Pop-up Satellite Archival Tags Research Articles

Diel vertical movements of a coastal predator, the roosterfish (

The roosterfish (Nematistius pectoralis) is a piscivorous predator targeted extensively in recreational fisheries throughout the eastern tropical Pacific; however, its biology is poorly understood. To address these shortcomings, we investigated vertical habitat use and behaviour of roosterfish in coastal Panama using pop-up satellite archival tags. Nearly 5000 h of vertical movement data across 274 days from five fish showed that roosterfish largely used the upper 10 m and 20 m of the water column during the night-time and daytime respectively, and rarely left the mixed layer. Roosterfish diving behaviour showed a clear diurnal pattern, with oscillatory dives beginning during dawn and continuing through dusk. Accelerometer data showed that this period was also associated with a sharp increase in activity during dawn and a decrease around sunset. Whereas previous work in shallow systems (<20 m) with limited structure showed that roosterfish were vertically active sporadically throughout the day and mostly during crepuscular periods, our study showed that in a habitat with continuous structure, roosterfish were continuously vertically active from dawn till dusk, possibly because foraging behaviours were limited by light levels rather than prey-congregating structure. Such changes in dive patterns illustrate how habitat influences behaviour and the importance of studying organisms throughout their range.

Ocean-entry timing and marine habitat-use of Canadian Dolly Varden: Dispersal among conservation, hydrocarbon exploration, and shipping areas in the Beaufort Sea

Conservation and management of anadromous salmonids are enhanced by understanding timing, spatial extent, and occupied depths and temperatures in marine feeding habitats. We examined ocean-entry timing and marine habitat-use, and their association with environmental conditions (e.g., sea-ice and sea-surface temperatures (SSTs)) of anadromous Dolly Varden (Salvelinus malma malma) from the Canadian Arctic using pop-up satellite archival tags (PSAT) and data storage tags. Using this information, we evaluated the extent tagged fish occupied offshore (>5 km) habitats, and their proximity to a marine protected area (MPA) and areas of potential threats in the Canadian Beaufort Sea. Ocean-entry by tagged fish using the western Mackenzie Delta for freshwater migration occurred approximately mid-June (range = 8–26 June) and closely followed landfast sea-ice break-up based on satellite imagery. While at sea, fish predominately occupied surface waters (<2 m) at SSTs of 5–10 °C. PSAT end-locations were 37–152 km offshore, typically near the sea-ice edge, greatly extending previously reported distances from shore in the Alaskan Beaufort Sea. The spatial extent of offshore dispersal by Dolly Varden is likely influenced by SSTs and sea-ice conditions, and the physical properties of the Mackenzie River plume (e.g., turbidity), which extends preferred temperatures farther from shore. In relatively cooler years characterized by later sea-ice breakup and a summer sea-ice margin situated closer to shore, fish spent more time in nearshore than offshore habitats (51.7% vs. 48.3%) compared to warmer years (12.6% vs. 87.5%). Furthermore, fish typically occupied shallower offshore mean depths (2.2 m vs. 3.4 m) of the water column and experienced colder mean water temperatures (5.1 °C vs. 7.4 °C) in cooler versus warmer years. Dolly Varden were found within or adjacent to hydrocarbon lease areas and shipping lanes, and may be vulnerable to threats associated with these activities. Although PSATs reported outside of the MPA boundaries, which are situated adjacent to the Mackenzie Delta, occupancy in spring was inferred during ocean-entry and while transitioning to offshore areas. This first study to describe how environmental conditions influence marine distribution of Canadian Dolly Varden together with their proximity to anthropogenic threats is relevant for assessing impacts of climate change and future development.

