Dual annual spawning races in Atlantic sturgeon

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus, Acipenseridae) populations in the United States were listed as either endangered or threatened under the Endangered Species Act in 2012. Because of the endangered/threatened status, a better understanding of Atlantic sturgeon life-history behavior and habitat use is important for effective management. It has been widely documented that Atlantic sturgeon reproduction occurs from late winter to early summer, varying clinally with latitude. However, recent data show Atlantic sturgeon also spawn later in the year. The group that spawns later in the year seems to be completely separate from the spring spawning run. Recognition of the later spawning season has drastically modified estimates of the population status of Atlantic sturgeon in Virginia. With the combination of new telemetry data and historical documentation we describe a dual spawning strategy that likely occurs in various degrees along most, if not all, of the Atlantic sturgeon's range. Using new data combined with historical sources, a new spawning strategy emerges which managers and researchers should note when determining the status of Atlantic sturgeon populations and implementing conservation measures.

Extinction risk and conservation of the world's sharks and rays

The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes-sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world's ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery. DOI: http://dx.doi.org/10.7554/eLife.00590.001.

Extinction risk and conservation of the world's sharks and rays

The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes—sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world’s ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery.

DOI:http://dx.doi.org/10.7554/eLife.00590.001

Ocean ecosystems are under pressure from overfishing, climate change, habitat destruction and pollution. These pressures have led to documented declines of some fishes in some places, such as those living in coral reefs and on the high seas. However, it is not clear whether these population declines are isolated one-off examples or, instead, if they are sufficiently widespread to risk the extinction of large numbers of species.

Most fishes have a skeleton that is made of bone, but sharks and rays have a skeleton that is made of cartilage. A total of 1,041 species has such a skeleton and they are collectively known as the Chondrichthyes. To find out how well these fish are faring, Dulvy et al. worked with more than 300 scientists around the world to assess the conservation status of all 1,041 species.

Based on this, Dulvy et al. estimate that one in four of these species are threatened with extinction, mainly as a result of overfishing. Moreover, just 389 species (37.4% of the total) are considered to be safe, which is the lowest fraction of safe species among all vertebrate groups studied to date.

The largest sharks and rays are in the most peril, especially those living in shallow waters that are accessible to fisheries. A particular problem is the ‘fin trade’: the fins of sharks and shark-like rays are a delicacy in some Asian countries, and more than half of the chondrichthyans that enter the fin trade are under threat. Whether targeted or caught by boats fishing for other species, sharks and rays are used to supply a market that is largely unmonitored and unregulated. Habitat degradation and loss also pose considerable threats, particularly for freshwater sharks and rays.

Dulvy et al. identified three main hotspots where the biodiversity of sharks and rays was particularly seriously threatened—the Indo-Pacific Biodiversity Triangle, Red Sea, and the Mediterranean Sea—and argue that national and international action is needed to protect them from overfishing.

DOI:http://dx.doi.org/10.7554/eLife.00590.002

Comparative metabolic rates of common western North Atlantic Ocean sciaenid fishes

The resting metabolic rates (R(R)) of western North Atlantic Ocean sciaenids, such as Atlantic croaker Micropogonias undulatus, spot Leiostomus xanthurus and kingfishes Menticirrhus spp., as well as the active metabolic rates (R(A)) of M. undulatus and L. xanthurus were investigated to facilitate inter and intraspecific comparisons of their energetic ecology. The R(R) of M. undulatus and L. xanthurus were typical for fishes with similar lifestyles. The R(R) of Menticirrhus spp. were elevated relative to those of M. undulatus and L. xanthurus, but below those of high-energy-demand species such as tunas Thunnus spp. and dolphinfish Coryphaena hippurus. Repeated-measures non-linear mixed-effects models were applied to account for within-individual autocorrelation and corrected for non-constant variance typical of noisy R(A) data sets. Repeated-measures models incorporating autoregressive first-order [AR(1)] and autoregressive moving average (ARMA) covariances provided significantly superior fits, more precise parameter estimates (i.e. reduced s.e.) and y-intercept estimates that more closely approximated measured R(R) for M. undulatus and L. xanthurus than standard least-squares regression procedures.

