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Context Shark pupping and nursery grounds are essential habitats, yet these areas are undocumented for deepwater species. Young juveniles of black dogfish (Centroscyllium fabricii) were found to be dominant in the Laurentian Channel, prompting an analysis of their distribution in Canadian waters of the Northwest Atlantic. Aims This study documents patterns of distribution by sex and life stage for black dogfish in shelf and slope waters of Canada. Methods Over 40 years of trawl survey data from the Canadian Department of Fisheries and Oceans (DFO) Newfoundland and Labrador Region was analysed to document patterns of distribution of black dogfish by sex and life stage. Key results Free-swimming neonates were found in the Laurentian Channel, along with adult females, including some with pups, indicating that the Laurentian Channel is the pupping grounds for this species. Small black dogfish, highly abundant in the Channel, is largely absent in slope waters, indicating that the Channel is the nursery ground for black dogfish in Canada. Conclusions As they grows, black dogfish individuals undergo a multi-year distributional shift extending over ∼4000 km, originating in the Laurentian Channel out to slope waters, with the largest fish being found furthest from the Channel. No other deep demersal chondrichthyans are known to undergo a progressive migration as they grow, more akin to pelagic sharks where separate pupping–nursery grounds and long-distance migrations are commonly documented. Implications The segregation by life stages shown in the present study differs from previously reported distribution patterns of black dogfish in Greenland and Iceland. Given warm and stable ambient temperatures in the Channel, similar to slope waters, black dogfish is stenothermal, maintaining a narrow thermal profile throughout its life. Identifying the essential habitats of pupping and nursery grounds is crucial to the management and conservation of this species.

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.

Accurate reproductive information is crucial for the effective management of sharks. Here, we used non-lethal methods to evaluate reproductive hormone profiles of blacktip sharks (Carcharhinus limbatus) off the coast of southern Florida (FL) as part of a preliminary investigation of this species’ reproductive patterns in the region. Circulating testosterone concentrations in males ranged from 0.04 to 320.7 ng mL−1, and concentrations peaked during months previously shown to represent peak spermatogenic activity. In females, circulating concentrations of oestradiol (E2) ranged from 12.5 to 941.4 pg mL−1, and progesterone (P4) ranged from 30.1 to 821.2 pg mL−1. E2 peaked during months with peak vitellogenic and ovulatory activity in previous studies; P4 displayed less variability among months. In general, changes in monthly hormone concentrations align well with the timing of reproductive events in C. limbatus in other regions. However, because of low monthly sample sizes and a lack of reproductive status confirmation, the female profiles raise interesting questions about this population’s reproductive cycle that could be explored in future studies. Additional studies should collect larger monthly samples and incorporate supplementary data to provide more insight into the reproductive cycle of this species in southern FL.

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 β-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 β-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.

20 pages, 3 tables, 5 figures.-- Samantha Andrzejaczek ... et al.-- Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC), Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements, Data analysis was funded by the Bertarelli Foundation through the Marine Science program through grants to D.J.C., B.A.B., and S.A. D.J.C. is also funded through Research England, UK. S.A. and B.A.B. thank the Moore Foundation and the Packard Foundation. F.G.-M. thanks the Instituto Politecnico Nacional for fellowships (COFAA, EDI). S.B.W. thanks funding from the Darwin Initiative (DPLUS046). A.D.M.D. acknowledges funding from the Research and Conservation Budget at Georgia Aquarium, including philanthropic gifts from several anonymous donors. K.F. acknowledges funding from the Rolex Awards for Enterprise and the Whitley Fund for Nature

