Search

Knowledge of blue marlin, Makaira nigricans, movement patterns across a range of spatiotemporal scales is important for understanding the ecology of this epipelagic fish, informing responsible management strategies, and understanding the potential impacts of a changing ocean climate to the species. To gain insight into movement patterns, we analyzed data from 66 blue marlin satellite-tagged between 2001 and 2021 throughout the North Atlantic. We recorded migrations connecting west and east Atlantic tagging locations, as well as long-term residency within small sub-regions. Blue marlin showed a pattern of latitudinal migration, occupying lower latitudes during cooler months and higher latitudes in warmer months. Diving data indicate blue marlin primarily inhabited a shallow vertical habitat with deeper diving associated with higher sea surface temperatures and dissolved oxygen content. Consistent patterns in diel vertical habitat use support the hypothesis that these fish are visual hunters, diving deeper during the day, as well as dawn, dusk, and full moon periods. The wide-ranging movements of blue marlin indicate that traditional spatial management measures, such as static marine reserves, are unlikely to be effective in reducing the fishing mortality of this species. Longer tag deployment durations are required to delineate its annual and multi-annual migratory cycle.

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

In tunas, the slow-twitch red muscle, which has an elevated temperature, powers thunniform locomotion, a stiff-bodied swimming style. The anatomical placement and operating temperatures of red muscle vary widely among teleosts: in tunas, the red muscle is located centrally in the body, adjacent to the spine, and maintains an elevated temperature. In the majority of ectothermic teleosts, red muscle is located laterally in the body, adjacent to the skin, and operates at ambient temperature. The specialized physiology and biomechanics of red muscle in tunas are often considered important adaptations to their high-performance pelagic lifestyle; however, the mechanics of how muscular work is transmitted to the tail remains largely unknown. The red muscle has a highly pennate architecture and is connected to the spine through a network of bones (epicentral bones) and long tendons (posterior oblique tendons). The network of long tendons has been hypothesized to enhance the power transmitted to the tail. Here, we investigate the morphology and biomechanics of the tuna's red muscle and tendons to determine whether elasticity is exploited to reduce the cost of transport, as is the case in many terrestrial vertebrates. To address this question, we evaluate two hypotheses: (1) tendons stretch during red-muscle-actuated swimming and (2) tendons comprise the primary load transmission pathway from the red muscle to the spine. To evaluate these hypotheses, we measured the mechanical properties of the posterior oblique tendons and performed novel dissections to estimate the peak force that the red muscle can generate. The force-generating capacity of the red muscle is calculated to be much greater than the load-bearing capacity of the posterior oblique tendons. Thus, the long tendons likely stretch under force from the red muscle, but they are not strong enough to be the primary force transmission pathway. These results suggest that other pathways, such as serial load transmission through the red muscle myomeres to the great lateral tendon and/or the anterior oblique tendons to the skin, transmit appreciable force to the tail.

Bluefin tunas are highly specialized fish with unique hydrodynamic designs and physiological traits. In this study, we present results in a captive population that demonstrate strong effects of ambient temperature on the tail beat frequency and swimming speed of a pelagic fish in both pre- and post-prandial states. We measured the responses of a ram ventilator, the Pacific bluefin tuna (Thunnus orientalis), after digestion of a meal to explore the impacts of the metabolic costs of digestion on behavior and respiration. A combination of respirometry, physiological biologging of visceral temperatures, and activity monitoring with accelerometry were used to explore the metabolic costs of digestion and the impacts on ventilation and swimming speed. Experiments were conducted at temperatures that are within the metabolic optimum for Pacific bluefin tuna (17 °C), and at a second temperature corresponding to the upper distributional limit of the species in the California Current (24 °C). Warmer temperatures resulted in higher tail-beat frequency and greater elevation of body temperature in pre-prandial Pacific bluefin tuna. Specific dynamic action (SDA) events resulted in a significant postprandial increase in tail-beat frequency of ~0.2 Hz, compared to pre-prandial levels of 1.5 Hz (17 °C) and 1.75 Hz (24 °C), possibly resulting from ventilatory requirements. Data of fish exercised in a swim-tunnel respirometer suggest that the observed increase in tail-beat frequency comprise 5.5 and 6.8% of the oxygen demand during peak SDA at 24 °C and 17 °C respectively. The facultative increase in swimming speed might increase oxygen uptake at the gills to meet the increasing demand by visceral organs involved in the digestive process, potentially decreasing the available energy of each meal for other metabolic processes, such as growth, maturation, and reproduction. We hypothesize that these post-prandial behaviors allow tuna to evacuate their guts more quickly, ultimately permitting fish to feed more frequently when prey is available.

