E) and Sassoon dock (Lat. 18°54′42″N, Long. 72°49′33″E). Samples were collected fortnightly during August 2016 to October 2017 from various gears; drift gill nets (Hung length 114–143 m and #100–270 mm) off Satpati coast at 35–50 m depth, dol nets (length 50–65 m and cod end # 30–69 mm) in Naigaon at 38–50 m depth and trawl (length 33–72 m and cod end # 17–32 mm) in Versova, New ferry Wharf and Sassoon dock operated at 20–50 m depth. Multiday fishing was carried out with 2–3 fishing trips in a month, each trip with duration of 7–13 days. Soaking time of gill net and dol net varied from 4 to 8 hr while each trawl haul lasted for 3–4 hr. Length–weight/Disc‐width‐weight relationship showed good fit with r2 values varying from 0.818 to 0.999. In addition to information on LWR, new maximum size for three species of elasmobranchs is reported in this paper. [ABSTRACT FROM AUTHOR]

Abstract  The biology of elasmobranchs makes them very vulnerable to fishing pressure and there is increasing international concern over their exploitation. In northern Australia the stocks of some species may be shared with those in southern Indonesia. Indonesia has the highest landings of elasmobranchs worldwide (>100,000 t p.a.) and millions of Indonesian artisanal fishers rely heavily on elasmobranchs taken in target fisheries. They are also taken by industrial trawlers and as bycatch in pelagic tuna fisheries. This paper, resulting from a collaborative project between Australia and Indonesia, summarises the elasmobranch fisheries; the characteristics of the fisheries are outlined, the status of the stocks are assessed, and management options described and discussed. The project focussed on representative markets and fish landing sites in southern Indonesia from 2001 to 2005. Data were from market surveys, the records of the Indonesian Directorate General of Capture Fisheries, and from research cruises. Data from the ongoing tuna monitoring programme showed that shark bycatch from the tuna fleets forms about 11% of shark landings in Indonesia. Yield per recruit and related analyses were used to integrate biological information to indicate the productivity of each species to allow for management policy options and constraints. Research cruise data show that catch rates of elasmobranchs in the Java Sea declined by at least one order of magnitude between 1976 and 1997. The results indicate strongly that many of the shark and ray species in Indonesia are overfished and that the most effective management strategy may need to involve capacity control, such as licencing, gear restrictions and catch limits, together with controls on the fin trade. [ABSTRACT FROM AUTHOR]

This paper supplements former studies on elasmobranch species with an immunohistochemical investigation into glutamine synthetase and S-100 protein, in addition to GFAP, and extends its scope to the representatives of almost every group of Elasmobranchii: squalomorph sharks, galeomorph sharks, skates (Rajiformes) and rays (Torpediniformes and Myliobatifomes). More glial elements were labeled by S-100 protein, and even more so by using glutamine synthetase immunostaining than by GFAP: more astrocytes (mainly non-perivascular ones) were detected in the telencephalon of sharks, skates and rays. Only the markers S-100 and glutamine synthetase, but not GFAP, characterized the Bergmann-glia of skates and rays and astrocyte-like non-ependymal cells in Squalus acanthias. Another squalomorph shark species, Pristiophorus cirratus, however, had GFAP immunopositive astrocytes. Of all the species studied, the greatest number of GFAP positive astrocytes could be observed in Mobula japanica (order Myliobatiformes), in each major brain part. According to anatomical location, perivascular glia comprised varied types, including even a location in Mobula, which can also be found in mammals. Remnants of radial glia were found in confined areas of skates, less so in rays. In the rhombencephalon and in the spinal cord modified ependymoglia predominated in every group. In conclusion, there was no meaningful difference between the astroglial architectures of squalomorph and galeomorph sharks. The difference in the astroglial structure between sharks and batoids, however, was confined to the telencephalon and mesencephalon, and did not take place in the rhombencephalon, the latter structure being quite similar in all the species studied. The appearance of astrocytes in the relatively thin-walled shark telencephalon, however, indicates that the brain thickening promoted the preponderance of astrocytes rather than their appearance itself. Although the evolutionary changes of astroglia had some similarities in Elasmobranchii and Amniota, there was one meaningful difference: in Elasmobranchii astrocytes did not prevail in conservative brain regions as they did in the progressive brain regions. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Background: GTPase-activating proteins (GAPs) with a TBC (Tre-2/Bub2/Cdc16) domain architecture serve as negative regulators of Rab GTPases. The related crystal structure has been studied and reported by other members of our research group in 2017 (Chen et al. in Protein Sci 26(4):834–846, 2017). The protein crystal structure and sequencing data accession numbers in Protein structure database (PDB) are 5TUB (Shark TBC1D15 GAP) and 5TUC (Sus TBC1D15 GAP), respectively. In this paper, we analyzed the Rab-GAP specificity of TBC1D15 in the evolution and influence of key amino acid residue mutations on Rab-GAP activity. Results: Sequence alignment showed that five arginine residues of the TBC1D15-GAP domain are conserved among the species Sus/Mus/Homo but have been replaced by glycine or lysine in Shark. A fragment activity assay was conducted by altering the five residues of Shark TBC1D15-GAP to arginine, and the corresponding arginine in TBC1D15 GAP domains from Sus and Homo species were mutated to resemble Shark TBC1D15-GAP. Our data revealed that the residues of G28, K45, K119, K122 and K221 in the Shark TBC1D15-GAP domain had a key role in determining the specificity for Rab7 and Rab11. Mutation of the five residues significantly altered the Shark TBC1D15-GAP activity. Conclusions: These results revealed that the substrate specificity of TBC1D15 has had different mechanisms across the evolution of species from lower-cartilaginous fish to higher mammals. Collectively, the data support a different mechanism of Shark TBC1D15-GAP in substrate selection, which provides a new idea for the development of Marine drugs. [ABSTRACT FROM AUTHOR]

A specimen of Holohalaelurus shark (Scyliorhinidae; Chondrichthyes) recently collected off southern Mozambique, represents a southward range extension of 2200krn for the recently described, H. grennian Human 2006. This specimen presents not only a significant extension of its known distribution, but is also only the second female specimen known for this species. Moreover, the specimen exhibits morphological characters, particularly colouration, which are more typically attributed to congeners occurring in the southern part of its range. This paper is an account of the range extension for H. grennian, and compares the morphological and colouration differences in this specimen compared to the original species description. A shape analysis is conducted on the specimen, and a revised zoogeography of the genus Holohalaelurus is presented. [ABSTRACT FROM AUTHOR]

The paper deals with a new record of the juvenile sandbar shark Carcharhinus plumbeus (Nardo, 1827) in the waters off Piran. This record confirms again the fact that the northern Adriatic Sea should be considered as a nursery area for this species. This fact, together with the general lack of knowledge on other shark species, show the need for systematic research of elasmobranch populations in the Slovenian part of the Gulf of Trieste. [ABSTRACT FROM AUTHOR]