Movements, Habitat Use, and Diving Behavior of Shortfin Mako in the Atlantic Ocean

The shortfin mako is one of the most important shark species caught in Atlantic Ocean pelagic fisheries. Given increasing concerns for the stock status of the species, the present study was designed to fill gaps in the knowledge of habitat use and movement patterns of shortfin mako in the Atlantic Ocean. From 2015 to 2019, 53 shortfin makos were tagged with pop-up satellite archival tags within the North, Central, and Southwest Atlantic Ocean, with successful transmissions received from 34 tags. Generally, sharks tagged in the Northwest and Central Atlantic moved away from tagging sites showing low to no apparent residency patterns, whereas sharks tagged in the Northeast and Southwest Atlantic spent large periods of time near the Canary Archipelago and Northwest Africa, and over shelf and oceanic waters off southern Brazil and Uruguay, respectively. These areas showed evidence of site fidelity and were identified as possible key areas for shortfin mako. Sharks spent most of their time in temperate waters (18–22°C) above 90 m; however, data indicated the depth range extended from the surface down to 979 m, in water temperatures ranging between 7.4 and 29.9°C. Vertical behavior of sharks seemed to be influenced by oceanographic features, and ranged from marked diel vertical movements, characterized by shallower mean depths during the night, to yo-yo diving behavior with no clear diel pattern observed. These results may aid in the development of more informed and efficient management measures for this species.

Seasonal migratory patterns of Pacific cod (Gadus macrocephalus) in the Aleutian Islands

BackgroundPacific cod (Gadus macrocephalus) is an ecologically important species that supports a valuable commercial fishery throughout Alaska waters. Although its life history includes seasonal movement for spawning and feeding, little is known about its movement ecology. Here, we present results from the first study to use pop-up satellite archival tags (PSATs) to track the within-year movements of Pacific cod to understand their potential seasonal movement patterns within the Aleutian Islands. This study was part of a cooperative research project; tagging was conducted onboard commercial vessels during the winter fishing season while Pacific cod were aggregated to spawn in the central Aleutian Islands.ResultsOf the 36 PSATs deployed, we were able to obtain movement data from 13 Pacific cod that were at liberty between 60 and 360 days. We determined that three tagged Pacific cod were predated on by marine mammals and three were recaptured by the commercial fishery. Geolocation models were produced for four migrating individuals. Eight Pacific cod moved to a productive foraging ground near Seguam Island located 64 to 344 km from their release site and presumed spawning ground within a few weeks of their release. These movements indicate that some Pacific cod in the Aleutian Islands undergo seasonal migration. Three Pacific cod remained near their release locations (within 50 km) for more than 75 days suggesting the existence of partial migration in the population. Two Pacific cod undertook larger movements (378 and 394 km) during which they swam over deep passes and crossed several management boundaries highlighting the potential connectedness of Pacific cod throughout the Aleutian Islands.ConclusionsThis study provided important initial insights into the seasonal movement patterns of Pacific cod in the Aleutian Islands. Most tracked Pacific cod (77%) undertook migrations in the middle of March (64–394 km) from their winter spawning areas to summer foraging areas, but a few individuals remained in their capture location suggesting a partial migration strategy. Their ability to cross deep passes that were previously seen as potential barriers to movement has expanded our understanding of population connectivity.

Horizontal and vertical migration behavior of silver-phase Japanese eels in coastal, pelagic and spawning areas observed by pop-up satellite archival tags

Pop-up satellite archival tags (PSAT) have been used to study the mysterious open ocean spawning migrations of several anguillid eel species including the Japanese eel, Anguilla japonica. To compare migration behaviors of Japanese eels in each general geographic region of their spawning migration, 7 silver eels (852–992 cm, 1095–1809 g) were tracked with PSATs and their swimming behaviors in regions of east of Japan, south of the Ogasawara Islands, and in their spawning area was analyzed. Three eels released from coastal Japan migrated east or southeastward, likely including some transport by the Kuroshio in the initial phase of the spawning migration. An eel released from the coast of Japan changed swimming depths as it crossed meanders and different water masses on different sides of the eastward flow of the Kuroshio Extension. An eel released west of the Ogasawara Islands moved mostly southward from the release site toward the spawning area where an eel released in the spawning area showed very stable diel vertical migrations (DVM). Five eels showed stable DVM for 9–47 days (60.0–72.1%) of the tracking periods (14–69 days), and 2 other eels showed abnormal behaviors. The daily rhythms of DVM behavior transitioned between shallower/warmer water at night (12.0–535.2 m/12.5–24.5 °C) and deeper/colder water during daytime (593.0–941.0 m/4.5–9.5 °C). The swimming depths of 5 eels had positive correlations with lunar age, moon altitude and sun altitude. Eels experienced almost the same daytime minimum water temperature (5.7 ± 0.98 °C) in the 3 areas regardless of depth, suggesting that they stop descending when they reach a temperature of approximately 5 °C. The ascending and descending occurred between around sunset and dusk, and dawn and sunrise, respectively. Three eels were ingested by predators near dawn (5:05–6:35) at depths of 119.5, 59, and 423.5 m when the eels start the decent phase of their DVM. Potential predators were estimated to be fish that have heat conservation ability such as tuna and swordfish based on rapid increases in recorded temperature. This study suggests that Japanese eels probably use similar DVM behaviors regardless of the location or environmental conditions during their spawning migration and that the swimming depths are determined by light and thermal environments. These behaviors are likely essential for predation avoidance.

