Lectin binding to pectoral fin of neonate little skates reared under ambient and projected-end-of-century temperature regimes.

The glycosylation of macromolecules can vary both among tissue structural components and by adverse conditions, potentially providing an alternative marker of stress in organisms. Lectins are proteins that bind carbohydrate moieties and lectin histochemistry is a common method to visualize microstructures in biological specimens and diagnose pathophysiological states in human tissues known to alter glycan profiles. However, this technique is not commonly used to assess broad-spectrum changes in cellular glycosylation in response to environmental stressors. In addition, the binding of various lectins has not been studied in elasmobranchs (sharks, skates, and rays). We surveyed the binding tissue structure specificity of 14 plant-derived lectins, using both immunoblotting and immunofluorescence, in the pectoral fins of neonate little skates (Leucoraja erinacea). Skates were reared under present-day or elevated (+5°C above ambient) temperature regimes and evaluated for lectin binding as an indicator of changing cellular glycosylation and tissue structure. Lectin labeling was highly tissue and microstructure specific. Dot blots revealed no significant changes in lectin binding between temperature regimes. In addition, lectins only detected in the elevated temperature treatment were Canavalia ensiformis lectin (Concanavalin A) in spindle cells of muscle and Ricinus communis agglutinin in muscle capillaries. These results provide a reference for lectin labeling in elasmobranch tissue that may aid future investigations.

A novel intrauterine satellite transmitter to identify parturition in large sharks.

Determining where and when animals give birth is critical for establishing effective conservation management that protects vulnerable life stages (e.g., pregnant females and newborns) and places (e.g., nursery grounds). To date, this information has been elusive in the case of highly migratory sharks in the wild. Here, we report on the deployment a of novel intrauterine satellite tag implanted in two highly mobile apex predators, the tiger shark (Galeocerdo cuvier) and the scalloped hammerhead (Sphyrna lewini), that remotely documented the location and timing of birth by a highly migratory oceanic animal in the wild. This novel technology will be especially valuable for the protection of threatened and endangered shark species, where protection of pupping and nursery grounds is a conservation priority.

Physiological markers suggest energetic and nutritional adjustments in male sharks linked to reproduction.

Energetic condition is one of the most important factors that influence fitness and reproductive performance in vertebrates. Yet, we lack evidence on how energetic states change in response to reproduction in large marine vertebrates. In the present study, we used a non-lethal approach to assess relationships among reproductive stage, circulating steroid hormones (testosterone and relative corticosteroid levels), plasma fatty acids, and the ketone body ß-hydroxybutyrate in male sharks of two species with divergent ecologies, the benthic nurse shark (Ginglymostoma cirratum) and the epipelagic blacktip shark (Carcharhinus limbatus). We found higher relative corticosteroid levels in adult nurse sharks during the pre-mating period and in blacktip sharks during the mating period. Higher levels of ß-hydroxybutyrate were found in adult nurse sharks during the mating period, but concentrations of this ketone body did not significantly vary across reproductive stages in blacktip sharks. We also detected reduced percentages of essential fatty acids during the mating period of both nurse and blacktip sharks. Taken together, our findings suggest that nurse and blacktip sharks differ in their energetic strategy to support reproduction, however, they likely rely on physiologically important fatty acids during mating, to support spermatogenesis.

Metabolic and nutritional condition of juvenile tiger sharks exposed to regional differences in coastal urbanization.

