Pop-up Satellite Archival Transmitters Research Articles

Spatial Dynamics and Fine-Scale Vertical Behaviour of Immature Eastern Australasian White Sharks (Carcharodon carcharias).

Knowledge of the 3-dimensional space use of large marine predators is central to our understanding of ecosystem dynamics and for the development of management recommendations. Horizontal movements of white sharks, Carcharodon carcharias, in eastern Australian and New Zealand waters have been relatively well studied, yet vertical habitat use is less well understood. We dual-tagged 27 immature white sharks with Pop-Up Satellite Archival Transmitting (PSAT) and acoustic tags in New South Wales coastal shelf waters. In addition, 19 of these individuals were also fitted with Smart Position or Temperature Transmitting (SPOT) tags. PSATs of 12 sharks provided useable data; four tags were recovered, providing highly detailed archival data recorded at 3-s intervals. Horizontal movements ranged from southern Queensland to southern Tasmania and New Zealand. Sharks made extensive use of the water column (0-632 m) and experienced a broad range of temperatures (7.8-28.9 °C). Archival records revealed pronounced diel-patterns in distinct fine-scale oscillatory behaviour, with sharks occupying relatively constant depths during the day and exhibiting pronounced yo-yo diving behaviour (vertical zig-zag swimming through the water column) during the night. Our findings provide valuable new insights into the 3-dimensional space use of Eastern Australasian (EA) white sharks and contribute to the growing body on the general ecology of immature white sharks.

Spawning migration and larval dispersal of tropical Pacific eels (Anguilla spp.) in the centre of their distribution ranges

It is unknown how many spawning areas exist for tropical South Pacific eels (Anguilla marmorata, A. megastoma, A. obscura) populating island archipelagos between Papua New Guinea and French Polynesia. They could spawn at single centralised eastern and western locations, implying long-distance migrations by some eels, or at several local spawning areas. Larval catches, morphological and genetic investigations, and tagging experiments have provided no unequivocal answer. In this study, A. marmorata and A. megastoma were tagged with pop-up satellite archival transmitters at Samoa, in the centre of their distribution ranges. Tags surfaced prematurely after 11 to 25 d, 91 to 345 km from the point of release. One A. marmorata and one A. megastoma came within 180 and 230 km, respectively, from where a small A. marmorata leptocephalus was caught north of American Samoa during a recent research cruise, suggesting that eels may spawn near the archipelago. Silver eels exhibited diel vertical migrations between 180 m during the night and more than 700 m during the day. At their upper migration depths, eels migrated towards increasing salinity and towards local eddies, raising the question of whether they may actively search for these oceanographic features. Up to 15% of virtual larvae released near Samoa were retained within local eddies and could have recruited back to the archipelago. The remaining larvae drifted as far as Fiji and the Cook Islands to the west and east, respectively. The exchange of leptocephali probably connects several local spawning areas throughout the South Pacific Ocean, causing genetic exchange among areas.

Fine-scale vertical habitat use of white sharks at an emerging aggregation site and implications for public safety

Abstract 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.

Vertical movements of a pelagic thresher shark (Alopias pelagicus): insights into the species’ physiological limitations and trophic ecology in the Red Sea

The pelagic thresher shark Alopias pelagicus is an understudied elasmobranch harvested in commercial fisheries of the tropical Indo-Pacific. The species is endangered, overexploited throughout much of its range, and has a decreasing population trend. Relatively little is known about its movement ecology, precluding an informed recovery strategy. Here, we report the first results from an individual pelagic thresher shark outfitted with a pop-up satellite archival transmitting (PSAT) tag to assess its movement with respect to the species’ physiology and trophic ecology. A 19 d deployment in the Red Sea revealed that the shark conducted normal diel vertical migration, spending the majority of the day at 200-300 m in the mesopelagic zone and the majority of the night at 50-150 m in the epipelagic zone, with the extent of these movements seemingly not constrained by temperature. In contrast, the depth distribution of the shark relative to the vertical distribution of oxygen suggested that it was avoiding hypoxic conditions below 300 m even though that is where the daytime peak of acoustic backscattering occurs in the Red Sea. Telemetry data also indicated crepuscular and daytime overlap of the shark’s vertical habitat use with distinct scattering layers of small mesopelagic fishes and nighttime overlap with nearly all mesopelagic organisms in the Red Sea as these similarly undergo nightly ascents into epipelagic waters. We identify potential depths and diel periods in which pelagic thresher sharks may be most susceptible to fishery interactions, but more expansive research efforts are needed to inform effective management.