Knowledge of the nutritional requirements of apex predators is key for determining ecological interactions. However, an understanding of how diet is influenced by reproduction, and the consequences of foraging variation on the nutritional status of a predator, is limited. Here, we used short-term dietary markers (plasma and whole-blood fatty acids) integrated with reproductive hormones (17β-estradiol and testosterone) and ultrasonography as a non-lethal approach to investigate the effect of life stage on nutritional status and trophic dynamics of female tiger sharks Galeocerdo cuvier. Despite their generalist feeding behavior, female tiger sharks fed on different food sources and/or modulated their fatty acid metabolism depending on the reproductive context. This suggests some adjustment in their nutritional requirements associated with changes in their reproductive state. Plasma and whole-blood fatty acids indicated distinct dietary sources across life stages, with a high dependence on coastal/benthic food resources during juvenile life stages, and on pelagic/oceanic and reef-associated food resources during adult life stages. Higher percentages of highly unsaturated omega-3 fatty acids found in females during their reproductive cycles suggest the dependency on these fatty acids as a source of metabolic energy during reproduction. A high percentage of arachidonic acid (ARA) found in plasma of gravid females suggests the possibility of a selective diet of ARA-rich prey species and/or selective mobilization of ARA from stored energy during gestation. Based on our findings, we propose a conceptual model of expected changes in nutritional and trophic markers across life stages of female tiger sharks.

Context Over the past decade, the coastal waters off Cape Cod, Massachusetts, have emerged as the only known aggregation site for the white shark (Carcharodon carcharias) in the western North Atlantic. During periods of seasonal residency, white sharks patrol the shoreline in search of pinniped prey, bringing them in close proximity to popular beaches where people recreate. Aim To examine whether white sharks off Cape Cod are more likely to occupy shallow depths (and consequently more likely to overlap with recreational water users) under certain conditions. Methods We deployed short-term, pop-up satellite archival transmitting (PSAT) tags and acoustic transmitters on 14 subadult and adult white sharks off the coast of Cape Cod during the summer and fall of 2017. PSAT tags provided fine-scale depth and temperature data, which were combined with high-resolution location data obtained from an acoustic telemetry array, to identify the depth and temperature preferences of white sharks when resident in the area. Key results Sharks spent the majority (95%) of tracked time at depths of 0–31 m and at temperatures from 8.9°C to 20.7°C. During resident periods along Cape Cod, individuals spent almost half (47%) of their time at depths of less than 4.5 m, but made frequent excursions to mid-shelf depths, alternating between the surf zone and deeper offshore waters. Sharks were slightly more likely to occupy shallow depths at night during the new moon. The relationship between shark depth and lunar phase varied over the course of the day, suggesting the mechanism underlying lunar effects differs among diel periods. Conclusions Although the overall risk posed to humans by white sharks is low, there is a high potential for overlap between white sharks and recreational water users off Cape Cod. The risk of interaction may be slightly higher during periods when local environmental conditions favour the species’ predatory stealth by influencing prey behaviour or detectability. Implications This study provides the first glimpse into the fine-scale vertical habitat use of white sharks off Cape Cod, which can be used to better understand the risk to recreational water users and to inform public safety practices.

Novel, non-lethal approaches are needed to improve our current understanding of the reproductive biology and ecology of the white shark Carcharodon carcharias. Previous studies have demonstrated that concentrations of reproductive hormones in muscle tissue can be used as reliable indicators of reproductive status for many vertebrate species, including elasmobranchs. Here, we applied this method to assess the concentrations of testosterone (T) and estradiol (E2) in muscle biopsies from free-swimming white sharks at a known aggregation site off the coast of Cape Cod, Massachusetts (USA), in the Northwest Atlantic Ocean, to determine whether this technique could be used to evaluate the reproductive status of this species. A total of 14 muscle samples from 13 white sharks (7 males [1 sampled twice], 6 females), ranging in size from 3.3 to 4.2 m total length, were analyzed for this study. T and E2 were present in sufficient amounts to be quantified in 7 of the 8 (87.5%) male and 1 of the 6 (16.7%) female samples, respectively. As expected, most samples collected from immature individuals were below minimum detection thresholds. Hormone concentrations in males presumed to be adults were also generally low, suggesting these individuals were not actively producing sperm at the time of sample collection. Overall, the results herein are similar to those found in other species and indicate that concentrations of hormones in the skeletal muscle of subadult and adult white sharks can provide information on the reproductive status of individuals. This technique could have wide-ranging applications for the study of white shark reproduction in the future.