Validated age and growth estimates are important for constructing age-structured population dynamic models of chondrichthyan fishes, especially those which are exploited. We review age and growth studies of chondrichthyan fishes, using 28 recent studies to identify areas where improvements can be made in describing the characteristics of ageing structures (both traditional and novel) utilized to estimate ages of sharks, rays, and chimaeras. The topics identified that need consistency include the: (1) terminology used to describe growth features; (2) methods used to both verify and validate age estimates from chondrichthyan calcified structures, especially edge and marginal increment analyses; and (3) the functions used to produce and describe growth parameters, stressing the incorporation of size at birth ( L 0) and multiple functions to characterize growth characteristics, age at maturity and longevity. [ABSTRACT FROM AUTHOR]

The biogeography and conservation of elasmobranch species was increasingly addressed in the recent past, but the southwestern Atlantic Ocean fauna is still one of the least studied. Reliable delimitation of the distribution range of species is fundamental to conservation and development of fisheries management strategies. A recent molecular study of the cryptic Aetobatus narinari species complex restricted that species to western and eastern coasts of the New World. However, the current distribution of A. narinari and phylogenetic relationships within the genus Aetobatus have yet to be clarified, the goal of this phylogeographic analysis. Using mitochondrial and nuclear markers we investigated specimens from the Atlantic coast of Brazil and the Pacific coast of Mexico and related them to previously analyzed specimens from other regions. Our analysis indicates that Aetobatus narinari is present only in the western Atlantic, formed by a single genetic lineage that ranges between Florida and southeastern Brazil, while the Pacific New World lineage is in fact assigned to Aetobatus laticeps. Analysis of divergence times revealed that biogeographic events such as the closure of the Tethys Sea, the formation of the Benguela barrier, and the Isthmus of Panama played major roles in diversification and dispersal of the genus Aetobatus. [ABSTRACT FROM AUTHOR]

Developing nations in tropical regions harbour rich biological resources on which humans depend for food, income and employment, yet data to aid their management is often lacking. In West Africa, the diversity and fisheries of elasmobranchs are poorly documented, despite them being known to be economically important and vulnerable to overexploitation. Rapid qualitative surveys of fish processing and landing sites in The Gambia from 2010-2018 revealed valuable new data on species composition, biology, relative abundance, fisheries and utilisation by humans. Diversity and abundance was dominated by batoids, with a major component comprising a large guitarfish (Glaucostegus cemiculus) that was apparently targeted, and a small whipray (Fontitrygon margaritella). Nearly all taxa recorded are classified by the IUCN Red List as Critically Endangered (angel sharks Squatina spp.), Endangered, Data Deficient, or Not Evaluated; several were endemic, of exceptional evolutionary distinctness, cryptic, possibly undescribed, and rare (including stingray Hypanus rudis not apparently recorded since description in 1870). Significant threats to biodiversity, coastal livelihoods and possibly food security are identified based on the apparent importance of elasmobranch fisheries and processing; the known inability of key taxa to withstand intensive fisheries; 'fishing down the food web' by intensive utilisation of F. margaritella; and the absence or rarity of previously common elasmobranch species that may be severely depleted in the region. This study provides data that may act as a starting point to aid sustainability accreditation of local fin-fisheries, and demonstrates the value of inexpensive and low-resolution data collection in developing countries. [ABSTRACT FROM AUTHOR]

The fate of bycatch species released back into the water is crucial to estimate population status and consequent decisions to implement adequate management measurements for elasmobranchs. The shortnose guitarfish, Zapteryx brevirostris, is an endemic species of the Southwest Atlantic. It is currently listed as 'Vulnerable' both in the International Union for Conservation of Nature and Brazilian red lists. Although this species displays high tolerance to capture and transportation by fishers from the capture site to the fish market, a significant reduction in survival rates is observed during the reproductive period. Thus, the aim of the present study was to examine post‐capture and post‐commercial transportation consequences in pregnant females obtained as bycatch from artisanal fisheries in Southern Brazil. Results showed high abortion rates and reduced maternal survival after abortion, with all abortions occurring within 28 h of monitoring in laboratory. Stress plasma markers were also evaluated, to determine the physiological consequences of capture‐induced parturition to pregnant females. Results showed alteration in all markers measured (plasma urea, pH, lactate, phosphorus, and potassium) with values for dead pregnant females being different from non‐pregnant females and those which survived capture and subsequent abortions. The mortality caused by fisheries bycatch may prove difficult to manage, with immediate release and specific handling protocols for pregnant females implemented through environmental education environmental education and fishermen training programs, potential options to maintain adequate maternal survival and recruitment for this species. There is a growing concern about elamobranch overfishing worldwide, as well as an urgent need for the implementation of containment plans for bycatch, representing a very significant volume of annual catches for batoids and sharks. This study provides new information to understand the impact caused by incidental capture in an endemic and threatened guitarfish, suggesting practices to assist with satisfactory management plans for the shortnose guitarfish, Zapteryx brevirostris, especially during their reproductive season. [ABSTRACT FROM AUTHOR]

The present study analysed the condition factor (K) and the hepato‐somatic index (IH) of the Brazilian sharpnose shark Rhizoprionodon lalandii during its entire life cycle. Discontinuity of liver growth was observed after sexual maturity. High condition values were recorded in the length classes of 300–350 mm (neonates), when the livers represented about 8% of total mass, decreasing until the length classes of 400–450 and 450–500 mm in females and males, respectively. Seasonal analysis exhibited low IH values in the summer, while for K, low values were in spring, indicating greater investment for body growth during spring and for gonad maturation in summer. Such findings indicate that this small coastal shark species accumulates reserve substances in the liver that will be used during reproduction. The decline in IH values in juveniles suggests that reserves provisioned by the mother to the neonate liver can be used in the first months of life. [ABSTRACT FROM AUTHOR]

Elasmobranchs are among the most threatened long-lived marine species worldwide, and incidental capture is a major source of mortality. The northern central Adriatic Sea, though one of the most overfished basins of the Mediterranean Sea, supports a very valuable marine biodiversity, including elasmobranchs. This study assesses the impact of the northern central Adriatic pelagic trawl fishery on common smooth-hound (Mustelus mustelus), spiny dogfish (Squalus acanthias), common eagle ray (Myliobatis aquila), and pelagic stingray (Pteroplatytrygon violacea) by examining incidental catches recorded between 2006 and 2015. The distribution of bycatch events was evaluated using geo-referenced data. Generalized Linear Models were computed to standardize the catch of the four species and to predict the relative abundance of bycatch events. Data analysis shows that most bycatch events involving all four species occurred in the northern Adriatic Sea. The models predicted significant, distinct temporal patterns of standardized catches in line with previous investigations. Water depth, season, and fishing region were the best predictors to explain bycatch events. The present data suggest that the northern Adriatic may be an important nursery area for several elasmobranchs. They also highlight the urgent need for a better understanding of the interactions between elasmobranchs and fisheries to develop and apply suitable, ad hoc management measures. [ABSTRACT FROM AUTHOR]