Discerning behaviours of free-ranging animals allows for quantification of their activity budget, providing important insight into ecology. Over recent years, accelerometers have been used to unveil the cryptic lives of animals. The increased ability of accelerometers to store large quantities of high resolution data has prompted a need for automated behavioural classification. We assessed the performance of several machine learning (ML) classifiers to discern five behaviours performed by accelerometer-equipped juvenile lemon sharks (Negaprion brevirostris) at Bimini, Bahamas (25°44′N, 79°16′W). The sharks were observed to exhibit chafing, burst swimming, headshaking, resting and swimming in a semi-captive environment and these observations were used to ground-truth data for ML training and testing. ML methods included logistic regression, an artificial neural network, two random forest models, a gradient boosting model and a voting ensemble (VE) model, which combined the predictions of all other (base) models to improve classifier performance. The macro-averaged F-measure, an indicator of classifier performance, showed that the VE model improved overall classification (F-measure 0.88) above the strongest base learner model, gradient boosting (0.86). To test whether the VE model provided biologically meaningful results when applied to accelerometer data obtained from wild sharks, we investigated headshaking behaviour, as a proxy for prey capture, in relation to the variables: time of day, tidal phase and season. All variables were significant in predicting prey capture, with predations most likely to occur during early evening and less frequently during the dry season and high tides. These findings support previous hypotheses from sporadic visual observations. Electronic supplementary material The online version of this article (10.1007/s00227-018-3318-y) contains supplementary material, which is available to authorized users.

During the 2010 Deepwater Horizon incident, the continuous release of crude oil from the damaged Macondo 252 wellhead on the ocean floor contaminated surface water habitats for pelagic fish for more than 12 weeks. The spill occurred across pelagic, neritic and benthic waters, impacting a variety of ecosystems. Chemical components of crude oil are known to disrupt cardiac function in juvenile fish, and here we investigate the effects of oil on the routine metabolic rate of chub mackerel, Scomber japonicus. Mackerel were exposed to artificially weathered Macondo 252 crude oil, prepared as a Water Accommodated Fraction (WAF), for 72 or 96 h. Routine metabolic rates were determined pre- and post-exposure using an intermittent-flow, swim tunnel respirometer. Routine energetic demand increased in all mackerels in response to crude oil and reached statistical significance relative to unexposed controls at 96 h. Chemical analyses of bile from exposed fish revealed elevated levels of fluorescent metabolites, confirming the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in the exposure WAF. The observed increase in metabolic demand is likely attributable to the bioenergetic costs of contaminant detoxification. These results indicate that short-term exposure (i.e. days) to oil has sub-lethal toxicity to mackerel and results in physiological stress during the active spill phase of the incident.

Pacific bluefin tuna (Thunnus orientalis) is a highly migratory, commercially valuable species potentially vulnerable to acoustic noise generated from human activities which could impact behavior and fitness. Although significant efforts have been made to understand hearing abilities of fishes, the large size and need to continuously swim for respiration have hindered investigations with tuna and other large pelagic species. In this study, Pacific bluefin tuna were trained to respond to a pure tone sound stimulus ranging 325-800 Hz and their hearing abilities quantified using a staircase psychophysical technique. Hearing was most sensitive from 400 to 500 Hz in terms of particle motion (radial acceleration -88 dB re 1 m s(-2); vertical acceleration -86 dB re 1 m s(-2)) and sound pressure (83 dB re 1 μPa). Compared to yellowfin tuna (Thunnus albacares) and kawakawa (Euthynnus affinis), Pacific bluefin tuna has a similar bandwidth of hearing and best frequency, but greater sensitivity overall. Careful calibration of the sound stimulus and experimental tank environment, as well as the adoption of behavioral methodology, demonstrates an experimental approach highly effective for the study of large fish species in the laboratory.