Regional management units for marine turtles: a novel framework for prioritizing conservation and research across multiple scales

Background

Resolving threats to widely distributed marine megafauna requires definition of the geographic distributions of both the threats as well as the population unit(s) of interest. In turn, because individual threats can operate on varying spatial scales, their impacts can affect different segments of a population of the same species. Therefore, integration of multiple tools and techniques — including site-based monitoring, genetic analyses, mark-recapture studies and telemetry — can facilitate robust definitions of population segments at multiple biological and spatial scales to address different management and research challenges.

Methodology/Principal Findings

To address these issues for marine turtles, we collated all available studies on marine turtle biogeography, including nesting sites, population abundances and trends, population genetics, and satellite telemetry. We georeferenced this information to generate separate layers for nesting sites, genetic stocks, and core distributions of population segments of all marine turtle species. We then spatially integrated this information from fine- to coarse-spatial scales to develop nested envelope models, or Regional Management Units (RMUs), for marine turtles globally.

Conclusions/Significance

The RMU framework is a solution to the challenge of how to organize marine turtles into units of protection above the level of nesting populations, but below the level of species, within regional entities that might be on independent evolutionary trajectories. Among many potential applications, RMUs provide a framework for identifying data gaps, assessing high diversity areas for multiple species and genetic stocks, and evaluating conservation status of marine turtles. Furthermore, RMUs allow for identification of geographic barriers to gene flow, and can provide valuable guidance to marine spatial planning initiatives that integrate spatial distributions of protected species and human activities. In addition, the RMU framework — including maps and supporting metadata — will be an iterative, user-driven tool made publicly available in an online application for comments, improvements, download and analysis.

The impact of conservation on the status of the world's vertebrates

Using data for 25,780 species categorized on the International Union for Conservation of Nature Red List, we present an assessment of the status of the world's vertebrates. One-fifth of species are classified as Threatened, and we show that this figure is increasing: On average, 52 species of mammals, birds, and amphibians move one category closer to extinction each year. However, this overall pattern conceals the impact of conservation successes, and we show that the rate of deterioration would have been at least one-fifth again as much in the absence of these. Nonetheless, current conservation efforts remain insufficient to offset the main drivers of biodiversity loss in these groups: agricultural expansion, logging, overexploitation, and invasive alien species.

Comparative visual function in four piscivorous fishes inhabiting Chesapeake Bay

Maintaining optimal visual performance is a difficult task in photodynamic coastal and estuarine waters because of the unavoidable tradeoffs between luminous sensitivity and spatial and temporal resolution, yet the visual systems of coastal piscivores remain understudied despite differences in their ecomorphology and microhabitat use. We therefore used electroretinographic techniques to describe the light sensitivities, temporal properties and spectral sensitivities of the visual systems of four piscivorous fishes common to coastal and estuarine waters of the western North Atlantic: striped bass (Morone saxatilis), bluefish (Pomatomus saltatrix), summer flounder (Paralichthys dentatus) and cobia (Rachycentron canadum). Benthic summer flounder exhibited higher luminous sensitivity and broader dynamic range than the three pelagic foragers. The former were at the more sensitive end of an emerging continuum for coastal fishes. By contrast, pelagic species were comparatively less sensitive, but showed larger day-night differences, consistent with their use of diel light-variant photic habitats. Flicker fusion frequency experiments revealed significant interspecific differences at maximum intensities that correlated with lifestyle and habitat. Spectral responses of most species spanned 400-610 nm, with significant day-night differences in striped bass and bluefish. Anadromous striped bass additionally responded to longer wavelengths, similar to many freshwater fishes. Collectively, these results suggest that pelagic piscivores are well adapted to bright photoclimates, which may be at odds with the modern state of eutrified coastal and estuarine waters that they utilize. Recent anthropogenic degradation of water quality in coastal environments, at a pace faster than the evolution of visual systems, may impede visually foraging piscivores, change selected prey, and eventually restructure ecosystems.