The Northwest Atlantic (NWA) population of porbeagles Lamna nasus is susceptible to capture in rod-and-reel fisheries and most individuals are discarded alive due to catch and size limits. To estimate post-release survival, pop-off satellite archival tags were attached to porbeagles captured with rod-and-reel. Fourteen tags were deployed, of which 13 transmitted. All sharks for which we had data survived, giving a post-release survival rate of 100%. Following release, 6 individuals remained in surface waters for several hours to days, while 2 individuals immediately resumed normal diving behaviors. For the remaining sharks (n = 5), low tag transmission resolution precluded the detection of fine scale post-release behavior. The duration of initial depth-holding behavior was characterized using a break-point analysis of dive track variance, which suggests porbeagles exhibited a median post-release recovery period of 116 h (10th and 90th percentiles = 68.8 and 280.1 h) following capture and handling. Our preliminary study suggests immature porbeagles are resilient to capture and handling, although more data would provide stronger support for management recommendations.

Between September 2010 and June 2012, a total 291 (166 females and 125 males) blackchin guitarfish Glaucostegus cemiculus were captured by a commercial bottom trawler (F/V Coskun Reis) in Iskenderun Bay, Turkey (northeastern Mediterranean Sea). The total length (L) and total weight (W) of the female and male guitarfish ranged between 32.0-165.0 cm and 88 g-16.68 kg, and 34.3-128.3 cm and 112 g-6.00 kg, respectively. Vertebral age estimates ranged from 0 to 8 years for females and 0 to 5 years for males. The growth models of von Bertanlanffy and Gompertz were fitted to the length at age data using the nonlinear regression method. Model selection was based on the values of the residual standard error and the Akaike's information criterion corrected for small sample size (AIC(C)) associated with each fit. The von Bertalanffy growth model provided the best fitting growth curves for each sex with parameters reaching L-infinity = 187.17 cm, K = 0.195 year(-1), t(0) = -1.38 year for females, and L-infinity = 144.85 cm, K = 0.321 year(-1), t(0) = -1.13 year(-1) for males. The W-L relationship parameters did not differ significantly between sexes, the estimated values of a and b were 0.0018 and 3.11, respectively. By using these values of a and b, and also respective estimates of L-infinity, the values of W-infinity were obtained as 20.53 kg for females and 9.25 kg for males. The overall percentage ratios of females and males in the samples were 57% and 43% respectively.

There has been debate in the literature over the use and success of spatial management zones (i.e. marine protected areas and time/area closures) as policy tools for commercially exploited sharks. The tiger shark (Galeocerdo cuvier) is a highly migratory predator found worldwide in warm temperate and tropical seas, which is caught in multiple US fisheries. We used a spatially explicit modelling approach to investigate the impact of varying spatial management options in the Western North Atlantic Ocean on tiger shark biomass, catch, and distribution, and impacts to other species in the ecosystem. Results suggest that under current management scenarios, tiger shark biomass will increase over time. Model outputs indicate that protecting additional habitats will have relatively minimal impacts on tiger shark biomass, as would increasing or decreasing protections in areas not highly suitable for tiger sharks. However, increasing spatial management protections in highly suitable habitats is predicted to have a positive effect on their biomass. Results also predict possible spill-over effects from current spatial protections. Our results provide insights for evaluating differing management strategies on tiger shark abundance patterns and suggest that management zones may be an effective conservation tool for highly migratory species if highly suitable habitat is protected.