Redefining the oceanic distribution of Atlantic salmon

Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured at sea at West Greenland. Individuals migrated further north and east than previously reported and displayed increased diving activity near oceanographic fronts, emphasizing the importance of these regions as feeding areas. The oceanic distribution differed among individuals and populations, but overlapped more between geographically proximate than distant populations. Dissimilarities in distribution likely contribute to variation in growth and survival within and among populations due to spatio-temporal differences in environmental conditions. Climate-induced changes in oceanographic conditions will alter the location of frontal areas and may have stock-specific effects on Atlantic salmon population dynamics, likely having the largest impacts on southern populations.

Three-Dimensional Movements and Habitat Selection of Young White Sharks (Carcharodon carcharias) Across a Temperate Continental Shelf Ecosystem

As highly mobile predators with extensive home ranges, some shark species often utilize a continuum of habitats across the continental shelf ranging from the surf zone to the open ocean. For many species, these cross-shelf distributions can change depending on ontogeny or seasonal conditions. Recent research has confirmed a white shark (Carcharodon carcharias) summer nursery off Long Island, New York; however, habitat characterization of this nursery has not yet been conducted nor has fine-scale analysis of vertical behavior. Between 2016 and 2019, 21 young-of-the-year and juvenile white sharks were fitted with satellite and acoustic tags to examine distribution and selection for a suite of oceanographic variables during their late summertime (i.e., August to October) residence in the New York Bight. Horizontal position estimates were used to extract a suite of environmental measurements via remote sensing platforms and were linked with vertical profiles to produce three-dimensional movements for a subset of individuals also fitted with pop-up satellite archival tags (n = 7). Sharks exhibited horizontal movements parallel to Long Island’s southern shoreline and coastal New Jersey, with distances from 0.1 to 131.5 km from shore. Log-likelihood chi-square analyses determined selection for waters with underlying bathymetry of 20–30 m, sea surface temperatures between 20.0 and 22.0°C, sea surface salinities between 31.0 and 32.0 ppt, and chlorophyll-a concentrations between 2.0 and 8.0 mg⋅m–3. Multiple individuals also traversed the mid- to outer shelf region after leaving the Montauk tagging area. Vertical depth profiles illustrated oscillations between the surface and 199 m of water, with an average swimming depth of 9.2 ± 8.9 m. Water column temperatures during these oscillations ranged between 7.9 and 26.2°C (mean = 19.5 ± 2.0°C) with several individuals traversing highly stratified regions presumably associated with a mid-shelf cold pool adjacent to the Hudson Shelf Valley. These results suggest young white sharks exhibit connectivity between the immediate shoreline and mid-continental shelf region, where they play important ecological roles as predators on a variety of species. Our study improves characterization of essential fish habitat for young white sharks and provides new insights into their reliance on this productive continental shelf ecosystem.

Application of a parametric survival model to understand capture-related mortality and predation of yellowfin tuna (Thunnus albacares) released in a recreational fishery

Distinguishing the cause and magnitude of capture-related mortality (CRM) in fishes is important for effective management. To better understand CRM in yellowfin tuna (Thunnus albacares) released in the recreational troll fishery off the United States east coast, 48 fish (76–127 cm curved fork length, CFL) were monitored for up to 86 days postrelease with survivorship pop-up satellite archival tags. Recovered data indicated 40 fish were alive at the time of tag detachment and eight died, including six from predation, from 0 to 30 days postrelease. Survival model variants were constructed to independently estimate the rates of immediate capture and handling (CH), postrelease (PR), total CRM (CH + PR), and natural mortality (M) for small (≤103 cm CFL) and large (&gt;103 cm CFL) fish under different hypotheses and causes of mortality. CH was low (0%–8%) for both size classes but predation was an important component of PR, particularly in the small size class. Total CRM was 51% (95% CI: 26%, 81%) for small and 8% (95% CI: 2%, 30%) for large fish.