Comparative visual function in five sciaenid fishes inhabiting Chesapeake Bay

Maintaining optimal visual performance is a difficult task in the photodynamic coastal and estuarine waters in which western North Atlantic sciaenid fishes support substantial commercial and recreational fisheries. Unavoidable tradeoffs exist between visual sensitivity and resolution, yet sciaenid visual systems have not been characterized despite strong species-specific ecomorphological and microhabitat differentiation. We therefore used electroretinographic techniques to describe the light sensitivities, temporal properties, and spectral characteristics of the visual systems of five sciaenids common to Chesapeake Bay, USA: weakfish (Cynoscion regalis), spotted seatrout (Cynoscion nebulosus), red drum (Sciaenops ocellatus), Atlantic croaker (Micropogonias undulatus) and spot (Leiostomus xanthurus). Benthic sciaenids exhibited higher sensitivities and broader dynamic ranges in white light V/logI experiments than more pelagic forms. Sensitivities of the former were at the lower (more sensitive) end of an emerging continuum for coastal fishes. Flicker fusion frequency experiments revealed significant interspecific differences at maximum intensities that correlated with lifestyle and habitat, but no specific differences at dimmer intensities. Spectral responses of most sciaenids spanned 400-610 nm, with significant diel differences in weakfish and Atlantic croaker. Weakfish, a crepuscular predator, also responded to ultraviolet wavelengths; this characteristic may be more useful under less turbid conditions. Collectively, these results suggest that sciaenids are well adapted to the dynamic photoclimate of the coastal and estuarine waters they inhabit. However, the recent anthropogenic degradation of water quality in coastal environments, at a pace faster than the evolution of visual systems, has amplified the importance of characterizing visual function in managed aquatic fauna.

Acoustic pressure and particle motion thresholds in six sciaenid fishes

Sciaenid fishes are important models of fish sound production, but investigations into their auditory abilities are limited to acoustic pressure measurements on five species. In this study, we used auditory brainstem response (ABR) to assess the pressure and particle acceleration thresholds of six sciaenid fishes commonly found in Chesapeake Bay, eastern USA: weakfish(Cynoscion regalis), spotted seatrout (Cynoscion nebulosus),Atlantic croaker (Micropogonias undulatus), red drum (Sciaenops ocellatus), spot (Leiostomus xanthurus) and northern kingfish(Menticirrhus saxatilis). Experimental subjects were presented with pure 10 ms tone bursts in 100 Hz steps from 100 Hz to 1.2 kHz using an airborne speaker. Sound stimuli, monitored with a hydrophone and geophone,contained both pressure and particle motion components. Sound pressure and particle acceleration thresholds varied significantly among species and between frequencies; audiograms were notably flatter for acceleration than pressure at low frequencies. Thresholds of species with diverticulae projecting anteriorly from their swim bladders (weakfish, spotted seatrout,and Atlantic croaker) were typically but not significantly lower than those of species lacking such projections (red drum, spot, northern kingfish). Sciaenids were most sensitive at low frequencies that overlap the peak frequencies of their vocalizations. Auditory thresholds of these species were used to estimate idealized propagation distances of sciaenid vocalizations in coastal and estuarine environments.

Genetic polyandry and sexual conflict in the sandbar shark, Carcharhinus plumbeus, in the western North Atlantic and Gulf of Mexico

To investigate patterns of polyandry in the sandbar shark (Carcharhinus plumbeus), 20 pregnant females were sampled from the western North Atlantic and Gulf of Mexico. Five species-specific microsatellite markers were used to genotype each shark and its litter. Of 20 litters, 17 (85%) were shown to have multiple sires. In multiply sired litters, the estimated minimum number of sires ranged from two to five with an average of 2.3 males per litter. Regression analysis did not demonstrate a significant relationship between female reproductive success and female body size or sire number and female body size. There was a high incidence of reproductive skew noted in litters, and two groups of males with significantly different mean reproductive success were observed. Analyses using Bateman's principles suggest that there is less direct benefit for females that acquire multiple mates than for males who bias paternity within litters. In light of past morphological and behavioural studies, these data suggest that patterns of polyandry in elasmobranchs may be determined by coercive mating, and that breeding behaviour has likely evolved in the context of sexual conflict.