Thorny skate (Amblyraja radiata) have experienced decreasing abundance and range contraction in the Gulf of Maine (GOM) in recent decades. To better understand the extent to which population structure, environmental conditions, and movement ecology may play a role in these disruptions, 128 “mark-report” pop-up satellite tags (mrPATs) and 2195 conventional tags were deployed from 2002 to 2019. Data obtained from 84 mrPATs and 43 conventional tag recaptures [127 individuals: 55 males, 72 females; 32–104 cm total length (TL)] revealed minimum linear horizontal movements of 0.4–46.8 km in all cardinal directions over periods 22–3435 d. There was no relationship between days at liberty, TL, sex, depth, reporting season, or tag type and minimum linear displacement, and no broad seasonal movements were evident. Skates were observed at depths 27–201 m and in water temperatures 2.5–12.5°C, with fluctuations in both depth and temperature evident by season. Given their restricted movements, thorny skate may represent a single stock/population with metapopulation-like structure in the GOM. The pervasiveness of sedentary behaviour may also place the species at risk of localized depletion and climate change but also demonstrates the potential efficacy of spatial closures for promoting population recovery.

The identification of habitats critical to wintering, foraging, and spawning is imperative to the management and recovery of imperiled fishes such as the Atlantic sturgeon Acipenser oxyrinchus oxyrinchus. Atlantic sturgeon are threatened in the Gulf of Maine, and endangered throughout the rest of their range along the United States East coast. While the distribution of Atlantic sturgeon in freshwater and estuarine habitats has been well documented, data on use of marine habitat, particularly in winter months, remains relatively unknown. To better understand the habitat utilization of Atlantic sturgeon during winter, 6 individuals captured at the mouth of the Saco River Estuary (SRE) were fitted with both an external mark report pop-off archival satellite tag (mrPAT) and an internal acoustic transmitter (Vemco V16). Pop-off dates for mrPATs were staggered to occur in pairs on 15 and 30 January and 15 February 2017, with tags recording daily maximum and minimum temperatures while at liberty. All tags lasted the duration of scheduled deployment. Five Atlantic sturgeon appeared to aggregate in Saco Bay within 5 km of their original capture location, while 1 fish moved offshore, where the tag detached 33 km from the mouth of the SRE. The data presented herein suggest that Saco Bay and the surrounding marine environment may serve as wintering habitat for adult Atlantic sturgeon; this is the first direct documentation of such behavior in the Gulf of Maine.

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.

A growing number of studies are using accelerometers to examine activity level patterns in aquatic animals. However, given the amount of data generated from accelerometers, most of these studies use loggers that archive acceleration data, thus requiring physical recovery of the loggers or acoustic transmission from within a receiver array to obtain the data. These limitations have restricted the duration of tracking (ranging from hours to days) and/or type of species studied (e.g., relatively sessile species or those returning to predictable areas). To address these logistical challenges, we present and test a satellite-transmitted metric for the remote monitoring of changes in activity, measured via a pop-off satellite archival tag (PSAT) with an integrated accelerometer. Along with depth, temperature, and irradiance for geolocation, the PSAT transmits activity data as a time-series (ATS) with a user-programmable resolution. ATS is a count of high-activity events, relative to overall activity/mobility during a summary period. An algorithm is used to identify the high-activity events from accelerometer data and reports the data as a count per time-series interval. Summary statistics describing the data used to identify high-activity events accompany the activity time-series. In this study, we first tested the ATS activity metric through simulating PSAT output from accelerometer data logger archives, comparing ATS to vectorial dynamic body acceleration. Next, we deployed PSATs with ATS under captive conditions with cobia (Rachycentron canadum). Lastly, we deployed seven pop-off satellite archival tags (PSATs) able to collect and transmit ATS in the wild on adult sandbar sharks (Carcharhinus plumbeus). In the captive trials, we identified both resting and non-resting behavior for species and used logistic regression to compare ATS values with observed activity levels. In captive cobia, ATS was a significant predictor of observed activity levels. For 30-day wild deployments on sandbar sharks, satellites received 57.4–73.2% of the transmitted activity data. Of these ATS datapoints, between 21.9 and 41.2% of records had a concurrent set of temperature, depth, and light measurements. These results suggest that ATS is a practical metric for remotely monitoring and transmitting relative high-activity data in large-bodied aquatic species with variable activity levels, under changing environmental conditions, and across broad spatiotemporal scales.