As upper level predators, sharks serve an important role in marine ecosystems, but are often at risk from fisheries. Successful management of these species will require detailed information about their movements and distributions., Using satellite telemetry, we investigated the long-term horizontal movements and seasonal distributions of shortfin mako sharks Isurus oxyrinchus in the western North Atlantic Ocean., Twenty-six sharks (14 USA, 12 Mexico) were tracked for durations of 78-527 days. Ten sharks were tracked for >1 year. Sharks displayed region-specific movements, with little distributional overlap between the Gulf of Mexico and Caribbean Sea, and the western North Atlantic. Sharks tagged off the USA ranged over a larger area, including shelf and pelagic habitats. Their core distribution was largely over the continental shelf and fluctuated seasonally, ranging from South Carolina, USA, in the winter to Nova Scotia, Canada, in the autumn, and appeared to follow seasonal productivity peaks while favouring warmer waters. Sharks tagged off Mexico displayed more restricted movements, largely confined to shelf habitats, with core activity centred year-round on the eastern Campeche Bank, Mexico., Sharks moved across the jurisdictional management boundaries of 17 nations, and the proportion of tracked sharks harvested (22%) was twice that obtained from previous fisheries-dependent, conventional tagging studies., Sharks also displayed considerable variability in movements, with seven sharks tagged off the USA making long-distance, highly directional southern excursions into unproductive subtropical/tropical waters before returning north., Policy implications. The large-scale and region-specific movements of shortfin mako sharks underscore the need for close cooperation amongst western North Atlantic nations and implementation of regionally and seasonally specific management strategies. The movement patterns also provide baseline information, which could be used in spatially explicit stock assessment models. Identification of high-use areas by shortfin mako sharks provides focal areas for quantifying interactions with fisheries. The high harvest rate observed in our fisheries-independent tracking study raises questions about the true rate of fisheries mortality experienced by shortfin mako sharks, calling for a cautionary interpretation of past stock assessments used to determine management policy for this highly migratory species of conservation concern. [ABSTRACT FROM AUTHOR]

The Arabian Seas Region plays an important role in the global landings and trade of sharks and rays. The United Arab Emirates ( UAE) and Yemen, two countries with stark socio-economic differences, serve as major regional trade hubs for shark and ray products and four countries (Oman, Pakistan, UAE and Yemen) supply nearly 11% of dried fin exports to Hong Kong. Yet, little information is available on the characteristics of this trade and the fisheries contributing to it. Here, we review the fisheries characteristics, trade, utilization and distribution chain of sharks and rays in 15 countries of the Arabian Seas Region based on published and grey literature, landing surveys, field observations and interviews with fishermen and traders. Although regional shark fisheries remain mostly artisanal, reported shark and ray landings represent 28% of the regional total fish production, reaching 56,074 mt in 2012 (7.3% of total world catches), with Iran, Oman, Pakistan and Yemen ranking as the primary catchers. Utilization and distribution patterns are complex, vary between landing sites and countries, and remain unmonitored. Based on widespread over-exploitation of most teleost fisheries, current exploitation levels for most sharks and rays are potentially unsustainable. The situation is exacerbated by limited research and political will to support policy development, the incomplete nature of fisheries data, as well as insufficient regulations and enforcement. A better understanding of shark and ray fisheries will be key for regulating trade, promoting conservation and developing management initiatives to secure food security, livelihoods and biodiversity conservation in the region. [ABSTRACT FROM AUTHOR]

Pelagic longline fisheries for relatively fecund tuna and tuna-like species can have large adverse effects on incidentally caught species with low-fecundity, including elasmobranchs., Analyses of observer programme data from the Fiji longline fishery from 2011 to 2014 were conducted to characterize the shark and ray catch composition and identify factors that significantly explained standardized catch rates. Catch data were fitted to generalized linear models to identify potentially significant explanatory variables., With a nominal catch rate of 0.610 elasmobranchs per 1000 hooks, a total of 27 species of elasmobranchs were captured, 48% of which are categorized as Threatened under the IUCN Red List. Sharks and rays made up 2.4% and 1.4%, respectively, of total fish catch. Blue sharks and pelagic stingrays accounted for 51% and 99% of caught sharks and rays, respectively., There was near elimination of 'shark lines', branchlines set at or near the sea surface via attachment directly to floats, after 2011., Of caught elasmobranchs, 35% were finned, 11% had the entire carcass retained, and the remainder was released alive or discarded dead. Finning of elasmobranchs listed in CITES Appendix II was not observed in 2014., There were significantly higher standardized shark and ray catch rates on narrower J-shaped hooks than on wider circle hooks. Based on findings from previous studies on single factor effects of hook width and shape, the smaller minimum width of the J-shaped hooks may have caused the higher shark and ray catch rates. For sharks, the effect of hook width may have exceeded the effect of hook shape, where small increases in shark catch rates have been observed on circle vs J-shaped hooks., Shark and ray standardized catch rates were lowest in the latter half of the year. Focusing effort during the second half of the year could reduce elasmobranch catch rates., Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Tuna fisheries have been identified as one of the major threats to populations of other marine vertebrates, including sea turtles, sharks, seabirds and marine mammals. The development of technical mitigation measures (MM) in fisheries is part of the code of conduct for responsible fisheries. An in-depth analysis of the available literature regarding bycatch mitigation in tuna fisheries with special reference to elasmobranchs was undertaken. Studies highlighting promising MMs were reviewed for four tuna fisheries (longline, purse seine, driftnets and gillnet, and rod and line - including recreational fisheries). The advantages and disadvantages of different MMs are discussed and assessed based on current scientific knowledge. Current management measures for sharks and rays in tuna Regional Fishery Management Organizations (t-RFMOs) are presented. A review of relevant studies examining at-vessel and postrelease mortality of elasmobranch bycatch is provided. This review aims to help fisheries managers identify pragmatic solutions to reduce mortality on pelagic elasmobranchs (and other higher vertebrates) whilst minimizing impacts on catches of target tuna species. Recent research efforts have identified several effective MMs that, if endorsed by t-RFMOs, could reduce elasmobranchs mortality rate in international tropical purse seine tuna fisheries. In the case of longline fisheries, the number of operational effective MMs is very limited. Fisheries deploying driftnets in pelagic ecosystems are suspected to have a high elasmobranchs bycatch and their discard survival is uncertain, but no effective MMs have been field validated for these fisheries. The precautionary bans of such gear by the EU and by some t-RFMOs seem therefore appropriate. Recreational tuna fisheries should be accompanied by science-based support to reduce potential negative impacts on shark populations. Priorities for research and management are identified and discussed. [ABSTRACT FROM AUTHOR]