How varying levels of human activity, such as proximity and size of the nearest market (i.e., market gravity), influence the nutritional ecology and physiological condition of highly migratory marine predators is poorly understood. In the present study, we used a non-lethal approach to compare the concentration of metabolic hormones (i.e. corticosteroids and thyroid hormones) and plasma fatty acids between juvenile female tiger sharks (Galeocerdo cuvier) sampled in two areas of the subtropical north Atlantic, which differed markedly in their levels of coastal urbanization, Florida and the Bahamas (high versus low, respectively). We hypothesized that juvenile female tiger sharks sampled in water surrounding high coastal urbanization (Florida), would exhibit evidence of lower prey quality and higher energetic demands as compared to individuals sampled in relatively less urbanized areas of Northern Bahamas. Results revealed that relative corticosteroid levels (a proxy for energy mobilization) were higher in juvenile female tiger sharks sampled in Florida; however, no differences were found in concentrations of thyroid hormones (proxies of energetic adjustments) between the two locations. We found higher percentages of omega-3 polyunsaturated fatty acids (indicative of high prey quality) in juvenile tiger sharks from Florida, whereas higher percentages of bacterial markers (often indicative of domestic sewage effluent) were detected in the individuals sampled in the Bahamas. Taken together, these findings do not suggest that the differences in nutritional quality and metabolic condition found between the two sampling locations can be fully attributed to foraging in areas exposed to differing levels of urbanization. We speculate that these patterns may be due to the highly migratory nature and generalist feeding strategy of this species, even at the juvenile life stage, as well as proximity of sampling locations from shore.

Combined Effects of Acute Temperature Change and Elevated pCO2 on the Metabolic Rates and Hypoxia Tolerances of Clearnose Skate (Rostaraja eglanteria), Summer Flounder (Paralichthys dentatus), and Thorny Skate (Amblyraja radiata).

Understanding how rising temperatures, ocean acidification, and hypoxia affect the performance of coastal fishes is essential to predicting species-specific responses to climate change. Although a population's habitat influences physiological performance, little work has explicitly examined the multi-stressor responses of species from habitats differing in natural variability. Here, clearnose skate (Rostaraja eglanteria) and summer flounder (Paralichthys dentatus) from mid-Atlantic estuaries, and thorny skate (Amblyraja radiata) from the Gulf of Maine, were acutely exposed to current and projected temperatures (20, 24, or 28 °C; 22 or 30 °C; and 9, 13, or 15 °C, respectively) and acidification conditions (pH 7.8 or 7.4). We tested metabolic rates and hypoxia tolerance using intermittent-flow respirometry. All three species exhibited increases in standard metabolic rate under an 8 °C temperature increase (Q10 of 1.71, 1.07, and 2.56, respectively), although this was most pronounced in the thorny skate. At the lowest test temperature and under the low pH treatment, all three species exhibited significant increases in standard metabolic rate (44-105%; p < 0.05) and decreases in hypoxia tolerance (60-84% increases in critical oxygen pressure; p < 0.05). This study demonstrates the interactive effects of increasing temperature and changing ocean carbonate chemistry are species-specific, the implications of which should be considered within the context of habitat.

Risk of extinction of a unique skate population due to predation by a recovering marine mammal.

Benefitting from reduced harvesting and an end to culling, many marine mammals are now recovering from past overexploitation. These recoveries represent important conservation successes but present a serious conservation problem when the recovering mammals are predators of species of conservation concern. Here, we examine the role of predation by recovering grey seals (Halichoerus grypus) in the near-extinction of a unique skate population in the southern Gulf of St. Lawrence (sGSL) in Atlantic Canada. Winter skate (Leucoraja ocellata) in the sGSL are distinct from winter skate elsewhere and may represent an endemic species. Their adult abundance has declined by 98% since 1980, and these skates are now detectable in only a small fraction of their former range. Population modeling indicates that the ongoing collapse of this population is due to increases in the natural mortality of adults. Based on model projections, this population would be extinct by mid-century if its current rate of productivity were to persist. A second population model incorporated predation by grey seals. Model estimates of skate consumption by seals were consistent with historical and recent estimates of the contribution of skates to grey seal diets. The estimated consumption accounted for the increases in the natural mortality of adult skates. A Type III functional response for grey seals preying on winter skate emerged from the model results. This indicates that, when skate abundance is very low, grey seals are expected to switch to alternate prey, resulting in declines in the mortality of skates due to predation. Consequently, contrary to projections at current productivity, winter skate are expected to be trapped at very low abundance in a "predator pit" instead of declining to extinction. Nonetheless, extinction risk would remain very high at the very small population size in the predator pit. Our results emphasize the need for an ecosystem-based approach to the management of living resources in this ecosystem.