Remote Predictions of Mahi-Mahi (Coryphaena hippurus) Spawning in the Open Ocean Using Summarized Accelerometry Data

Identifying complex behaviors such as spawning and fine-scale activity is extremely challenging in highly migratory fish species and is becoming increasingly critical knowledge for fisheries management in a warming ocean. Habitat use and migratory pathways have been extensively studied in marine animals using pop-up satellite archival tags (PSATs), but high-frequency data collected on the reproductive and swimming behaviors of marine fishes has been limited by the inability to remotely transmit these large datasets. Here, we present the first application of remotely transmitted acceleration data to predict spawning and discover drivers of high activity in a wild and highly migratory pelagic fish, the mahi-mahi (Coryphaena hippurus). Spawning events were predicted to occur at nighttime, at a depth distinct from non-spawning periods, primarily between 27.5 and 30°C, and chiefly at the new moon phase in the lunar cycle. Moreover, throughout their large-scale migrations, mahi-mahi exhibited behavioral thermoregulation to remain largely between 27 and 28°C and reduced their relative activity at higher temperatures. These results show that unveiling fine-scale activity patterns are necessary to grasp the ecology of highly mobile species. Further, our study demonstrates that critical, and new, ecological information can be extracted from PSATs, greatly expanding their potential to study the reproductive behavior and population connectivity in highly migratory fishes.

Understanding the behavior and ecology of Chinook salmon (Oncorhynchus tshawytscha) on an important feeding ground in the Gulf of Alaska

Population declines and demographic changes of Chinook salmon (Oncorhynchus tshawytscha), have been documented throughout this species’ range, though information on natural and anthropogenic mechanisms related to these changes are not fully understood. To provide insights into marine behaviors and survival of Chinook salmon, 40 pop-up satellite archival tags (PSATs), that collected environmental data, were attached to large (69–100 cm FL) Chinook salmon caught in the marine waters of Cook Inlet, Alaska. PSATs provided evidence of predation on tagged Chinook salmon by ectothermic and unconfirmed predators, and provided valuable information about the migratory characteristics and occupied depths and temperatures of this species while occupying Cook Inlet and the Gulf of Alaska. The results from this study suggest that late-marine mortality of Chinook salmon of a variety of stock-origins by apex predators is more common in Cook Inlet than previously thought, and may be used to improve our understanding this species’ population dynamics. Furthermore, results from this study adds to the existing knowledge of marine habitat use by Chinook Salmon and may be useful in assessing the vulnerability and interactions between this species and anthropogenic activities.

Bigeye thresher shark Alopias superciliosus movements and post-release survivorship following capture on linked buoy gear

Off the US west coast, fishery development efforts have led to the recent recommendation for authorization of deep-set buoy gear (DSBG) and linked buoy gear (LBG), two commercial gear types for targeting swordfish at depth during the day. Because the new deep-set configurations interact with bigeye thresher sharks (Alopias superciliosus), a large pelagic species that is not typically retained for sale, this work has focused on documenting the fate of released catch. Bigeye thresher sharks (BETS) were captured and outfitted with pop-up satellite archival tags (Wildlife Computers sPATs and miniPATs) to assess movement trends and acute (30-d) post-release survival during exempted fishing trials authorized by National Marine Fisheries Service (NMFS) and the Pacific Fisheries Management Council (PFMC). Post-release survivorship was based on 14 BETS (∼157−230 cm LF) caught on LBG between August 2016 and December 2019 following fight times ranging from 17−300 min. Thirteen BETS survived the acute effects of capture, and one immediate mortality was documented following heavy entanglement in the monofilament leader. BETS were resilient to the acute effects of handling stress following capture on LBG, with an observed post-release survival rate of 93 %. Surviving BETS exhibited consistent diurnal dive patterns with sharks remaining well below the thermocline during the daytime (mean = 386 ± 62 m) and within the mixed layer at night (mean = 65 ± 25 m). With the exception of one tag that reported within close proximity of the SCB tagging location, BETS exhibited extensive southward movements (mean = 1235 ± 235 km) towards a potentially relevant migratory corridor for large pelagic sharks.