Estimated declines in shark and ray populations worldwide have raised major, widespread concern about the impacts of global fisheries on elasmobranchs. The mechanisms causing elasmobranch mortality during fisheries' capture are not fully understood, but we must gain greater clarity on this topic for fisheries managers to develop effective conservation plans to mitigate further population declines. To evaluate how two important factors, respiratory mode and fishing gear type, impact elasmobranch survival, we compiled publicly available data sources on the immediate mortality percentages of 83 species and post-release mortality percentages of 40 species. Using Bayesian models, we found that sharks and rays captured in longlines had significantly lower immediate mortality than those caught in trawls or gillnets. Our models also predicted the mean total discard mortality (combined immediate and post-release mortality) percentages of obligate ram-ventilating elasmobranchs caught in longline, gillnet and trawl gear types to be 49.8, 79.0 and 84.2%, respectively. In contrast, total discard mortality percentages of stationary-respiring species were significantly lower (longline capture mean = 7.2%, gillnet capture mean = 25.3%, trawl capture mean = 41.9%). Our global meta-analysis provides the first quantified demonstration of how mortality is affected by these two factors across a broad range of species. Our results and approach can be applied to data-deficient elasmobranchs and fisheries to identify species that are likely to experience high rates of mortality due to respiratory mode and/or fishing methods used, so that appropriate mitigation measures can be prioritized and investigated. [ABSTRACT FROM AUTHOR]

Global chondrichthyan (shark, ray, skate and chimaera) landings, reported to the United Nations Food and Agriculture Organization ( FAO), peaked in 2003 and in the decade since have declined by almost 20%. In the FAO's 2012 'State of the World's Fisheries and Aquaculture' report, the authors 'hoped' the reductions in landings were partially due to management implementation rather than population decline. Here, we tested their hypothesis. Post-peak chondrichthyan landings trajectories from 126 countries were modelled against seven indirect and direct fishing pressure measures and eleven measures of fisheries management performance, while accounting for ecosystem attributes. We found the recent improvement in international or national fisheries management was not yet strong enough to account for the recent decline in chondrichthyan landings. Instead, the landings declines were more closely related to fishing pressure and ecosystem attribute measures. Countries with the greatest declines had high human coastal population sizes or high shark and ray meat exports such as Pakistan, Sri Lanka and Thailand. While important progress had been made, country-level fisheries management measures did not yet have the strength or coverage to halt overfishing and avert population declines of chondrichthyans. Increased implementation of legally binding operational fisheries management and species-specific reporting is urgently required to avoid declines and ensure fisheries sustainability and food security. [ABSTRACT FROM AUTHOR]

The skeleton of cartilaginous fishes is notoriously difficult to prepare, and the literature dealing with the subject is extremely rare compared to other vertebrate groups. As a result, chondrichthyan skeletal specimens held in museums and other scientific institutions are often limited to isolated sets of jaws, taxidermised specimens and small individuals preserved whole in fluid. However, skeletal characters are heavily relied upon in several taxonomical and phylogenetical analyses, highlighting the importance of properly prepared skeletal specimens in research collections. The relevant literature is briefly reviewed herein, with a proposal for a new and simple protocol involving limited and easily obtainable chemicals, for the quick preparation of clean and durable chondrichthyan skeletal specimens. Various features of the chondrichthyan skeleton are also discussed, along with the microstructural effects of the chemicals involved in the protocol. [ABSTRACT FROM AUTHOR]

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Large pelagic sharks are distributed throughout all of the oceans and are caught as bycatch in pelagic longline fisheries worldwide. In the southern Atlantic Ocean, more than a dozen shark species are caught by the Brazilian tuna longline fleet. This study compiles information of the main shark species caught by the Brazilian tuna longline fishery in the southwestern and equatorial Atlantic Ocean. Catch and effort data of 14,860 longline sets from the Brazilian chartered tuna longline fleet, between 2004 and 2010, were analyzed. The blue shark Prionace glauca was the main shark species captured by this fishery. Shark catches showed contrasting trends during the study period: the silky ( Carcharhinus falciformis) and the oceanic whitetip ( C. longimanus) sharks catch increased up to 2008 and then declined, while mako sharks ( Isurus spp.) showed an opposite trend. Effort for the Brazilian longline fishery had a higher concentration from 10°N to 30°S and from 20°W to 40°W. High values of catch per unit effort of southwestern and equatorial Atlantic Ocean sharks were heterogeneously distributed and, although elasmobranchs were caught over most of the longline fishing range, only blue sharks were caught in all areas. In the southern Atlantic Ocean, high fishing effort zones overlap significantly with some nursery areas, especially for the oceanic whitetip shark, indicating that these areas are at a direct risk from the industrial longline fishery. [ABSTRACT FROM AUTHOR]

By-catch in marine fisheries, particularly those using pelagic and demersal longlines, is a major driver of declines in abundance of sharks and rays around the world. A wide variety of by-catch reduction devices ( BRDs), that is, modified gears designed to reduce incidental captures of a variety of marine species while maintaining target catch rates, have been proposed, but the extent to which BRDs actually reduce the risk of catching sharks and rays remains unclear. We performed a meta-analysis of 27 publications that reported the capture of sharks and rays and, in some cases, of targeted teleosts in longline gear deployed with and without BRDs. The risk of shark and ray capture differed between types of BRDs, but only one BRD type, longlines raised off the bottom, reduced by-catch significantly. Circle hooks did not reduce the risk of capturing sharks and rays but might improve discard survival and are inexpensive, which might make them effective in reducing the detrimental effects of longlining on these species. In addition to being generally ineffective, some devices, such as electropositive and magnetic repellents, are expensive and have inherent construction drawbacks that are likely to make them unsuitable for commercial use. Overall, most BRDs did not affect the likelihood of catching targeted teleosts, but a substantial number of studies did not adequately assess target catch. We identified two poorly studied classes of BRD gear (i.e. raised demersal longlines, and monofilament nylon leaders), which represent promising directions for future research. [ABSTRACT FROM AUTHOR]

The hypothalamus has been a central topic in neuroanatomy because of its important physiological functions, but its mature organization remains elusive. Deciphering its embryonic and adult organization is crucial in an evolutionary approach of the organization of the vertebrate forebrain. Here we studied the molecular organization of the hypothalamus and neighboring telencephalic domains in a cartilaginous fish, the catshark, Scyliorhinus canicula, focusing on ScFoxg1a, ScShh, ScNkx2.1, ScDlx2/5, ScOtp, and ScTbr1 expression profiles and on the identification α-acetylated-tubulin-immunoreactive (ir), TH-ir, 5-HT-ir, and GFAP-ir structures by means of immunohistochemistry. Analysis of the results within the updated prosomeric model framework support the existence of alar and basal histogenetic compartments in the hypothalamus similar to those described in the mouse, suggesting the ancestrality of these subdivisions in jawed vertebrates. These data provide new insights into hypothalamic organization in cartilaginous fishes and highlight the generality of key features of the prosomeric model in jawed vertebrates. [ABSTRACT FROM AUTHOR]