To fuel the high energetic demands of reproduction, vertebrates employ different tactics of resource use. Large sharks exhibit long gestation periods and have relatively few well-developed young, which likely incurs high energetic costs. However, information on the relationship between the reproductive and energetic states for most shark species is lacking. In the present study, we used a noninvasive approach to assess relationships among reproductive stage, plasma triglyceride levels, body condition, and circulating reproductive hormones in free-ranging female tiger sharks (Galeocerdo cuvier). A total of 57 sharks were sampled (19 immature, 15 mature/nongravid, and 23 gravid). Circulating plasma triglycerides did not significantly differ among female tiger sharks of different reproductive stages, but body condition values were significantly higher for mature/nongravid sharks ([Formula: see text]) compared with gravid ([Formula: see text]) and immature ([Formula: see text]) sharks. For gravid and mature/nongravid sharks, no significant correlations existed among values of reproductive hormones, plasma triglycerides, and body condition. However, for immature sharks, estradiol values were negatively correlated with body condition values. Additionally, progesterone levels were positively correlated with testosterone levels in immature females. Our results suggest that this large generalist predator may not necessarily be easily characterized as a pure capital breeder, as has been previously hypothesized for ectotherms, but may rely on a mix of energy stores and opportunistic feeding to support reproduction. We present several hypotheses to explain these patterns and discuss our results in terms of energetic reproductive strategies.

Thorny skate (Amblyraja radiata) remain one of the most overfished species in the Gulf of Maine (GOM) despite being designated as a prohibited (zero-possession, mandatory release) species by the New England Fishery Management Council in 2003. To better understand the extent to which discard mortality (DM) occurring after incidental capture in the GOM groundfish bottom trawl fishery may be impeding recovery, 75 individuals (55–94 cm total length, TL) were tagged with pop-up satellite archival transmitting (PSAT) tags and monitored for up to 28 days following capture under representative commercial trawl fishing practices. Data recovered from 61 PSAT-tagged skate were analysed with a longitudinal survival analysis to estimate DM and identify influential capture-related variables. DM rate was a function of TL, with larger skates (>70 cm; DM = 16.5%) experiencing lower mortality than smaller conspecifics (55–70 cm; DM = 24.5%). From our results, we estimate annual thorny skate DM in the GOM groundfish bottom trawl fishery to be 79.2 ± 0.2 mt, which accounts for

Discard mortality (DM) estimates are vitally important to fisheries management. Commercial fishery DM estimates, for example, can help calculate total fishing mortality and biologically acceptable catch limits. The winter skate, Leucoraja ocellata, is the only species within the US portion of the western North Atlantic that is targeted in the skate wing fishery. However, due primarily to fishery regulations, this species is also routinely discarded at sea when daily quotas are reached. While already examined in mobile fishing gears (i.e. bottom otter trawls), DM has not been addressed for the western North Atlantic skate species captured in the sink gillnet fishery, and a conservative 50% DM is used across the species of the skate complex in the management processes. Given this data gap, we estimate the DM of winter skate in sink gillnets under standard commercial fishing conditions. The study methods employed address the issue of cryptic mortality (drop out of dead skates from the gear and depredation prior to retrieval), which can bias DM estimates low for bycatch in passive gear. The degree of injury sustained during capture and handling was found to be a statistically significant predictor of mortality. Overall mean DM rates reached an asymptote within 170 h of captivity, with estimates of 11% and 17% for females and males, respectively. Based on these results, the species appears more resilient to sink gillnet capture and release than previously thought. However, cryptic fishing mortality appeared to be high for extended soak times and likely represents an important focus of future research and management actions.

