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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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Clearnose skates, Raja eglanteria, are a common species of skate found seasonally along the Atlantic coast of North America from Cape Cod to mid-Florida and in the Gulf of Mexico from mid-Florida to eastern Texas. Clearnose skates inhabit the west central coast of Florida during winter months, when Gulf temperatures are conducive to mating and egg-laying (approximately 16°C–22°C). Specimens collected during this time will breed in captivity and, if maintained at 20°C, mated females will store sperm and continue to lay fertile eggs for up to six months. With fertile eggs available from day of laying until hatching, the first complete description of batoid elasmobranch embryonic development with a timetable has been established and is presented here. If eggs are maintained at 20°C, appearance and progression of embryonic events proceed over a reproducible timeline. The timeline has been divided into discrete time periods into which developmental events have been grouped. These include cleavage and expansion of the blastodisc (day 1–day 4), embryonic axis and neural tube formation (day 4–day 7), pharyngeal pouches and gill filament development (day 10–day 28), expansion of fins and transition from external filaments to internal gills (week 4–week 7), and epidermal pigmentation and yolk absorption (week 8–week 12). Fully formed offspring hatch after an incubation period of approximately 12 weeks (85 ± 6 days). To examine possible mechanisms of transport and storage of sperm in the reproductive tract of females following copulation, experiments resulting in the first artificial insemination for any elasmobranch fish are described. These experiments provide evidence for functional roles of the alkaline gland, whose secretions stimulate sperm motility and may enhance migration of sperm to the oviducal glands, and the clasper gland, whose secretions may provide nutrition during storage of viable sperm in the oviducal gland. [ABSTRACT FROM AUTHOR]

It is often assumed that the von Bertalanffy growth model (VBGM) is appropriate to describe growth in length-at-age of elasmobranchs. However, a review of the literature suggests that a two-phase growth model could better describe growth in elasmobranchs. We compare the two-phase growth model (TPGM) with the VBGM for 18 data sets of elasmobranch species, by fitting the models to 36 age-length-at-age data pairs available. The Akaike Information Criteria (AIC) and the difference in AIC between both models revealed that in 23 cases the probability that the TPGM was true ≥50%. The VBGM tends to estimate larger L ∞ values than the two-phase growth model, while the k parameter tends to be underestimated. The growth rate in length-at-age appears tends to decrease near the age at first maturity in several species of elasmobranch. The importance of the TPGM lies in that it may better describe this aspect of the life history of many elasmobranchs. In this context, we conclude that the TPGM should be used along with other growth models in order to precisely estimate elasmobranch life history parameters. [ABSTRACT FROM AUTHOR]

The shortfin mako, Isurus oxyrinchus, is caught in the eastern North Atlantic as a regular bycatch of the surface-drift longline fishery, mainly directed towards swordfish, Xiphias gladius. Stomachs of 112 shortfin mako sharks, ranging in size from 64 cm to 290 cm fork length, showed teleosts to be the principal component of the diet, occurring in 87% of the stomachs and accounting for over 90% of the contents by weight. Crustaceans and cephalopods were also relatively important in this species’ diet, whereas other elasmobranchs were only present in lower percentages. Meal overlap was observed in half of the sampled sharks. No clear trend of prey size selectivity was found, despite smaller individuals seeming incapable of pursuing larger and faster prey. The retention of small prey was also observed in the diet of all sizes of shark. Seasonality in food habits was in accordance with the current availability of food items. The observed vacuity index of 12% is comparable to foraging ecology studies using gillnetting and appears not to be influenced by baited longline gear. Morphological relationships of the digestive system might add important information to the foraging ecology studies and to ecosystem modelling. [ABSTRACT FROM AUTHOR]

Effects of environmental factors on frequency and success rate of 2,546 natural predatory attacks by white sharks, Carcharodon carcharias, on Cape fur seals, Arctocephalus pusillus pusillus, were studied over an 8-year period at Seal Island, South Africa. Attacks occurred primarily during winter months (June–August). Attack frequency increased significantly during northerly winds, during high tides, and within 400 m of the island, but predatory success rate decreased with proximity to the island. Attacks occurred over a depth range of 5–31 m, with significantly more occurring at depths of 26–30 m. Attack frequency and success rate increased significantly at low light levels. These results are compared with published effects of environmental factors on white shark predation frequency at the Farallon Islands, California, and discussed in terms of the Predation Cycle. Suggestions for future work at this site are offered. [ABSTRACT FROM AUTHOR]