Water column structure defines vertical habitat of twelve pelagic predators in the South Atlantic

Abstract Quantifying vertical distributions of pelagic predators elucidates pelagic ecosystem structure and informs fisheries management. In the tropical South Atlantic Ocean, the recently designated large-scale marine protected area around Ascension Island hosts diverse pelagic predators for which basin-specific vertical habitat information is minimal or absent. We used pop-up satellite archival tags to analyse vertical habitat use in 12 species (bigeye tuna Thunnus obesus, blue marlin Makaira nigricans, blue shark Prionace glauca, dolphinfish Coryphaena hippurus, Galapagos shark Carcharhinus galapagensis, oceanic whitetip Carcharhinus longimanus, sailfish Istiophorus albicans, silky shark Carcharhinus falciformis, swordfish Xiphias gladius, tiger shark Galeocerdo cuvier, wahoo Acanthocybium solandri, and yellowfin tuna Thunnus albacares) and quantify parameters (temperature, dissolved oxygen, diel cycles, lunar phase) known to constrain vertical movements. Predator depth distributions varied widely, and classification trees grouped predators into four clades: (i) primarily epipelagic; (ii) partial thermocline use; (iii) oscillatory diving with thermocline/sub-thermocline use; and (iv) extensive use of sub-thermocline waters. Vertical habitat differences were linked to thermal physiology and foraging ecology, and species-specific physical constraints from other ocean basins were largely conserved in the South Atlantic. Water column features defined species-specific depth distributions, which can inform fisheries practices and bycatch risk assessments and population estimates.

Vertical and horizontal movements of bigeye tuna (Thunnus obesus) in southeastern Taiwan

ABSTRACT To learn about the movement patterns of bigeye tuna in eastern Taiwan, pop-up satellite archival tags were attached on five tuna ~55 kg and prematurely detached and popped-up after 32 to 132 days-at-liberty. Two tags were physically recovered and provided fine-scale data archiving the full 47 and 132 days-at-liberty. The deepest descent recorded was 1,292 m and the coldest temperature visited 2.7°C. During daytime, the fish spent the majority of time above 400 m at temperatures from ~10 - 25°C and at nighttime; residency was largely confined to the mixed-layer from the surface to ~100 m. Vertical movements traversing through the thermocline during the daytime are based on physiological constraints and/or rapid directional changes conducive for optimal search strategies that increases the chances of prey encounters. Bigeye tuna appear to follow the diel vertical movements of prey organisms comprising the deep sound scattering layer to exploit them as a resource.

Quantifying the effects of pop-up satellite archival tags on the swimming performance and behavior of young-adult mahi-mahi (Coryphaena hippurus)

Pop-up satellite archival tags (PSATs) have been used to demonstrate habitat utilization and large-scale migrations of aquatic species and are a critical tool to manage highly migratory fish populations. Use of PSATs has increased in recent years; however, few studies have investigated the physiological and behavioral effects of carrying a PSAT. To address this gap, young-adult mahi-mahi (Coryphaena hippurus; 25–35 cm fork length) were tagged with miniature PSATs and assessed in a two-part experiment utilizing swim tunnel respirometry and behavioral analysis of free-swimming individuals. Swim tunnel respirometry revealed significant reductions in the critical and optimal swimming speeds of tagged fish (10.2% and 20.9%, respectively), as well as significant reductions in maximum metabolic rate and aerobic scope (16.1% and 21.4%, respectively). In contrast, mean and maximum velocity, acceleration, total distance traveled, survival, and feeding success of free-swimming tagged fish showed no impacts of tagging compared with untagged conspecifics held in the same tank. The results of this study highlight the importance of considering multiple methodologies to assess the impacts of tagging fish and provide insight into the data collected by PSATs deployed on wild fish.