Due primarily to regulatory factors, skates (family Rajidae) account for nearly half the total bycatch discarded during commercial fishing operations in the U.S. portion of the Northwest Atlantic Ocean. In this region the New England scallop dredge fishery has the second highest skate discard rate; however, no information regarding their resiliency to interaction with this gear type exists. To gain insight into species-specific mortality rates, 295 tows were conducted throughout six research cruises (2012–2013 fishing season), with a total of 4216 skates (little skate, Luecoraja erinacea, winter skate, Leucoraja ocellata, and barndoor skate, Dipturus laevis) evaluated and scored using reflex impairment and injury (i.e., overt physical trauma) indicators. To quantify mortality rates associated with these indicators, 334 skates were retained in an on-deck refrigerated flow-through seawater system and monitored every six-hours until the end of a trial. This study also assessed the effect of fishing conditions/practices and individual traits on post-release mortality. Data suggest that species-specific differences exist wherein winter skate are likely the most resilient (45.4% mortality) to capture and handling, little skate have a moderate capacity to deal with these pressures (62.7% mortality), and barndoor skate appear to be the most susceptible (99.9% mortality). In addition, little and winter skate mortality rates were both influenced by tow duration, while fishing depth and temperature gradient had an effect on little skate and air exposure on winter skate.

Identification of potential critical habitat, seasonal distributions, and movements within and between river systems is important for protecting the Gulf of Maine (GOM) distinct population segment of Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus. To accomplish these objectives, we captured Atlantic Sturgeon from four GOM rivers (Penobscot, Kennebec system, Saco, and Merrimack) and tagged 144 individuals (83.3–217.4 cm TL) internally with uniquely coded acoustic transmitters. Tagged fish were detected from 2006 to 2014 by primary receiver arrays that were deployed in the four GOM rivers or were detected opportunistically on a secondary group of receivers deployed within the GOM and along the continental shelf. Tagged Atlantic Sturgeon were documented at three spawning areas in the Kennebec system in June and July, including an area that became accessible in 1999 when Edwards Dam was removed. The majority (74%) of tagged fish were detected in the estuaries of the four GOM rivers, primarily in Ma...

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&rsquo, 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 &deg, C, 22 or 30 &deg, and 9, 13, or 15 &deg, 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 &deg, 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&ndash, 105%, p &lt, 0.05) and decreases in hypoxia tolerance (60&ndash, 84% increases in critical oxygen pressure, 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.

Intraspecific variability in life-history patterns is well documented in elasmobranchs, and defining regionally specific parameters is essential for proper management and sustainability of species. Studies on the reproductive biology of finetooth sharks (Carcharhinus isodon) have noted a potential disparity in periodicity within North American waters. To better define regional variability, the current study collected 1490 finetooth sharks (831 female, 659 male) from the northern Gulf of Mexico. The size-at-maturity was determined to be 995- and 961-mm fork length for females and males respectively. In males, the peak gonadosomatic index (GSI) in March and presence of semen in the seminal vesicles in April suggested spermatogenesis occurs from March to April. In females, ovulation occurred from May to June, with a peak GSI occurring in May and maximum vitellogenic follicle diameter occurring in May and June. Gestation was found to be 11–12 months, with parturition occurring in May and June and a mean brood size was 3.8±0.1 embryos. Of the 50 females examined during the ovulatory period, 32 exhibited annual and 18 exhibited biennial reproductive periodicity. The results from this study will be impactful, because regionally distinct reproductive parameters can now be considered for future assessments.