Natal homing in juvenile loggerhead turtles (Caretta caretta)

Juvenile loggerhead turtles (Caretta caretta) from West Atlantic nesting beaches occupy oceanic (pelagic) habitats in the eastern Atlantic and Mediterranean, whereas larger juvenile turtles occupy shallow (neritic) habitats along the continental coastline of North America. Hence the switch from oceanic to neritic stage can involve a trans-oceanic migration. Several researchers have suggested that at the end of the oceanic phase, juveniles are homing to feeding habitats in the vicinity of their natal rookery. To test the hypothesis of juvenile homing behaviour, we surveyed 10 juvenile feeding zones across the eastern USA with mitochondrial DNA control region sequences (N = 1437) and compared these samples to potential source (nesting) populations in the Atlantic Ocean and Mediterranean Sea (N = 465). The results indicated a shallow, but significant, population structure of neritic juveniles (PhiST = 0.0088, P = 0.016), and haplotype frequency differences were significantly correlated between coastal feeding populations and adjacent nesting populations (Mantel test R2 = 0.52, P = 0.001). Mixed stock analyses (using a Bayesian algorithm) indicated that juveniles occurred at elevated frequency in the vicinity of their natal rookery. Hence, all lines of evidence supported the hypothesis of juvenile homing in loggerhead turtles. While not as precise as the homing of breeding adults, this behaviour nonetheless places juvenile turtles in the vicinity of their natal nesting colonies. Some of the coastal hazards that affect declining nesting populations may also affect the next generation of turtles feeding in nearby habitats.

Uterine epithelial-sperm interaction, endometrial cycle and sperm storage in the terminal zone of the oviducal gland in the placental smoothhound, Mustelus canis

The fate of spermatozoa deposited within the female reproductive tract has been described in the smoothhound, Mustelus canis. Evidence of uterine epithelial-sperm interaction is presented, as well as documentation of sperm storage specifically in the terminal zone of the oviducal gland. Sperm fate is correlated with morphology of the endometrial cycle and specificity of storage in the oviducal gland. The endometrium of M. canis undergoes dramatic tissue remodeling associated with gestation. In females harboring fertilized ova or preimplantation yolk-reliant embryos, the uterine epithelium is simple cuboidal with mucous droplets for lubrication. The presence of the embryo elicits a response from the uterus, which becomes modified for nutrient and respiratory exchange into vascular uterine attachment sites that abut the distal aspect of the yolk sac. Areas of the uterus adjacent to the uterine attachment sites are termed paraplacental sites. Uterine attachment sites are simple squamous while the paraplacental epithelium is simple columnar. Paraplacental cells have basal metachromatic vesicles and a dense array of apical cytoplasmic filaments. Immediately postpartum the uterine attachment sites, now termed uterine or placental scars, begin to remodel to a mucous epithelium for the next gestational cycle. Paraplacental cells slough off the apical filamentous portion, and sperm become embedded in the epithelium. Bundled sperm occur throughout gestation in the terminal zone of the oviducal gland. Sperm are not embedded in the terminal zone epithelium as in the uterus. Following sperm release from the uterus, the paraplacental epithelium reverts to a mucous epithelium for the next reproductive cycle. Fertilization is presumed to occur in the anterior oviduct above the oviducal gland. The physiological mechanisms that mediate sperm-uterus attachment, release, and storage in the terminal zone of the oviducal gland are currently under investigation.

Visual acuity thresholds of juvenile loggerhead sea turtles (Caretta caretta): an electrophysiological approach

Visual evoked potentials measure dynamic properties of the visual system by recording transient electric responses of neural tissue identified to correspond to a specific visual stimulus, such as light or a striped grid. In this study, visual evoked potentials were used to test the visual acuity of juvenile loggerhead sea turtles (Caretta caretta) in water. Subject animals were fitted with a Plexiglas goggle filled with filtered seawater. Stimuli of black and white striped gratings were presented to the turtles using a slide projector directing an image onto a screen via a rotatable mirror that shifted the striped pattern laterally one-half cycle. Bioelectric activity was collected using a digital averaging computer and subdermal platinum electrodes, implanted under the head scutes directly above the optic nerve and the contralateral optic tectum. To isolate the response signal from the noise, signal averaging techniques were used when collecting visual evoked potentials. The resulting response waveforms included a robust positive-negative compound that was used to track the turtle's response to visual stimulation. Acuity thresholds for these sea turtles, which were derived from linear regressions analysis of the positive-negative compound amplitudes versus stripe size, ranged from 0.130 to 0.215. This acuity level is comparable to other inshore, shallow water marine species.