Purpose. To assess complement factors and T lymphocyte activation subset abnormalities in patients with thrombotic antiphospholipid syndrome (APS) as potential biomarkers for development of clinical complications.Methods. We assessed C3, C4, factor B concentrations (nephelometry), complement haemolytic functional activity (CH100, radial immune diffusion), and the activation status of CD4+ and CD8+ T-cells (three-colour flow cytometry) in patients with thrombotic APS. Antiphospholipid (aPL) positive patients without APS-related clinical criteria, systemic lupus erythematosus (SLE) patients, and healthy individuals were evaluated as controls. A clinical followup was performed to assess the potential relationship between the immunological parameters and development of APS-related complications.Results. Lower concentrations of C3 and higher levels of CD8+DR+ cells were risk factors for development of APS-related complications during followup, including rethrombosis and neuropsychiatric symptoms. Patients with diagnosed thrombotic APS had significantly lower levels of C3, C4, and CH100 as well as higher percentages of activated CD4+DR+ and of CD8+DR+ T-cells than healthy controls but similar to that observed in autoimmune disease controls.Conclusion. Lower C3 and C4 complement levels and higher percentages of CD8+DR+ T-cells were observed in thrombotic APS patients. The potential role of these abnormalities as biomarkers of clinical outcome warrants further evaluation in a multicenter study.

Tunas possess a range of physiological and mechanical adaptations geared towards high-performance swimming that are of considerable interest to physiologists, ecologists and engineers. Advances in biologging have provided significant improvements in understanding tuna migrations and vertical movement patterns, yet our understanding of the locomotion and swimming mechanics of these fish under natural conditions is limited. We equipped Atlantic bluefin tuna (Thunnus thynnus) with motion-sensitive tags and video cameras to quantify the gaits and kinematics used by wild fish. Our data reveal significant variety in the locomotory kinematics of Atlantic bluefin tuna, ranging from continuous locomotion to two types of intermittent locomotion. The tuna sustained swimming speeds in excess of 1.5 m s−1(0.6 body lengths s−1), while beating their tail at a frequency of approximately 1 Hz. While diving, some descents were entirely composed of passive glides, with slower descent rates featuring more gliding, while ascents were primarily composed of active swimming. The observed swimming behaviour of Atlantic bluefin tuna is consistent with theoretical models predicting such intermittent locomotion to result in mechanical and physiological advantages. Our results confirm that Atlantic bluefin tuna possess behavioural specializations to increase their locomotory performance, which together with their unique physiology improve their capacity to use pelagic and mesopelagic habitats.

Consumption rates of marine predators are vital to assessing their trophic impacts and potential consequences of fisheries removal and habitat alteration, yet are rarely estimated. Standard metabolic rates were estimated for juvenile brown stingrays, Dasyatis lata, and used as input parameters for a bioenergetics model to predict consumption rates. Temperature and mass had significant effects on metabolic rates. The energy budget of juvenile brown stingrays was heavily weighted toward metabolism, accounting for 66 % of consumed energy. Growth accounted for 7 % of the energy budget indicating very slow growth potentially due to limited food resources. Population consumption rates suggest potential for strong top-down effects on prey populations due to stingray predation. This study suggests the use of Kāne‘ohe Bay as a nursery habitat for juvenile brown stingrays is a trade-off between increased juvenile survival through predator avoidance and a late age at first maturity due to slow growth rates resulting from low prey availability.

Identification of nursery habitats and knowledge of the trophic ecology and habitat use of juvenile fishes within these habitats are fundamental in developing sound management and con- servation strategies. The brown stingray Dasyatis lata is a large benthic predator that inhabits the coastal waters of Hawai'i. Although abundant in these ecosystems, little is known about its basic eco - logy. Stomach content, bulk and amino acid stable isotope analyses were used to assess diet and habitat use of juvenile brown stingrays and to examine the possibility of competitive interactions with juvenile scalloped hammerhead sharks Sphyrna lewini that are sympatric with brown stingrays in K¯ ane'ohe Bay, Oahu. Based on stomach contents, brown stingrays fed almost exclusively on crus- taceans. An ontogenetic shift in stingray diet and an increase in relative trophic position (TP) were apparent from stomach content and stable isotope analysis. Stingray bulk δ 13 C and δ 15 N values indi- cated long-term foraging fidelity to subregions of the bay. Use of K¯ ane'ohe Bay as a nursery habitat was supported by nitrogen isotopic analysis of individual amino acids from stingray muscle samples. Our results clearly demonstrated that stingrays foraged within the bay for the majority of their juve- nile lives then shifted to offshore habitats with the onset of sexual maturity. Trophic enrichment fac- tors used to estimate TPs from amino acid analysis in previous studies may underestimate TPs in elas- mobranchs owing to urea retention for osmoregulation. Potential prey resources were partitioned between stingrays and juvenile scalloped hammerhead sharks, and TP estimates from each analyti- cal method indicated that juvenile scalloped hammerhead sharks forage on higher TP prey than do juvenile brown stingrays. These results show that the study of foraging ecology and habitat use of marine animals can greatly benefit from integrating traditional stomach content and bulk stable isotopic analyses with nitrogen isotopic analyses of individual amino acids.