This study examined the osmoregulatory status of the euryhaline elasmobranchCarcharhinus leucasacclimated to freshwater (FW) and seawater (SW). JuvenileC. leucascaptured in FW (3 mOsm l-1 kg-1) were acclimated to SW (980-1,000 mOsm l-1 kg-1) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l-1 kg-1. In SW, bull sharks had significantly higher plasma osmolarities (940 mOsm l-1 kg-1) than FW-acclimated animals and were slightly hypo-osmotic to the environment. Plasma Na+, Cl-, K+, Mg2+, Ca2+, urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and analysed for maximal Na+/K+-ATPase activity. Na+/K+-ATPase activity in the gills and intestine was less than 1 mmol Pi mg-1 protein h-1 and there was no difference in activity between FW- and SW-acclimated animals. In contrast Na+/K+-ATPase activity in the rectal gland and kidney were significantly higher than gill and intestine and showed significant differences between the FW- and SW-acclimated groups. In FW and SW, rectal gland Na+/K+-ATPase activity was 5.6±0.8 and 9.2±0.6 mmol Pi mg-1 protein h-1, respectively. Na+/K+-ATPase activity in the kidney of FW and SW acclimated animals was 8.4±1.1 and 3.3±1.1 Pi mg-1 protein h-1, respectively. Thus juvenile bull sharks have the osmoregulatory plasticity to acclimate to SW; their preference for the upper reaches of rivers where salinity is low is therefore likely to be for predator avoidance and/or increased food abundance rather than because of a physiological constraint. [ABSTRACT FROM AUTHOR]

The present study investigated the thermal stability and denaturation rate of myoglobin (Mb) from migratory, demersal, aquaculture and elasmobranch fish species using thermal analysis and dynamic analysis of Mb denaturation. The concentration of Mb was 1.86–2.80 mg/g muscle in the migratory fish, and the tilapia had the lowest Mb concentration of 0.94 mg/g muscle. By analyzing the phase transition temperature (Tm) and denaturation rate of Mb, dolphinfish and horse mackerel Mb showed lower Tm at 46.4 and 51.8°C, respectively. The main endothermic peak was around 71.8°C for spotted shark Mb. Although the Mb denaturation behaved as biphasic first-order reaction for all the Mb examined, spotted shark Mb showed the highest thermal stability and was followed by chub mackerel and tilapia Mb. The horse mackerel Mb showed the lowest thermal stability. [ABSTRACT FROM AUTHOR]

We determined the hearing sensitivity of the little skate, Raja erinacea using two methods: Behavioral conditioning and the auditory brainstem response (ABR). This marks the first time that the hearing in any member of the Rajiformes has been examined and the first time that the ABR method has been used with an elasmobranch. We obtained audiograms of R. erinacea using each method and were found to be statistically similar. The best hearing sensitivity for R. erinacea was between 100 and 300 Hz. We compared the audiograms to audiograms obtained from other species of elasmobranchs. This analysis showed that R. erinacea, a bottom-dwelling elasmobranch, has less sensitive hearing than the lemon shark, Negaprion brevirostris, and the bull shark, Carcharhinus leucas, a free-swimming, raptorial elasmobranch. However, R. erinacea showed sensitivity comparable to that of the horn shark, Heterodontus francisi, another bottom-dwelling elasmobranch; both species feed primarily on benthic prey. These findings are in agreement with Corwin's hypothesis (1978) that hearing sensitivity is correlated with feeding behavior. An examination of the macula neglecta of R. erinacea found a total count of 10 000 hair cells, which is within the range of other bottom-dwelling elasmobranchs. [ABSTRACT FROM AUTHOR]

A report on the auditory capabilities and their associated functions of elasmobranch fishes along with a brief review of the physics of underwater sound as it relates to hearing by fishes is provided. The inner ears of elasmobranchs possess structures that are no different from other fishes, except for an enlarged macula neglecta, which is unique among fishes. Hearing abilities among sharks (the only elasmobranchs examined) have demonstrated highest sensitivity to low frequency sound (40 Hz to approximately 800 Hz), which is sensed solely through the particle-motion component of an acoustical field. Free-ranging sharks are attracted to sounds possessing specific characteristics: irregularly pulsed, broad-band (most attractive frequencies: below 80 Hz), and transmitted without a sudden increase in intensity. Such sounds are reminiscent of those produced by struggling prey. A sound, even an attractive one, can also result in immediate withdrawal by sharks from a source, if its intensity suddenly increases 20 dB [10 times] or more above a previous transmission. Present evidence also shows that the lateral line system does not respond to normal acoustical stimuli. Morphological and physiological evidence suggest that the maculae neglecta possess acoustical relevance and may explain directionality of response despite physical principles that provide still other hypotheses for acoustical directionality. Brain centers controlling acoustical response, particularly among sharks, must be explored in the near future with careful consideration of the habits of subjects based on indications of species-differences regarding the importance of acoustical stimuli to their activities. Numerous facts and ideas about the acoustical biology of elasmobranch fishes make certain that future research will be most rewarding. [ABSTRACT FROM AUTHOR]