The effect of capture and handling stress in Lophius americanus in the scallop dredge fishery.

Capture and handling stress studies are considered a primary research priority, particularly for species and fisheries where discard rates are high, and/or for overfished stocks and species of concern. Lophius americanus, a commercially valuable finfish in New England, constitutes the second highest bycatch species within the sea scallop dredge fishery. Despite its commercial importance, no data exists on the capture and handling stress of monkfish for any gear type. Given these shortcomings, our goals were to evaluate the stress response of monkfish captured in scallop dredge gear by evaluating physical, behavioural and physiological responses to scallop fishing practices. While 80% of monkfish displayed little to no physical trauma, behavioural and physiological assessment indicated high levels of stress, especially as air exposure and tow duration increased. This finding suggests that the manifestation of stress in monkfish may be a cryptic response necessitating further research in addition to estimates of post-release mortality rates to appropriately advise fisheries management regarding the mortality of monkfish bycatch in the sea scallop fishery.

Using circulating reproductive hormones for sex determination of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) in the Saco River estuary, Maine.

The Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is a long-lived, anadromous fish species ranging from Labrador, CA to Florida, USA. In the Saco River, located in the Gulf of Maine, this species was not present during a survey study ending in 1982, but was found inhabiting the estuary in 2007. Although the reason for the return of this sturgeon to this river system remains unknown, research on basic life-history information is necessary to facilitate the conservation of this federally protected species. Given the conservation status of the species, the present study used circulating sex steroid hormones to determine the sex of 288 Atlantic sturgeon captured between 2012 and 2014 in the Saco River estuary located in the Gulf of Maine. Overall, the sex was determined for 93% of Atlantic sturgeon sampled. Mean hormone values were similar to other Atlantic sturgeon reproductive studies. The findings indicate the validity of sex steroid hormones as a singular method for sex determination in wild Atlantic sturgeon. Results also indicated a likely 1:1 (male:female) sex ratio in the system, except in 2014 when a 1:3 ratio was observed. It is not believed that the Saco River estuary is used for spawning, as several impassable dams block access to spawning habitat. However, this area might provide crucial foraging for growth and development of juveniles and a habitat for adults forgoing spawning.

The use of satellite tags to redefine movement patterns of spiny dogfish (Squalus acanthias) along the U.S. east coast: implications for fisheries management.

Spiny dogfish (Squalus acanthias) are assumed to be a highly migratory species, making habitual north-south migrations throughout their northwestern Atlantic United States (U.S.) range. Also assumed to be a benthic species, spiny dogfish stock structure is estimated through Northeast Fisheries Science Center (NEFSC) bottom-trawl surveys. Recent anomalies in population trends, including a recent four-fold increase in estimated spawning stock biomass, suggest alternative movement patterns could exist for this shark species. To obtain a better understanding of the horizontal and vertical movement dynamics of this species, Microwave Telemetry pop-up satellite archival X-Tags were attached to forty adult spiny dogfish at the northern (Gulf of Maine) and southern (North Carolina) extents of their core U.S. geographic range. Reconstructed geolocation tracks ranging in lengths from two to 12 months suggest that the seasonal migration patterns appear to be local in nature to each respective northern and southern deployment site, differing from previously published migration paradigms. Differences in distance and direction traveled between seasonal geolocations possibly indicate separate migratory patterns between groups. Kernel utilization distribution models also suggest strong separate core home ranges. Significant differences in seasonal temperature and depths between the two regions further substantiate the possibility of separate regional movement patterns between the two groups. Vertical utilization also suggests distinct diel patterns and that this species may not utilize the benthos as previously thought, potentially decreasing availability to benthic gear.