We review three broad categories of risk assessment methodology used for cartilaginous fish: productivity-susceptibility analysis (PSA), demographic methods, and quantitative stock assessments. PSA is generally a semi-quantitative approach useful as an exploratory or triage tool that can be used to prioritize research, group species with similar vulnerability or risk, and provide qualitative management advice. Demographic methods are typically used in the conservation arena and provide quantitative population metrics that are used to quantify extinction risk and identify vulnerable life stages. Stock assessments provide quantitative estimates of population status and the associated risk of exceeding biological reference points, such as maximum sustainable yield. We then describe six types of uncertainty (process, observation, model, estimation, implementation, and institutional) that affect the risk assessment process, identify which of the three risk assessment methods can accommodate each type of uncertainty, and provide examples mostly for sharks drawn from our experience in the United States. We also review the spectrum of stock assessment methods used mainly for sharks in the United States, and present a case study where multiple methods were applied to the same species (dusky shark, Carcharinus obscurus) to illustrate differing degrees of model complexity and type of uncertainty considered. Finally,we address the common and problematic case of data-poor by catch species. Our main recommendation for future work is to use Management Strategy Evaluation or similar simulation approaches to explore the effect of different sources of uncertainty, identify the most critical data to satisfy predetermined management objectives, and develop harvest control rules for cartilaginous fish. We also propose to assess the performance of data-poor and -rich methods through stepwise model construction. [ABSTRACT FROM AUTHOR]

Elasmobranch populations are declining worldwide, calling for urgent assessment of fishery exploitation and application of effective conservation strategies. Here, we applied a novel approach, integrating long-term time-series of landings (1945–2012) and extensive surveys at the fish market of Chioggia, Italy, home of the major fishing fleet of the northern Adriatic Sea, to evaluate the status of elasmobranch populations and fisheries in the one of the most fished Mediterranean basins. The time-series highlight a dramatic decline in elasmobranch landings, particularly for skates and catsharks (Scyliorhinus spp.), whose current catch rates are 2.4 and 10.6% of the average 1940s levels, respectively. These data likely reflect similar large reductions in abundance, as indicated by the analysis of catch-per unit-effort time-series. The biomass of landed skates and catsharks showed regular fluctuations that disappeared after the collapse of the landings. Elasmobranch market composition, assessed through the sampling of 11 900 specimens from 2006 to 2013, included 14 species, but was dominated by just two: Mustelus mustelus and M. punctulatus, which represented more than 60% of the catch. The proportion of sexually immature individuals was generally very high, up to 83% of landed females and 71% of landed males, depending on the species. Although some correlations were detected between landings and local hydrography or climatic indices, the analyses of landings and surveys at the fish market identified fishery exploitation as the main driver of the striking, long-term elasmobranch decline in the northern Adriatic Sea, calling for urgent management actions to improve the conservation status of these fish. [ABSTRACT FROM PUBLISHER]

Sharks and other cartilaginous fish are the phylogenetically oldest living organisms that rely on antibodies as part of their adaptive immune system. They produce the immunoglobulin new antigen receptor (IgNAR), a homodimeric heavy chain-only antibody, as a major part of their humoral adaptive immune response. Here, we report the atomic resolution structure of the IgNAR constant domains and a structural model of this heavy chain-only antibody. We find that despite low sequence conservation, the basic Ig fold of modern antibodies is already present in the evolutionary ancient shark IgNAR domains, highlighting key structural determinants of the ubiquitous Ig fold. In contrast, structural differences between human and shark antibody domains explain the high stability of several IgNAR domains and allowed us to engineer human antibodies for increased stability and secretion efficiency. We identified two constant domains, C1 and C3, that act as dimerization modules within IgNAR. Together with the individual domain structures and small-angle X-ray scattering, this allowed us to develop a structural model of the complete IgNAR molecule. Its constant region exhibits an elongated shape with flexibility and a characteristic kink in the middle. Despite the lack of a canonical hinge region, the variable domains are spaced appropriately wide for binding to multiple antigens. Thus, the shark IgNAR domains already display the well-known Ig fold, but apart from that, this heavy chain-only antibody employs unique ways for dimerization and positioning of functional modules. [ABSTRACT FROM AUTHOR]

Elasmobranchs are an important catch component in Tunisian artisanal fisheries. Generally, species-specific information is largely unavailable for artisanal fisheries; an increase in knowledge thereof is essential to ensure proper management of these species. The study analyzed the gillnet fishery elasmobranch catches in the Gulf of Gabès, whereby 45 fishing trips were conducted from April to June 2007 and 2008 for the capture of a total of six species: three Rajiformes and three Carchariniformes. Rhinobatos cemiculus was the most important species (52%; 4.588 ind km−2 net per day). Among shark species, Mustelus mustelus was the most important (66.8%; 2.21 ind km−2 net per day). Discards represented 6.87% of total catch in weight and 14.28% in number of specimens caught. Size composition of captures varied by species, but usually mature, mainly gravid females were abundant. Further investigations are needed to obtain more information on such fragile species for the development of protective measures. [ABSTRACT FROM AUTHOR]

A fossil-rich deposit occurring within Eocene strata is exposed along a roughly 600 meter-long section of the Conecuh River (at low water level) near the Point "A" Dam, north of River Falls in Covington County, Alabama. The deposit consists of bluish-green unconsolidated, poorly sorted, glauconitic quartz sand, and it contains abundant teeth and bones of elasmobranch, osteichthyan, and reptile taxa. The fossiliferous deposit is believed to have accumulated in a low energy coastal environment related to a third-order transgressive cycle. We propose that the disconformable contact between the fossiliferous deposit and an underlying burrowed siltstone is a sequence boundary, and that this disconformity represents the contact between the Tallahatta Formation and overlying Lisbon Formation. The fossiliferous deposit therefore constitutes the base of the Lisbon Formation. [ABSTRACT FROM AUTHOR]