Physiological telemetry is a powerful tool in studying the thermal biology and energetics of elasmobranchs in the laboratory and field. Controlled laboratory studies have increased our understanding of the physiology and behavior of many elasmobranchs, but have focused primarily on small, slow moving species. Extrapolating results from these laboratory studies to free-swimming animals in the field or to other unstudied species may be problematic, due to laboratory constraints or species specific differences. Some elasmobranchs are too large or logistically difficult to maintain in captivity, making them extremely difficult to study in the laboratory, and thus can only be studied in the field. Physiological telemetry offers a ‘bridge’ between the laboratory and the field providing an opportunity to elucidate similarities and differences. Previous studies have coupled a variety of sensors with ultrasonic transmitters to relay information on epaxial muscle and stomach temperatures of free-swimming lamnid sharks. Even though these studies indicate lamnids exhibit elevated body temperatures, the degree to which these sharks may control body temperature is still not fully understood. Telemetry of heart rate, swimming speed, muscle contraction rate, and tail beat frequency has been used to estimate energy consumption of free-swimming elasmobranchs with varying success. Based on recent advances in technology, several hypotheses regarding thermoregulation, cardiac output, and obligate ram ventilation are discussed. Although many telemetry studies have been restricted by logistical difficulties in conducting long-term tracks, recent developments such as acoustic modems, underwater listening stations and satellite telemetry may significantly increase the amount and types of physiological data that can be collected. These improvements in technology and captive animal husbandry techniques will help to ‘bridge the gap’ between the laboratory and the field. [ABSTRACT FROM AUTHOR]

The organization of the vertebrate cerebellum has been thoroughly studied over the past century, but the function of this structure remains poorly understood. In elasmobranch fishes, the cerebellum displays tremendous variation in size and development although the basic and conservative nature of cerebellar circuitry as seen in other vertebrate taxa is largely retained. Large and morphologically complex cerebelli have evolved independently in both sharks and batoids, and the relative development of this structure in both taxa parallels those of birds and mammals. There are relatively few studies of the physiological role of the cerebellum in generating or shaping behaviors, however, and a convincing explanation of cerebellar hypertrophy in elasmobranchs is lacking. The purpose of this article is to review the current understanding of the structure of the cerebellum in elasmobranch fishes, the physiological responses of cerebellar neurons and the possible role of the cerebellum in behavior. I will also provide a number of hypotheses for future research directions, based upon models that have been suggested by different investigators. These hypotheses include models of cerebellar function as a sensory coincidence detector, a dynamic state estimator and/or a direct modulator of motor programs. Hypotheses concerning the possible organization of cerebellar microcomplexes, the evolution of afferent and efferent cerebellar connections paralleling those observed in mammals and the role of the cerebellum in learning are also suggested. [ABSTRACT FROM AUTHOR]

Elasmobranch reproductive behavior has been inferred from freshly caught specimens, laboratory examinations of reproductive structures and function, or determined from direct observations of captive or free swimming wild animals. Several general behaviors have been described including seasonal sexual segregation, courtship and copulation. Courtship behavior was inferred for many species from the presence of scars and tooth cuts on the female's body, and noted in more detail from underwater observations. Copulation has been directly observed in captive settings for several species of elasmobranchs in large aquaria, and in the wild for three species of urolophids and for Triaenodon obesus and Ginglymostoma cirratum. A detailed ‘case history’ of nurse shark reproductive behavior is presented that may be used as a template for future work on shark reproductive behavior of other species. Our studies, using diver identifiable tags and in situ behavioral observations, provide unprecedented information on social structure and mating behavior in this species. Since 1993, 115 G. cirratum, 45 adults and 70 juveniles have been tagged in the Dry Tortugas, Florida. Observations show that adult males visit the study site every year with three males dominant. Individual adult females visit the study area to mate in alternate years. Polygyny and polyandry are common. Future research on reproductive behavior of elasmobranchs should address questions on male access to females, sexual selection and dominance hierarchies. [ABSTRACT FROM AUTHOR]

Commercial fisheries have dramatically impacted elasmobranch populations worldwide. With high capture and bycatch rates, the abundance of many species is rapidly declining and around a quarter of the world's sharks and rays are threatened with extinction. At a regional scale this negative trend has also been evidenced in the central Mediterranean Sea, where bottom-trawl fisheries have affected the biomass of certain rays (e.g. Raja clavata) and sharks (e.g. Mustelus spp.). Detailed knowledge of elasmobranch habitat requirements is essential for biodiversity conservation and fisheries management, but this is often hampered by a poor understanding of their spatial ecology. Habitat suitability models were used to investigate the habitat preference of nine elasmobranch species and their overall diversity (number of species) in relation to five environmental predictors (i.e. depth, sea surface temperature, surface salinity, slope and rugosity) in the central Mediterranean Sea. Results showed that depth, seafloor morphology and sea surface temperature were the main drivers for elasmobranch habitat suitability. Predictive distribution maps revealed different species-specific patterns of suitable habitat while high assemblage diversity was predicted in deeper offshore waters (400-800 m depth). This study helps to identify priority conservation areas and diversity hot-spots for rare and endangered elasmobranchs in the Mediterranean Sea. [ABSTRACT FROM AUTHOR]