This comparative study of the radial testes of sexually mature thresher sharks (Alopias vulpinus) and shortfin mako sharks (Isurus oxyrinchus) describes the histology of the three-tiered network of sperm-carrying ductules in the testis and the lymphomyeloid tissue associated with it, namely the epigonal organ. In both species, a testis → epigonal gradient was evident regarding the thickness of the ductule epithelial lining and subepithelial investment of connective tissue. Ductules straddling the testis-epigonal border often displayed luminal leukocytes and various signs of regression, including the progressive thickening of the ductule epithelial lining, dissolution of the cytoplasm, and loss of normal histoarchitecture. In Isurus, large amorphous areas formed due to the fusion of neighboring regressing ductules. The epigonal organ of Alopias additionally revealed circular degenerative sperm-containing, Hassall-like bodies with either a degenerate or cellular appearance, the latter the result of cell proliferative activity (as shown by proliferating cell nuclear antigen (PCNA) immunohistochemistry) in an expanding outer border comprising cells with intensely PCNA immunoreactive slender and oblong nuclei. The latter cells exhibited a periphery-to-center transformation of their nuclei, at which stage they were PCNA-negative and most likely in a terminally differentiated state as they phagocytized the cell debris in the degenerate core. Intermediate stages of these circular bodies were a rarity. The relationship between these degenerate bodies, and the common occurrence of blind pockets in the epithelial linings and non-apoptosis-related degenerate patches in the apical cytoplasmic regions of the irregular shaped ductules in Alopias is unclear, and needs further elucidation. Anat Rec, 299:1435-1448, 2016. © 2016 Wiley Periodicals, Inc.

In recent years, the recreational contribution to the total catch of Atlantic cod (Gadus morhua) in the Gulf of Maine (GOM) has increased with recreational discards outnumbering recreational landings by 2:1. However, the discard mortality (DM) rate of cod released in the recreational fishery remains poorly understood, thus contributing to the uncertainty in stock assessments and fishery management plans. The current study examined the capture-related factors most detrimental to cod DM in the GOM recreational rod-and-reel fishery. Atlantic cod (n = 640; 26.0–72.0 cm) were angled from June–October 2013 on southern Jeffreys Ledge in the western GOM using fishing gear representative of the local recreational fishery. A subset (n = 136) was also tagged with pressure-sensing acoustic transmitters before being released into an acoustic receiver array (n = 31) deployed to monitor survival up to 94 days. To properly model DM up to the fishery-wide level, all cod were visually assessed for capture-related injuries according to a four-level injury score index. Mean tackle-specific DM rates of 15.4 and 21.2% were estimated for bait- and jig-captured cod, respectively, with an overall 16.5% mean DM rate for the 2013 GOM recreational cod fishery. Twenty-nine cod tagged with acoustic transmitters were identified as dead, where the majority (∼90%) died within 16 h post-capture. Upon evaluation with a specifically adapted parametric survival analysis, greater incidence of mortality was attributed to the capture and handling process (rather than release) for moderately and severely injured cod. Based on the capture-related factors associated with the highest injury rates, we recommend minimizing fight and handling times, avoiding areas with small cod, educating inexperienced anglers, and favouring bait over jigs to mitigate mortality. Results will continue to inform the development of fishery management plans and enhance survival through dissemination of “best practice” techniques to fishery stakeholders.

Advancing our knowledge of the reproductive biology and mating systems of free- ranging sharks is inherently challenging. The large size and mobility of the specimens are just a few of the problems that make such studies complicated, and in some respects, impractical. The tiger shark Galeocerdo cuvier is a large, roving, apex predator found in many oceans throughout the world. Although their nomadic nature is primarily linked to large-scale migrations, these sharks can also display site fidelity. One site where this is known to occur is at Tiger Beach, Bahamas. Unique to the waters of this area is the consistent sighting of large females. While the sex-specific use of the area remains unknown, the shallow, warm environment could represent a critical habitat for reproductive events. To investigate the reproductive biology of tiger sharks at Tiger Beach, 65 individuals were opportunistically sampled between 2011 and 2014. Reproductive status of captured females (n = 59) was assessed with ultrasonography and by measuring circulat- ing sex steroid hormones (progesterone, testosterone and estradiol). Our results indicate that Tiger Beach is a high-use site for female tiger sharks of mixed life stages. The results also suggest that Tiger Beach may function as a refuge habitat, allowing females to reach maturity free from male mating harassment, as well as functioning as a gestation ground where gravid females can benefit from year-round calm warm waters, which may reduce the gestation period and accelerate embryo development.