SUMMARYShark cage diving is both popular and controversial, with proponents citing educational value and non-extractive use of natural resources and opponents raising concerns about public safety and ecological impacts. Logbook data collected 2004–2008 from two Oahu (Hawaii) shark cage diving operations were analysed to determine whether such voluntary records provide useful insights into shark ecology or ecotourism impacts. Operators correctly identified common shark species and documented gross seasonal cycles and long-term trends in abundance of Galapagos (Carcharhinus galapagensis), sandbar (Carcharhinus plumbeus) and tiger sharks (Galeorcerdo cuvier). Annual cycles in shark abundance may indicate seasonal migrations, whereas long-term trends suggest gradual exclusion of smaller sandbar sharks from cage diving sites. Numerically dominant (> 98%) Galapagos and sandbar sharks are rarely implicated in attacks on humans. Negligible impact on public safety is supported by other factors such as: (1) remoteness of the sites, (2) conditioning stimuli that are specific to the tour operations and different from inshore recreational stimuli and (3) no increase in shark attacks on the north coast of Oahu since cage diving started. Tracking studies are required to validate logbook data and to determine whether sharks associated with offshore cage diving travel into inshore areas used for in-water recreation.

Specific dynamic action (SDA), the increase in metabolic expenditure associated with consumption of a meal, represents a substantial portion of fish energy budgets and is highly influenced by ambient temperature. The effect of temperature on SDA has not been studied in yellowfin tuna (Thunnus albacares, Bonnaterre 1788), an active pelagic predator that occupies temperate and subtropical waters. The energetic cost and duration of SDA were calculated by comparing routine and post-prandial oxygen consumption rates. Mean routine metabolic rates in yellowfin tuna increased with temperature, from 136 mg O2 kg(-1)h(-1) at 20 °C to 211 mg O2 kg(-1)h at 24 °C. The mean duration of SDA decreased from 40.2h at 20 °C to 33.1h at 24 °C, while mean SDA coefficient, the percentage of energy in a meal that is consumed during digestion, increased from 5.9% at 20 °C to 12.7% at 24 °C. Digestion in yellowfin tuna is faster at a higher temperature but requires additional oxidative energy. Enhanced characterization of the role of temperature in SDA of yellowfin tuna deepens our understanding of tuna physiology and can help improve management of aquaculture and fisheries.

Natural killer (NK, CD3(-)CD56(+)/CD16(+)) and NKT-like cells (CD3(+)CD56(+)/CD16(+)) activity is considered among the key factors for reproductive success. In the absence of immunological screening, beneficial effects of intravenous immunoglobulin (IVIG) in preventing recurrent reproductive failure (RRF) have not been reported. Here, we analyse the IVIG influence on pregnancy success in women with RRF and circulating NK or/and NKT-like cells expansion.One hundred fifty-seven women with previous recurrent miscarriage and/or recurrent implantation failure after in vitro fertilization were consecutively studied. Sixty-four patients with CD56(+) cell expansion, no apparent underlying disease and who maintained their desire to conceive were selected. Forty of them received IVIG during pregnancy.Overall, the clinical pregnancy rate for the women under IVIG therapy was 92.5% and the live birth rate was 82.5%. Significantly lower pregnancy and live birth rates (25% and 12.5%, respectively) were observed for the patients with recurrent pregnancy loss and NK/NKT-like cells expansion without IVIG. After three cycles of IVIG, NK cell percentages decreased significantly and these values persisted throughout gestation.Intravenous immunoglobulin therapy for women with RRF and NK or NKT-like cell expansion was a safe and beneficial therapeutic strategy that associated with high clinical pregnancy and live birth rates.