Habitat use and movement patterns of tiger sharks (Galeocerdo cuvier) in eastern Australian waters

Abstract Understanding the movement of marine predators is vital for effective conservation and management. Despite being targeted by shark control programs, the tiger shark, Galeocerdo cuvier, is poorly studied off eastern Australia. To investigate the horizontal movement and habitat use in this region, 16 sharks (157–384 cm total length) were tagged with MiniPAT pop-up satellite archival tags in 2018 and 2019. Eleven of these individuals were also fitted with satellite-linked radio transmitting tags. After release, most sharks moved off the continental shelf and headed north, associating with seamounts as they moved towards Queensland. During their time at liberty they transited through temperate, sub-tropical and tropical waters and spent the majority of time in the upper 50 m of the water column and at temperatures between 22 and 25˚C. Horizontal movement was focused in waters off the continental shelf. Increased movement over shelf waters occurred during the austral spring and summer when the East Australian Current is at its strongest and warm waters encroach the continental shelf. Broad latitudinal movement along the east coast of Australia was evident and highlights the connectivity between tropical and warm-temperate regions.

Seasonal migrations of pregnant blue sharks Prionace glauca in the northwestern Pacific

Information on the movements of highly migratory species is important to understand their ecology, including habitat use, population connectivity, and stock structure, to implement appropriate management and conservation measures. The blue shark Prionace glauca (Carcharhinidae) is highly migratory, has a global distribution, and is ecologically and economically important as one of the most abundant apex marine predators; however, the migration patterns of pregnant females are unknown. Here, we used pop-up satellite archival tags to elucidate seasonal migration of pregnant blue sharks in the northwestern Pacific. Of 24 tagged adult females, archival data were subsequently obtained for 21 individuals (141.1-243.3 cm precaudal length). Based on ultrasonography or analysis of sex steroid hormones, 17 of these females were confirmed to be pregnant at the time of release. Females with small embryos moved in a northeasterly direction, from subtropical (10-30°N) into temperate (30-40°N) waters during autumn and the following spring; 2 of these females returned to subtropical waters in spring and summer. In contrast, females with large embryos moved in a southwesterly direction, from temperate into subtropical waters during spring and autumn. Tagged sharks also showed regional differences in diving behaviors, reflecting thermal habitats in the ocean environment. Our findings indicate that pregnant blue sharks undergo a seasonal northeast-southwest migration within a year to give birth to pups in productive temperate waters. This is the first report on seasonal reproductive migration of pregnant blue sharks in the global ocean.

Novel use of pop-up satellite archival telemetry in sawsharks: insights into the movement of the common sawshark Pristiophorus cirratus (Pristiophoridae)

BackgroundUnderstanding movement patterns of a species is vital for optimising conservation and management strategies. This information is often difficult to obtain in the marine realm for species that regularly occur at depth. The common sawshark (Pristiophorus cirratus) is a small, benthic-associated elasmobranch species that occurs from shallow to deep-sea environments. No information is known regarding its movement ecology. Despite this, P. cirrata are still regularly landed as nontargeted catch in the south eastern Australian fisheries. Three individuals were tagged with pop-up satellite archival tags (PSATs) off the coast of Tasmania, Australia, to test the viability of satellite tagging on these small elasmobranchs and to provide novel insights into their movement.ResultsTags were successfully retained for up to 3 weeks, but movement differed on an individual basis. All three individuals displayed a post-release response to tagging and limited vertical movement was observed for up to 5–7 days post-tagging. Temperature loggers on the tags suggest the animals were not stationary but moved horizontally during this time, presumably in a flight response. After this response, continuous wavelet transformations identified diel vertical movements in one individual at cyclical intervals of 12- and 24-hour periods; however, two others did not display as clear a pattern. Temperature was not significantly correlated with movement in the study period. The deepest depths recorded during the deployments for all individuals was approximately 120 m and the shallowest was 5 m.ConclusionsThis study demonstrates that sawsharks can be successfully tagged by pop-up satellite archival tags. The data presented here show that sawsharks regularly move both horizontally and vertically in the water column, which was an unexpected result for this small benthic species. Additional research aimed at resolving the trophic ecology will help identify the drivers of these movements and help to better define the ecological, behavioural and physiological roles of these sharks in their ecosystems. These data describe a substantial ability to move in the common sawshark that was previously unknown and provides the first account of movement ecology on the family of sawsharks: Pristiophoridae.