Reproduction and food habits of the lined seahorse, Hippocampus erectus (Teleostei: Syngnathidae) of Chesapeake Bay, Virginia

The reproductive and feeding biology of the lined seahorse, Hippocampus erectus, was studied in Chesapeake Bay. Seahorses are monogamous, and males incubate the eggs received from females in a closed brood pouch (= marsupium). Females do not play any parental care after mating. Total sex ratio and the operational sex ratio was strongly skewed toward females. Males and females had similar number of eggs/embryos and hydrated oocytes, respectively. The number of eggs/embryos found in the male brood pouch varied from 97 to 1,552 (fish from 80 to 126 mm TL), whereas the number of hydrated oocytes in female varied from 90 to 1,313 (fish from 60 to 123 mm TL). Both, the number of eggs/embryos and hydrated oocytes were better linearly correlated to total weight than to total length. The small snout and mouth size limits the feeding of the lined seahorse to small prey size. Amphypods were the predominant food items found in the guts, especially Ampithoe longimana, Gammarus mucronatus, and Caprella penantis. The lined seahorse is not abundant in Chesapeake Bay, but keeps a breeding population which is probably brought inside the bay by currents on drifting vegetation. Chances to find a partner may be difficult because of its low abundance, due to turbid waters, and its sedentary behavior.

Effects of insulin-like growth factor-I, corticosterone, and 3,3', 5-tri-iodo-L-thyronine on glycosaminoglycan synthesis in vertebral cartilage of the clearnose skate, Raja eglanteria

Effects of insulin-like growth factor-I (IGF-I), corticosterone, and triiodothyronine (T(3)) on in vitro growth of vertebral cartilage of the clearnose skate, Raja eglanteria, were investigated. Uptake of [(35)S]sulfate in cultured vertebrae was used to characterize glycosaminoglycan (GAG) synthesis and cartilage growth. IGF-I significantly enhanced cartilage growth when concentrations of 1.28 and 12.8 nM were present in the culture system. Corticosterone significantly inhibited vertebral GAG synthesis at concentrations of 1, 10, and 100 nM. This effect was markedly pronounced in cartilage exposed to 1 and 10 nM corticosterone, in which GAG synthesis was virtually ceased. In contrast, T(3) (0.75, 7.5, and 75.0 nM) had no significant effect on sulfate uptake. These data suggest that IGF-I and corticosteroids may play important roles in regulating skeletal growth of elasmobranchs, as they appear to do in other vertebrates. While T(3) does not appear to exert an immediate, direct effect on vertebral growth, it may still influence elasmobranch chondrogenesis over longer culture periods or indirectly through other regulatory pathways. Thus, further information is necessary to characterize the role of thyroid hormones in the skeletal growth of these fishes. The present study is the first in vitro investigation on the hormonal regulation of elasmobranch cartilage growth. As such, the methods described herein provide a useful technique for examining these physiological processes. J. Exp. Zool. 284:549-556, 1999.

Ultrastructure of uterine trophonemata, accommodation for uterolactation, and gas exchange in the southern stingray, Dasyatis americana

The southern stingray, Dasyatis americana, displays aplacental viviparity, embryos being retained in the maternal uterus throughout gestation and initially nourished by the yolk sac contents. During gestation the uterus develops vascularized appendages, trophonemata, that secrete viscous nutrient histotroph that is subsequently ingested by the embryo as it grows to term. There is a 3750% increase in wet mass from the egg to the term fetus. Trophonemata are 1.5 cm long, narrower at the base, and spatulate at the tip. Surface epithelial cells form a pattern of surface cables, each with a small blood vessel at its core. In females containing fertilized eggs, the epithelium is simple and cuboidal. In contrast, in uteri containing late-term fetuses, the epithelium is squamous. Epithelial cells, with periodic acid – Schiff positive cytoplasmic vesicles, form invaginated crypts. Epithelial cells produce proteinaceous, mucous, and lipid secretions, thus we have coined the term uterolactation to describe this phenomenon.