Empirical data on the abundance and habitat preferences of coral reef top predators are needed to evaluate their ecological impacts and guide management decisions. We used longline surveys to quantify the shark assemblage at French Frigate Shoals (FFS) atoll from May to August 2009. Fishing effort consisted of 189 longline sets totaling 6,862 hook hours of soak time. A total of 221 sharks from 7 species were captured, among which Galapagos (Carcharhinus galapagensis, 36.2%), gray reef (Carcharhinus amblyrhynchos, 25.8%) and tiger (Galeocerdo cuvier, 20.4%) sharks were numerically dominant. A lack of blacktip reef sharks (Carcharhinus melanopterus) distinguished the FFS shark assemblage from those at many other atolls in the Indo-Pacific. Compared to prior underwater visual survey estimates, longline methods more accurately represented species abundance and composition for the majority of shark species. Sharks were significantly less abundant in the shallow lagoon than adjacent habitats. Recaptures of Galapagos sharks provided the first empirical estimate of population size for any Galapagos shark population. The overall recapture rate was 5.4%. Multiple closed population models were evaluated, with Chao M(h) ranking best in model performance and yielding a population estimate of 668 sharks with 95% confidence intervals ranging from 289-1720. Low shark abundance in the shallow lagoon habitats suggests removal of a small number of sharks from the immediate vicinity of lagoonal islets may reduce short-term predation on endangered monk seal (Monachus schauinslandi) pups, but considerable fishing effort would be required to catch even a small number of sharks. Additional data on long-term movements and habitat use of sharks at FFS are required to better assess the likely ecological impacts of shark culling.

Coral reef habitats in the Papahānaumokuākea Marine National Monument (PMNM) are characterized by abundant top-level predators such as sharks and jacks. The predator assemblage is dominated both numerically and in biomass by giant trevally (Caranx ignobilis) and Galapagos sharks (Carcharhinus galapagensis). A lower diversity of predatory teleosts, particularly groupers and snappers, distinguishes the PMNM from other remote, unfished atolls in the Pacific. Most coral reef top predators are site attached to a “home” atoll, but move extensively within these atolls. Abundances of the most common sharks and jacks are highest in atoll fore reef habitats. Top predators within the PMNM forage on a diverse range of prey and exert top-down control over shallow-water reef fish assemblages. Ecological models suggest ecosystem processes may be most impacted by top predators through indirect effects of predation. Knowledge gaps are identified to guide future studies of top predators in the PMNM.

We report the results of a series of experiments to test the utility of acceleration data-loggers for determining the energy expenditure of juvenile hammerhead sharks ( Sphyrna lewini ). In one experiment, three sharks were instrumented with miniature acceleration data-loggers and swum in a Brett-style respirometer at a range of speeds. For all three sharks, significant linear relationships were obtained between mean oxygen consumption (M · o 2 ) and Partial Dynamic Body Acceleration in the lateral and dorso-ventral axes (PDBA y , z ) with high predictive power ( r 2 > 0.71). In a second experiment, PDBA was measured for sharks swimming freely in circular tanks. The free-swimming sharks exhibited wide ranges of PDBA y , z ; routine swimming was characterised by low PDBA y , z (0.01–0.12 g) whereas unsteady swimming, (especially fast-start swimming of > 1 g) was characterised by high PDBA y , z . Despite initial evidence of linearity in the oxygen consumption vs. PDBA relationship, incorporating previous estimates of standard metabolic rate of hammerhead sharks suggests a non-linear fit. Further work is needed to establish the exact shape of the relationship beyond the narrow range of speeds that hammerhead pups could be exercised in this study, particularly the low swimming speeds which are frequently observed in free-swimming animals.

The authors acknowledge the National Oceanic and Atmospheric Administration (National Marine Sanctuaries Program), University of Hawaii Sea Grant and the State of Hawaii (Department of Land and Natural Resources) for providing funding to support a variety of shark research projects that collectively made this study possible. Tiger sharks (Galecerdo cuvier) are apex predators characterized by their broad diet, large size and rapid growth. Tiger shark maximum size is typically between 380 & 450 cm Total Length (TL), with a few individuals reaching 550 cm TL, but the maximum size of tiger sharks in Hawaii waters remains uncertain. A previous study suggested tiger sharks grow rather slowly in Hawaii compared to other regions, but this may have been an artifact of the method used to estimate growth (unvalidated vertebral ring counts) compounded by small sample size and narrow size range. Since 1993, the University of Hawaii has conducted a research program aimed at elucidating tiger shark biology, and to date 420 tiger sharks have been tagged and 50 recaptured. All recaptures were from Hawaii except a single shark recaptured off Isla Jacques Cousteau (24 degrees 13'17 '' N 109 degrees 52'14 '' W), in the southern Gulf of California (minimum distance between tag and recapture sites = approximately 5,000 km), after 366 days at liberty (DAL). We used these empirical mark-recapture data to estimate growth rates and maximum size for tiger sharks in Hawaii. We found that tiger sharks in Hawaii grow twice as fast as previously thought, on average reaching 340 cm TL by age 5, and attaining a maximum size of 403 cm TL. Our model indicates the fastest growing individuals attain 400 cm TL by age 5, and the largest reach a maximum size of 444 cm TL. The largest shark captured during our study was 464 cm TL but individuals >450 cm TL were extremely rare (0.005% of sharks captured). We conclude that tiger shark growth rates and maximum sizes in Hawaii are generally consistent with those in other regions, and hypothesize that a broad diet may help them to achieve this rapid growth by maximizing prey consumption rates. Publisher PDF