The post-release mortality of discarded fish can represent an additional source of mortality that is important to understand for effective marine fisheries management. To best estimate these mortality rates under near-natural conditions, a refrigerated flow-through seawater system was developed for short-term holding experiments at-sea aboard commercial fishing vessels, using accessory tanks containing heat exchanging coils cooled by an ice slurry. Ice was added to these tanks in one to two-hour intervals based on the cooling requirement. This system was capable of maintaining temperatures within one degree Celsius of target conditions for 93–96% of operation, creating an environment where post-release mortality could be evaluated without additional thermal stress.

Overfishing and habitat loss have reduced Pseudopleuronectes americanus (Winter Flounder) populations within the Gulf of Maine (GOM), and despite strict management regulations, abundance is still low. As the GOM continues to warm, there is need to characterize Winter Flounder movements in estuaries to better understand essential habitat use. To characterize movements and habitat use of Winter Flounder, we tagged 17 juvenile flounder (115–170 mm) with acoustic transmitters (Vemco V7-2x) and monitored them using passive tracking over a 4-month period between July and November 2017 in the Saco River Estuary (SRE) in southern Maine. Movement within the SRE was highly variable, with cumulative movements of individual tracked flounder varying between 0 m (e.g., detected only at the release site) and 17,016 m. Tagged flounder were most often present in moderate (15–20 °C) temperatures and salinities (18–26 ppt), and were rarely observed in the highest temperatures (>20 °C) and salinities (>26 ppt). Movements upstream and downstream by flounder appeared to be tidally driven, with most downstream movements occurring during ebb tides and upstream movements during incoming tides. In addition, large flounder moved further away from freshwater, while small flounder either stayed within the river mouth's jetties or moved upstream. The speeds of flounder movements among receiver locations (mean = 4.49 body lengths per second, SE = 0.85) were much faster than expected for flatfish, potentially facilitated by use of tides. The GOM populations of Winter Flounder may benefit from management of juvenile habitat as environmental conditions change.

The latest stock assessment for the dusky shark, Carcharhinus obscurus, in the western North Atlantic Ocean indicates the population is overfished and experiencing overfishing. As part of a rebuilding plan, the commercial and recreational retention of dusky sharks has been prohibited since 2000. Despite this prohibition, dusky sharks are bycatch in multiple fisheries, including the pelagic longline fishery; however, post-release mortality (PRM) rates have not been empirically determined for this gear. Herein we estimated PRM of dusky sharks captured by the US pelagic longline fleet in the western North Atlantic Ocean utilizing pop-up satellite archival transmitting (PSAT) tags. One hundred and twenty three dusky sharks were captured on commercial pelagic longline gear and time on the hook, based on hook timer data, ranged from 0.8 to 8.1 h (4.3 ± 0.28 h). No at-vessel mortality (AVM) was observed for any dusky sharks in this study. Prior to release, 50 PSAT LIFE tags (Lotek Inc.) were attached to dusky sharks (females n = 12, 209 ± 8 cm FL; males n = 4, 198 ± 7 cm FL; unknown sex n = 34, 214 ± 7 cm FL) to assess PRM rates in the pelagic longline fishery during a 30 day attachment period. Forty-three of the 50 deployed tags reported data with deployment times ranging from 1 to 28 days (11.2 ± 9.8 days). Four dusky sharks were in poor condition at release and two individuals suffered PRM, which occurred within two hours after release. Total mortality rate (AVM + PRM) in the current study was 5.1%, far below estimates reported for bottom longline gear (˜97%), and reinforces the notion that PRM should be evaluated by species, season, and gear type.