AGr-43 is a fossil site located within a stream in central Greene County, Alabama that is bounded by the Black Warrior River to the east and the Tombigbee River to the west. The stream bed consists of fossil-rich gravel that contains large quantities of Cretaceous elasmobranch and bony fish remains, reptile and invertebrate remains, as well as carbonate and siliciclastic lithic fragments. Much of this material likely originates from the Tombigbee Sand Member of the Eutaw Formation (late Santonian to early Campanian), but some could be derived from the overlying Mooreville Chalk (late Santonian to early Campanian). Stream gravels were collected in bulk and later screened, picked, and sorted in the lab. Thus far, 28 Cretaceous fish taxa have been identified from these gravels, 22 of which are elasmobranchs and the remaining six are osteichthyans. Eleven of the specimens we discuss represent new published records for Alabama. These taxa include: Archaeolamna kopingensis, Anomoeodus barberi, Borodinopristis cf ackermani., Carcharias sp., Ischyrhiza aff. avonicola, Lonchidion sp., Meristodonoides sp., Micropycnodon sp.?, "Pseudohypolophus" ellipsis, Squalicorax aff. yangaensis, and Texatrygon sp. Furthermore, the identification of Chiloscyllium sp. and Ischyrhiza aff. mira represent the first of these taxa reported from the Tombigbee Sand of Alabama. The identification of these 28 taxa from site AGr-43 aids in our understanding of Late Cretaceous paleobiodiversity, biostratigraphy, and paleobiogeography within the Mississippi Embayment and Western Interior Seaway. [ABSTRACT FROM AUTHOR]

Dell'Apa, A., Kimmel, D. G., and Clò, S. 2012. Trends of fish and elasmobranch landings in Italy: associated management implications. – ICES Journal of Marine Science, 69: 1045–1052.Elasmobranchs are extremely vulnerable to overexploitation, owing to their specific biology and life-history characteristics. However, European-managed shark fisheries have historically received less attention than fisheries targeting more commercially important fish species. We analysed and compared the national data of elasmobranch and fish landings in Italy between 1959 and 2004 to examine changes in fishery interest and the exploitation of elasmobranchs over time. Rays (Raja spp.) and smooth-hounds (Mustelus spp.) are the only elasmobranch categories present in the data, but also other similar species could have been mistakenly counted within these groups. Elasmobranch landings were steady until the beginning of the 1970s, peaked in the 1990s, then sharply declined. The mean annual landing for elasmobranchs between 1997 and 2004 decreased 77% compared with the previous years (1959–1982). This decrease may be attributed to overharvesting that occurred during the 1980s and 1990s in Italian seas. This was likely a direct consequence of the 41/82-law, which was developed to manage fish and not elasmobranchs. A direct effect of the 41/82-law was the establishment of an unreported and unregulated elasmobranch fishery since 1983 that lasted almost 10 years. We suggest that the conservation status of elasmobranch species in the Mediterranean and Black Seas be reconsidered. [ABSTRACT FROM PUBLISHER]

The expansion of commercial aquaculture production has raised awareness of issues relating to the welfare of aquatic animals. The 'Five Freedoms' approach to animal welfare was originally devised for farmed terrestrial animals, and has been applied in some countries to aquatic animals reared in aquaculture due to several commonalities inherent within food production systems. There are now moves towards assessing and addressing aquatic animal welfare issues that may arise in wild capture fisheries. However, all 'five freedoms' are regularly contradicted in the natural environment, meaning this concept is inappropriate when considering the welfare of aquatic animals in their natural environments. The feelings-based approach to welfare relies on a suffering centered view that, when applied to the natural aquatic environment, requires use of value judgements, cannot encompass scientific uncertainty regarding awareness in fish, elasmobranchs and invertebrates (despite their unquestioned welfare needs), and cannot resolve the welfare conundrums posed by predator-prey interactions or anthropocentrically mediated environmental degradation. For these reasons, the feelings-based approach to welfare is inadequate, inappropriate and must be rejected if applied to aquatic animals in wild capture fisheries, because it demonstrably ignores empirical evidence and several realities apparent within the natural aquatic environment. Furthermore, application of the feelings-based approach is counterproductive as it can alienate key fisheries stakeholders, many of whom are working to address environmental issues of critical importance to the welfare, management and conservation of aquatic animal populations in their natural environment. In contrast, the function-based and nature-based approaches for defining animal welfare appear appropriate for application to the broad range of welfare issues (including emerging environmental issues such as endocrine disruption) that affect aquatic animals in their natural environment, without the need to selectively ignore groups such as elasmobranchs and invertebrates. We consider that the welfare needs of aquatic animals are inextricably entwined with the need for conservation of their populations, communities and their environment, an approach that is entirely consistent with the concept of ecosystem-based management. [ABSTRACT FROM AUTHOR]

A rapid semi-quantitative ecological risk assessment method (productivity and susceptibility analysis) indicated that, despite its low biological productivity, the Port Jackson shark Heterodontus portusjacksoni is at low risk to all fishing methods in far-eastern Victoria, Australia, under the present fishing practices, because of its low catch susceptibility. The risk to this population, however, would increase if the shark gillnet fishery operating in the region were to retain the species as a by-product. Demographic analysis indicated that the species has medium intrinsic population growth rate and potential rebound in comparison with other chondrichthyan species, juveniles have higher elasticity than mature females and both juvenile and mature females have higher elasticities than hatchlings. Because of its low biological productivity and moderate resilience to the effects of fishing, cautious management measures will be necessary to ensure the sustainable use of H. portusjacksoni if its marketing increases in the future. Information on the dynamics of a population that is valuable to provide management advice can be obtained through demographic methods, but rapid assessment methods can also provide complementary information on the effects of fishing by considering the catch susceptibility of the population to each fishing method. [ABSTRACT FROM AUTHOR]

Ecology Letters (2010) 13: 1055–1071 Whereas many land predators disappeared before their ecological roles were studied, the decline of marine apex predators is still unfolding. Large sharks in particular have experienced rapid declines over the last decades. In this study, we review the documented changes in exploited elasmobranch communities in coastal, demersal, and pelagic habitats, and synthesize the effects of sharks on their prey and wider communities. We show that the high natural diversity and abundance of sharks is vulnerable to even light fishing pressure. The decline of large predatory sharks reduces natural mortality in a range of prey, contributing to changes in abundance, distribution, and behaviour of small elasmobranchs, marine mammals, and sea turtles that have few other predators. Through direct predation and behavioural modifications, top-down effects of sharks have led to cascading changes in some coastal ecosystems. In demersal and pelagic communities, there is increasing evidence of mesopredator release, but cascading effects are more hypothetical. Here, fishing pressure on mesopredators may mask or even reverse some ecosystem effects. In conclusion, large sharks can exert strong top-down forces with the potential to shape marine communities over large spatial and temporal scales. Yet more empirical evidence is needed to test the generality of these effects throughout the ocean. [ABSTRACT FROM AUTHOR]