Post-release survival of silky sharks (Carcharhinus falciformis) following capture by Mexican flag longline fishing vessels in the northeastern Pacific Ocean

Mexican flag longline fishing vessels operating in tropical waters of the northeastern Pacific Ocean commonly target and land silky sharks (Carcharhinus falciformis). In this study silky sharks captured by Mexican flag longline fishing vessels in the northeastern Pacific Ocean and brought onboard were tagged and released with pop-up satellite archival tags (PSATs), following removal of hooks or cutting gangions as close to the hook as feasible, to evaluate their post-release survival (PRS). The PRS rate estimated using Kaplan - Meier survival analyses was 84.8 % (95 % CI: 71.0 %–100 %) for 63 silky sharks. Utilizing a rope noose to lift sharks aboard vessels was demonstrated to be an effective handling method. The 58 silky shark survivors were at liberty with PSATs attached for an average of 102 days (range: 1–298 d). Average linear displacement for 46 silky sharks at liberty for > 30 d was 512 nmi (range: 45–927 nmi), indicating relatively rapid widespread dispersion from release locations.

Stock-scale electronic tracking of Atlantic halibut reveals summer site fidelity and winter mixing on common spawning grounds

Abstract Knowledge of movement ecology, habitat use, and spatiotemporal distribution is critical to inform sustainable fisheries management and conservation. Atlantic halibut in the Gulf of St. Lawrence (GSL) is of great economic value, although little is known about its spatiotemporal distribution, seasonal migrations, and spawning areas. To investigate these aspects, 114 pop-up satellite archival tags (PSATs) were deployed on halibut from 2013 up to 2018 throughout the GSL. A total of 62 physically recovered PSATs provided complete archived datasets with high temporal resolution. PSAT detachment locations revealed specific summer site fidelity. In contrast, the reconstruction of movement tracks with a geolocation model revealed that all fish converged to the Gulf’s deep channels to overwinter and spawn. This suggests strong mixing during the spawning period and thus one reproductive population within the GSL. These findings illustrate the utility of large-scale PSAT tagging combined with dedicated PSAT-recovery surveys to reveal critical stock-scale information on movements and spawning locations. This information addresses important gaps in the movement ecology of this halibut stock, revealing that reported summer site fidelity, based on years of conventional tagging, also conceals important winter mixing that is only apparent through analyses of movement on the time scale of annual cycles.

First insights into the vertical habitat use of the whitespotted eagle ray Aetobatus narinari revealed by pop-up satellite archival tags.

The whitespotted eagle ray Aetobatus narinari is a tropical to warm-temperate benthopelagic batoid that ranges widely throughout the western Atlantic Ocean. Despite conservation concerns for the species, its vertical habitat use and diving behaviour remain unknown. Patterns and drivers in the depth distribution of A. narinari were investigated at two separate locations, the western North Atlantic (Islands of Bermuda) and the eastern Gulf of Mexico (Sarasota, Florida, U.S.A.). Between 2010 and 2014, seven pop-up satellite archival tags were attached to A. narinari using three methods: a through-tail suture, an external tail-band and through-wing attachment. Retention time ranged from 0 to 180 days, with tags attached via the through-tail method retained longest. Tagged rays spent the majority of time (82.85 ± 12.17% S.D.) within the upper 10 m of the water column and, with one exception, no rays travelled deeper than ~26 m. One Bermuda ray recorded a maximum depth of 50.5 m, suggesting that these animals make excursions off the fore-reef slope of the Bermuda Platform. Individuals occupied deeper depths (7.42 ± 3.99 m S.D.) during the day versus night (4.90 ± 2.89 m S.D.), which may be explained by foraging and/or predator avoidance. Each individual experienced a significant difference in depth and temperature distributions over the diel cycle. There was evidence that mean hourly depth was best described by location and individual variation using a generalized additive mixed model approach. This is the first study to compare depth distributions of A. narinari from different locations and describe the thermal habitat for this species. Our study highlights the importance of region in describing A. narinari depth use, which may be relevant when developing management plans, whilst demonstrating that diel patterns appear to hold across individuals.