Using estradiol and progesterone concentrations to assess individual variability in the reproductive cyclicity of captive female little skates, Leucoraja erinacea, from the western Gulf of Maine.

In the current study, plasma steroid hormones were used to assess the individual variability of Leucoraja erinacea over the course of 12 months, in hopes of further defining its reproductive cycle. No statistical differences in hormone concentrations were observed between the isolated and non-isolated female skates. Monthly E2 concentrations ranged from 1,430 pg ml(-1) in August to 3,940 pg ml(-1) in March, indicating the presence of mature ovarian follicles and supporting the conclusions from previous studies that L. erinacea is capable of reproducing year-round. Concentrations of E2 were significantly elevated or depressed during some months (February, March, June, July, August, and September) of the year, suggesting that reproductive activity may vary over the annual cycle. Even though monthly P4 concentrations were highly variable, ranging from 82 pg ml(-1) in November to 816 pg ml(-1) in September, no significant reproductive peaks were observed. In addition, a persistently large variation in E2 and P4 concentrations, indicative of reproductive asynchrony within (mean CV 62% and CV 69%, respectively) and between (mean range CV 78 and 125%, respectively) individual skates, was observed throughout the study. Collectively, the continually high E2 concentrations and variability in both hormones observed in the current study are indicative of an oviparous species that reproduces actively throughout the year. However, the weekly sampling frequency revealed that plasma E2 concentrations, not P4, were more useful to assess reproductive status in asynchronous continuously breeding oviparous elasmobranchs.

Assessing reproductive status in elasmobranch fishes using steroid hormones extracted from skeletal muscle tissue.

Elasmobranch fishes (sharks, skates, and rays) are particularly susceptible to anthropogenic threats, making a thorough understanding of their life history characteristics essential for proper management. Historically, elasmobranch reproductive data have been collected by lethal sampling, an approach that is problematic for threatened and endangered species. However, recent studies have demonstrated that non-lethal approaches can be as effective as lethal ones for assessment of the reproductive status of an animal. For example, plasma has been used to examine concentrations of steroid hormones. Additionally, skeletal muscle tissue, which can be obtained non-lethally and with minimal stress, can also be used to quantify concentrations of steroid hormones. Skeletal muscle progesterone, testosterone, and estradiol concentrations were determined to be statistically significant indicators of reproductive status in the oviparous Leucoraja erinacea, the yolk-dependent viviparous Squalus acanthias, and the yolk-sac placental viviparous Rhizoprionodon terraenovae. The results of the present study demonstrate that steroid hormones present in non-lethally harvested skeletal muscle tissue can be used as reliable indicators of reproductive status in elasmobranchs.

Seasonal variations in the physiological stress response to discrete bouts of aerial exposure in the little skate, Leucoraja erinacea.

Aerial exposure and acute thermal stress have been shown to elicit profound physiological disruptions in obligate water-breathing teleosts. However, no study has investigated these responses in an elasmobranch. To address this, venous blood samples were collected and evaluated from little skates (Leucoraja erinacea) subjected to discrete aerial exposure durations (0, 15, and 50 min) coupled with differing abrupt thermal changes (gradient between seawater and air; winter: ΔT=-3 °C; summer: ΔT=+9 °C) in two distinct laboratory studies. In general, blood acid-base properties (e.g. decline in pH; elevation in PCO(2)) and select metabolites (elevated whole-blood lactate) and electrolytes (elevated plasma K(+)) were significantly disrupted by aerial exposure, and were most disturbed after skates were exposed to air for 50 min. However, the magnitude of the blood acid-base perturbations, metabolic contribution to the resulting blood acidosis, elevations to ionic and metabolic parameters, and delayed mortality were more extreme during the summer study, suggesting that acute thermal stress exacerbates the physiological impairments associated with aerial exposure in little skates. Conversely, a reduced thermal gradient (from seawater to air) may attenuate the magnitude of metabolic and ionic perturbations, resulting in a high physiological threshold for coping with extended aerial exposure.