Hearing thresholds for three pairs of 1 m long Pacific bluefin tuna (Thunnus orientalis) were measured utilizing operant conditioning procedure with a food reward and a staircase psychophysical technique. Fish, swimming at 2-3 m/sec, quickly learned to approach the feed when they heard a sound. Measurements were made at the Tuna Research and Conservation Center (Stanford University) in a 9.14 m diameter, 1.65 m deep indoor cylindrical tank. The acoustic stimulus was produced by radially oriented piezoelectric line sources centered at the bottom of the tank which produced a circumferentially uniform sound field. The acoustics of the tank was thoroughly characterized for both acoustic pressure and particle motion using hydrophones and two neutrally buoyant accelerometers with response axes oriented in the radial and vertical directions. Thresholds, expressed in terms of pressure and particle acceleration were obtained at six sinusoidal frequencies between 325 Hz and 800 Hz, a range that was limited by source and tank acoustics. The lowest mean threshold for the three fish pairs, expressed in terms of acoustic pressure, was 83 dB re 1 µPa at 500 Hz. [Supported in part by ONR/CNR Challenge Grant: "Mitigation of flow noise effects by fish"]

Baseline data on life-history characteristics of elasmobranchs are often lacking before fisheries exploitation, hindering successful management and conservation of affected species. Age, growth and maturity estimates were determined for the brown stingray, Dasyatis lata, an abundant benthic predator in Hawai’i’s coastal ecosystems, from an unfished population off Oahu, Hawai’i. Age estimates ranged from 0 to 28 years for females and from 0 to 25 years for males. Annual growth-band deposition was verified through marginal increment and centrum edge analysis, as well as recapture of two stingrays marked with oxytetracycline. Multiple growth models were fitted to disk width (DW) and weight-at-age data and evaluated for biological realism and statistical fit. Logistic growth functions best described growth of male and female stingrays, whereas no support was found for von Bertalanffy growth models. Females attained larger sizes (L∞) and exhibited lower growth coefficients (k) than did males. Median size and age at first maturity was estimated to be 104.9 cm DW (15 years) for females and 74.9 cm DW (8.3 years) for males. These life-history characteristics highlight the importance of obtaining baseline data before fisheries are established and indicate that any fishery for brown stingrays should be managed using conservative management strategies.

Sharks are found in association with main Hawaiian Island ocean fish farms more frequently and at higher densities than is typical for coastal Hawaiian waters. Sharks attracted to fish farms could potentially threaten human water users, interact negatively with other fisheries, and seasonal migrations could be disrupted if individuals become entrained around farms throughout the year. We hypothesised that smaller coastal species would reside near farms, whereas more wide-ranging species would associate with farms only for short periods. We utilised passive acoustic telemetry to monitor the movements and behaviour of sandbar (Carcharhinus plumbeus) and tiger (Galeocerdo cuvier) sharks adjacent to two open ocean fish farms in Hawaii. Approximately half the tagged sandbar sharks showed site fidelity to the farms, with some individuals being detected repeatedly for 2.5 years. Sandbar sharks moved seasonally to the west coast of Oahu, suggesting that fish farms are not disrupting natural seasonal cycles in this species. Tiger sharks tagged near the cages were more transient, and showed much shorter residence times although some individuals returned sporadically to the cages over the 3-year period. Ocean fish cages appear to aggregate sandbar sharks, but are only ‘visited’ by tiger sharks. Although threats to public safety are probably minimal, the ecological effects of aggregating top-predators are still unknown.