Ultrastructure of fetal alimentary organs: stomach and spiral intestine in the southern stingray, Dasyatis americana

In the fetal southern stingray, Dasyatis americana, both the stomach and spiral intestine function early in development to digest and absorb nutrient histotroph elaborated by uterine villi termed trophonemata. The gastric mucosa consists of a surface columnar mucous epithelium that is confluent with gastric pits or foveolae. Gastric glands are populated by oxynticopeptic and enteroendocrine cells. The surface mucous cells are pyramidal with apical microvilli. Oxynticopeptic cells are low columnar with a distinct and elaborate tubulovesicular system in the apical cytoplasm. Microvilli line the lumen of the gastric glands and cells have elaborate interdigitating lateral folds. Enteroendocrine cells are characterized by basal granules and a prominent rough endoplasmic reticulum. The fetal intestine is filled with bile-tinged viscous fluid. A core of submucosa supports spiral intestinal plicae that form the spiral valve from which villi project. The most prominent characteristic of the cells are enormous supranuclear vesicles formed by coalescence of smaller endocytotic vesicles. The apical cytoplasm has a profusion of smooth tubules, endoplasmic reticulum, and lysosomes. The large vesicles are interpreted as storage depots for continually ingested histotroph. Small vesicles may then bud off to be digested via the lysosomal system.

Proteoglycans from the vertebral cartilage of the clearnose skate, Raja eglanteria: Inhibition of hydroxyapatite formation

Studies were undertaken to examine the importance of organic proteoglycan matrices in the calcification of elasmobranch vertebral cartilage. Proteoglycans were extracted from the vertebral cartilage of the clearnose skate, Raja eglanteria Bosc, with a 3M guanidine hydrochloride/10% EDTA solution. Proteoglycan solutions (12 μg ml(-1)) were effective inhibitors of hydroxyapatite formation in vitro from high concentration calcium phosphate solutions. Inhibition of crystal formation appears to occur through the restriction of phase transformation from a calcium phosphate precursor to hydroxyapatite crystals. The concentration and/or degradation of proteoglycans in elasmobranch vertebral cartilage may have a physiological role in the production of alternating mineral-rich and mineral-poor growth zones, currently used in ageing studies.

Marine turtle middle-ear anatomy

The middle-ear structures from 5 Atlantic Loggerhead (Caretta caretta) and 1 Atlantic Ridley (Lepidochelys kempi) marine turtles from dead specimens found stranded in the lower Chesapeake Bay were dissected and examined superficially and by light microscopy. The marine turtle middle ear is poorly adapted as an aerial receptor in mammalian and reptilian terms. However, it appears well designed as a peripheral component of a bone conduction system. The thick tympanum, while disadvantageous as an aerial receptor, likely enhances low-frequency bone conduction hearing. The columella directly couples the cochlea and saccule so that its movement would stimulate each end organ. Turtle hearing is probably an integration of both outputs.

Marine turtle reception of bone-conducted sound

An individual each of the marine turtles, Caretta caretta and Lepidochelys kempi, were stimulated with audiofrequencies delivered directly to the skull. Startle responses were observed to underwater stimuli of .25 and .5 kc/s. Neural responses to underwater bone-conducted (bc) sound were recorded in another aquatic form, the snapping turtle, Chelydridae serpentina. The morphology of the neural response suggested the involvement of the auditory system in bc responsivity. Bc hearing appears to be a reception mechanism for marine turtles with the skull and shell acting as receiving surfaces. Turtles are capable of receiving the low-frequency spectrum of the natal beach, which may serve as one of the cues in nesting returns.

Biology of the Morid Fish Antimora rostrata in the Western North Atlantic

From otter trawl catches in the Middle Atlantic Bight, blue hake, Antimora rostrata, were found at depths of 790 to at least 2930 m in the Norfolk Canyon area; maximum abundance was between 1300 and 2500 m. Available data indicate that the blue hake is more abundant in the western than the eastern North Atlantic. Males were smaller in average size than females and a skewed sex–depth relationship was found with a larger percentage of the catch in shallower depths being male. In Canadian Atlantic waters A. rostrata live in water at least 500 m shallower. The Middle Atlantic continental slope may serve as a feeding habitat for this species; the reproductive and larval portions of its life history are probably completed in the northern part of its range. Key words: Antimora rostrata, bathymétrie distribution, reproduction