The composition of lipids and fatty acids was determined for the livers, muscle, pancreas, kidney and stomach fluids of deepwater chondrichthyan species (including 11 squaliformes, 3 chimaeriformes, 1 hexanchiforme and 3 carcharhiniformes) caught as bycatch from continental waters off south-eastern Australia. The lipid class, fatty acid and fatty alcohol composition differed markedly in each tissue and in each species. The lipid and fatty acid composition of large, lipid-rich (38–70% wet weight, ww) livers demonstrated the multifunctional role of this organ in: lipid distribution, storage and biosynthesis, and buoyancy regulation. In the liver, the importance of certain lipids (including squalene, diacylglyceryl ethers, triacylglycerols and to a lesser extent wax esters) as mediators of buoyancy varied according to lifestyle and habitat. Less variability was observed in the muscle profiles, characterized by low lipid content (<1.0% ww) and high relative levels of polar lipids (>70%). The lipid and fatty acid profiles of the kidney and pancreas showed the highest intraspecific variability, suggesting these organs also have complex roles in lipid storage and metabolism. Overall intra- and interspecific differences in the tissue fatty acid profiles could be related to differences in a number of factors including phylogeny, habitat (depth), buoyancy regulation and diet and presumably also reflect different ecological roles. The lipid and fatty acid profiles are the first published for Rhinochimaera pacifica, Chimaera lignaria and Figaro boardmani and the first to demonstrate interspecific variation in lipid profiles of various tissues of deepwater chondrichthyans. The application of multivariate analysis to lipid class and fatty acid tissue profiles in chondrichthyans inferred dietary differences and metabolic preferences between species and habitats. These results have important implications for the future use of fatty acids as dietary tracers in chondrichthyan research. [ABSTRACT FROM AUTHOR]

The status of chondrichthyan (sharks, batoids and chimaeras) conservation in the Indo-Australasian region is examined, and issues relevant to the conservation of this fauna at the subregional level [Australia, Indonesia (excluding West Papua), New Guinea (West Papua and Papua New Guinea), New Caledonia and New Zealand] are discussed. According to the 2009 IUCN Red List of Threatened Species, c. 21% of Indo-Australasian chondrichthyans are classified as threatened (critically endangered, endangered and vulnerable) and c. 40% are of conservation concern (threatened and near threatened). The proportion of threatened species is highest in New Guinea ( c. 39%) and Indonesia ( c. 35%) and least in New Zealand ( c. 11%). In New Guinea, three quarters of the species are of conservation concern; in Indonesia, nearly two thirds are of conservation concern. Within the region, the proportion of threatened batoids ( c. 29%) is higher than threatened sharks ( c. 17%), while there are no threatened chimaeras. Conservation status is discussed at the order (for sharks), suborder (for batoids) and family level. Issues relating to the conservation status of chondrichthyans vary greatly between each subregion, but they mostly relate to targeted or incidental capture in fisheries. A handful of sharks and batoids are protected within Australian waters, while one species is protected in New Zealand. Both Australia and New Zealand have developed National Plans of Action for the Conservation and Management of Sharks (NPOA-Sharks), but these are lacking elsewhere. Development and implementation of NPOA-Sharks are a priority in order to drive the conservation of the regional fauna. Sustainable fisheries management (including by-catch), confronting the challenge of illegal, unreported and unregulated fishing, species protection where appropriate and marine protected areas (MPA) are all likely to prove vital in ensuring the long-term conservation of Indo-Australasian sharks, batoids and chimaeras. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the relationship of recreational fishing in the conservation of elasmobranch, such as sharks and rays, in the Great Barrier Reef Marine Park in Queensland. The target population of study are the recreational fishers in Townsville region of North Queensland ages 15 years or above who were asked to provide data about their fishing trips. It shows that catching elasmobranch is less valued by recreational fishers because of its lower consumption quality.

For more than a century, two major zoogeographic provinces have been proposed for the southwestern Atlantic: a warm water Argentinean Province from Rio de Janeiro (23°S, Brazil) to Valdés Peninsula (42°S, Argentina), and a cold water Magellanic Province from Valdés Peninsula to Cape Horn. This zoogeographic scheme has been recognized so far using data covering only parts of the whole geographic area. Here, we test the validity of this scheme by analyzing the distribution of sharks, skates, rays and chimaeras, using data from research cruises covering the entire area. We used cluster, similarity and dissimilarity analyses to identify species assemblages, and canonical correspondence analysis to identify the main environmental variables affecting the composition of the assemblages. The distribution of chondrichthyan assemblages strongly supports the current zoogeographic scheme and identifies a previously unknown and distinctive deep water zoogeographic unit off southern Brazil. Both, the Argentinean and Magellanic Provinces had extensive internal structure, with four and three subareas identified in each of them, respectively. These subareas correspond, with slight differences, to previously proposed zoogeographical districts within the Argentinean Province and confirm ecological differences within the Magellanic Province. Species composition had the highest correlation with depth and bottom water temperature. Since the distribution of anthropogenic disturbances in the region is uneven, different assemblages can be subjected to different impacts. Our results provide an objective basis to establish priority areas for the conservation of chondrichthyans in the southwestern Atlantic. [ABSTRACT FROM AUTHOR]

Eight species of pandarid copepods are redescribed based on specimens recovered from six species of Japanese elasmobranchs. These are Pandarus cranchii Leach, 1819, P. smithii Rathbun, 1886, Gangliopus pyriformis Gerstaecker, 1854, Pseudopandarus gracilis Kirtisinghe, 1950, Dinemoura latifolia (Steenstrup & Lütken, 1861), Echthrogaleus coleoptratus (Guérin-Méneville, 1837), E. denticulatus Smith, 1874, and Nesippus orientalis Heller, 1868. In P. cranchii, both sexes of copepodid IV and V are described, one of them retains the frontal filament. The postnaupliar juveniles preceding the adult are referred to here as copepodid stages instead of chalimus. The presence of the postantennal process was verified in all species here dealt with, though it is replaced by an additional adhesion pad in D. latifolia. The depression, seemingly acting as the sucker, was found in N. orientalis on the female leg 3 basis. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tetraphyllidean cestodes are cosmopolitan, remarkably host specific, and form the most speciose and diverse group of helminths infecting elasmobranchs (sharks, skates and rays). They show substantial interspecific variation in a variety of morphological traits, including body size. Tetraphyllideans represent therefore, an ideal group in which to examine the relationship between parasite body size and abundance. The individual and combined effects of host size, environmental temperature, host habitat, host environment, host physiology, and host type (all likely correlates of parasite body size) on parasite length were assessed using general linear model analyses using data from 515 tetraphyllidean cestode species (182 species were included in analyses). The relationships between tetraphyllidean cestode length and intensity and abundance of infection were assessed using simple linear regression analyses. Due to the contrasting morphologies between shark and batoid hosts, and contrasting physiologies between sharks of the Lamnidae family and other sharks, analyses were repeated in different subsets based on host morphology and physiologies (“sharks” vs. batoids) to determine the influence of these variables on adult tetraphyllidean tapeworm body size. Results presented herein indicate that host body size, environmental temperature and host habitat are relatively important variables in models explaining interspecific variations in tetraphyllidean tapeworm length. In addition, a negative relationship between tetraphyllidean body size and intensity of infection was apparent. These results suggest that space constraints and ambient temperature, via their effects on metabolism and growth, determine adult tetraphyllidean cestode size. Consequently, a trade-off between size and numbers is possibly imposed by external forces influencing host size, hence limiting physical space or other resources available to the parasites. [ABSTRACT FROM AUTHOR]

The present study provides a check list of elasmobranchs from the Paraná State coast, southern Brazil. Information from fish collections, literature data, field surveys and personal communications were included. Results indicated that 83 species from seven orders and 28 families were recorded. According to the results 51 species belonging to six orders and 17 families of sharks; and 32 species belonging to one order and eleven families of rays occur in this region. The most species-rich families were Carcharhinidae (14 species) and Arhynchobatidae (eight species). [ABSTRACT FROM AUTHOR]

The fisheries management system in the northeast Atlantic is complicated. It was not designed with management or conservation of elasmobranchs in mind. Gradually, however, the system has taken elasmobranchs into account. Managers have asked science to provide advice, and in some cases management actions have followed. The purpose of this short review is to explain the system of assessment and advice, especially how it relates to sharks, skates and rays. Emphasis is on the legal framework, however, soft law and the role of the conservation movement are also discussed. [ABSTRACT FROM AUTHOR]

The visual abilities of sharks show substantial interspecific variability. In addition, sharks may change their habitat and feeding strategy throughout life. As the eyes of sharks continue to grow throughout the animal's lifetime, ontogenetic variability in visual ability may also occur. The topographic analysis of the photoreceptor and ganglion cell distributions can identify visual specializations and assess changes in visual abilities that may occur concurrently with eye growth. This study examines an ontogenetic series of whole-mounted retinas in two elasmobranch species, the sandbar shark, Carcharhinus plumbeus, and the shortspine spurdog, Squalus mitsukurii, to identify regional specializations mediating zones for improved spatial resolution. The study examines retinal morphology and presents data on summation ratios between photoreceptor and ganglion cell layers, anatomically determined peak spatial resolving power, and the angular extent of the visual field. Peak densities of photoreceptors and ganglion cells occur in similar retinal locations. The topographic distribution of neurons in the ganglion cell layer does not differ substantially with eye growth. However, predicted peak spatial resolution increases with eye growth from 4.3 to 8.9 cycles/deg in C. plumbeus and from 5.7 to 7.2 cycles/deg in S. mitsukurii. The topographic distribution of different-sized ganglion cells is also mapped in C. plumbeus, and a population of large ganglion cells (soma area 120-350 μm²) form a narrow horizontal streak across the retinal meridian, while the spatial distribution of ordinary-sized ganglion cells (soma area 30-120 μm²) forms an area in the central retina. Species-specific retinal specializations highlight differences in visually mediated behaviors and foraging strategies between C. plumbeus and S. mitsukurii. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Shark teeth and scales from the Gneudna Formation type section, Carnarvon Basin are rare, but they represent a diverse fauna as well as being the first Frasnian chondrichthyan remains found in Western Australia. In contrast numerous shark teeth and scales have been obtained from coeval sections in the Canning Basin. Teeth referred to as Phoebodus bifurcatus, Phoebodus fastigatus, Phoebodus cf. fastigatus, Phoebodus latus, Phoebodus sp. C and Protacrodus sp. 1 are described from two Canning Basin localities: Horse Spring Range and McIntyre Knolls. The phoebodont species described here have a global distribution and can, therefore, be placed within the standard Frasnian phoebodont zonation. The shark remains from the Gneudna Formation type section include one new genus Emerikodus ektrapelus gen. et sp. nov., described along with Helodontidae indet and Elasmobranchii gen. et sp. indet. It is proposed that the faunal differences observed between the localities are a result of environmental differences. In addition to shark remains, scales from the thelodont Australolepis seddoni were also recovered from each locality. The well-dated Zone 6–10 conodont faunas at Horse Spring constrain the range of A. seddoni with which they occur, and importantly indicate that the Gneudna Formation type section is wholly Frasnian. [ABSTRACT FROM AUTHOR]

Ontogenetic diet shifts are a widespread phenomenon among vertebrates, although their relationships with life history traits are poorly known. We analyzed the relative importance of body size, age and maturity stage as determinants of the diet of a marine top predator, the copper shark, Carcharhinus brachyurus, by examining stomach contents using a multiple-hypothesis modeling approach. Copper sharks shifted their diet as size and age increased and as they became sexually mature, incorporated larger prey as they grew, and had a discrete shift in diet with body size, with only individuals larger than ≈200 cm total length able to prey on chondrichthyans. Body size was the most important trait explaining the consumption of chondrichthyans, while age determined the consumption of pelagic teleosts. Pelagic teleosts were consumed mostly by medium-aged sharks, a result, probably, of a risk-reducing feeding strategy at young ages coupled with either a senescence-related decline in performance or a change in sensory capabilities as sharks age. Copper sharks of all sizes were able to cut prey in pieces, implying that gape limitation (i.e., the impossibility of eating prey larger than a predator’s mouth) did not play a role in producing the diet shift. Our results suggest that, contrary to the current practice of setting minimum but not maximum size limits in catches, any plan to conserve or restore the ecological function of sharks, through their predatory control of large prey, should aim to maintain the largest individuals. [ABSTRACT FROM AUTHOR]

A quantitative frequency-domain model of induction-based magnetoreception is presented for elasmobranch fishes. We show that orientation with respect to the geomagnetic field can be determined by synchronous detection of electrosensory signals at harmonics of the vestibular frequency. The sensitivity required for this compass-sense mechanism is shown to be less than that known frombehavioral experiments. Recent attached-magnet experiments have called into doubt the induction-based mechanism for magnetoreception. We show that the use of attached magnets would interfere with an induction-based mechanism unless relative movement between the electrosensory system and the attached magnet is less than 100 μm. This suggests that further experiments may be required to eliminate induction as a basis for magnetoreception. [ABSTRACT FROM AUTHOR]

Age, growth and sexual maturity of the fan ray Platyrhina sinensis in Ariake Bay, Japan were determined from specimens collected from May 2002 to September 2006. Age determination was conducted by vertebral centrum analysis using soft X-radiography. Annual band pair deposition was determined by marginal increment and edge analyses. The von Bertalanffy growth model best described the overall pattern of growth for both males and females (males L ∝ = 455.2, k = 0.56, t0 = −1.09; females L ∝ = 555.8, k = 0.28, t0 = −1.77; L ∝ is the theoretical asymptotic total length in mm, k is the growth rate coefficient and t0 is the theoretical time at zero length). Parameter estimates suggest that females attain a larger asymptotic total length and grow more slowly than males. The observed maximum ages were 5 years for males and 12 years for females. Age at 50% sexual maturity was 2.1 years for males and 2.9 years for females. The results indicate that this species is relatively fast-growing, short-lived and early maturing compared with many batoid species. [ABSTRACT FROM AUTHOR]