Tracking the marine migration routes of South Pacific silver eels.

Three catadromous Pacific eels (2 Anguilla marmorata, 1 A. megastoma) from the Archipelago of Vanuatu were tagged with pop-up satellite archival transmitters and their migration tracks towards their presumed spawning area approximately 870 km northeast of the point of release were reconstructed in order to evaluate their movements in relation to oceanographic conditions. We used the timing of diel vertical migrations to derive the eels' positions. Two A. marmorata exhibited steep-angled turns resulting in a zig-zag migration path along the east-west axis, while one A. megastoma took a relatively straight course towards the presumed spawning area. They migrated with a speed over ground of 21-23 km day-1. In this region, the eastward flow of the South Equatorial Counter Current (SECC, ∼ 5-10°S) separates the westward flowing South Equatorial Current (SEC; ∼0-5°S and 10-18°S) into two branches. During shallower nighttime migration depths around 150 m eels crossed a variable flow field through the southern branch of the westward SEC with westward propagating mesoscale eddies and the eastward SECC, but stayed south of the stronger northern branch of SEC possibly increasing retention time of larvae within this area. The eels headed towards a tongue of high-salinity Subtropical Underwater (STUW) that may have provided cues for orientation. The eels did not move beyond a salinity front of 35.9-36.0 at a depth of 100-200 m, which may have provided cues for orientation towards the spawning area. These 3 tracks may represent the movements of mature silver eels all the way to where they spawn.

Capture stress and post-release mortality of blacktip sharks in recreational charter fisheries of the Gulf of Mexico.

Understanding the stress responses of sharks to recreational catch and release fishing has important management and conservation implications. The blacktip shark Carcharhinus limbatus is a popular recreational species targeted throughout the western, central and eastern Gulf of Mexico (Gulf) yet it is unclear what levels of physiological stress result from catch-release fishing practices with hook and line gear and if the stress levels result in post-release mortality. This study correlates physiological response to stress through blood chemistry analysis and examines post-release behaviour of adult blacktip sharks caught to determine post-release mortality rates. Release behaviour was determined by pop-up satellite archival transmitting (PSAT) tags that record temperature, depth and light level data. To quantify physiological stress levels, blood samples were collected from 52 blacktip sharks and a suite of metabolic and osmotic markers were measured. Thirty-six of those blacktip sharks were also outfitted with a PSAT tag yielding time-at-large from 3 to 180days. Of the 36 tags, 22 (61%) provided sufficient data to confirm post-release fate and 11 (31%) were recovered providing high-resolution data. Tag data suggests a post-release morality rate of 22.7% (95% confidence interval 7.8-45.4%), with mortality occurring within minutes (immediate mortality) to over 12h post-release (delayed mortality). Compared to survivors, immediate mortalities exhibited significantly higher lactate (median 2.8mmol/Lsurvivor vs 5.9mmol/Limmediate mortality) and significantly lower hematocrit (median 24.4% survivor vs 14% immediate mortality) levels, but no difference was detected between survivors and delayed mortalities. Higher mortality in the western (30%) compared to the central (20%) Gulf may be due to shark handling. All PSATs from mortalities (N = 5) were recovered, and archived data revealed evidence of tag ingestion by predators. Results suggest reduced fight time, decreased handling time and limited air exposure provide blacktip sharks the best survival chances after release by recreational anglers.

Utilization of pop-up satellite archival transmitting tags to evaluate thorny skate (Amblyraja radiata) discard mortality in the Gulf of Maine groundfish bottom trawl fishery

Abstract 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 <1% of the existing stock biomass in the GOM (8400 mt). This study confirms that thorny skate are relatively resilient to bottom trawl fishing practices in the GOM, and suggests that other sources of mortality may be impeding population recovery.

Observing post-release mortality for dusky sharks, Carcharhinus obscurus, captured in the U.S. pelagic longline fishery

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.

Post-release survivorship and movements of bigeye thresher sharks, Alopias superciliosus, following capture on deep-set buoy gear

The bigeye thresher shark (Alopias superciliosus) is a large pelagic predator routinely caught in a new deep-set fishery off California. Deep-set buoy gear (DSBG) was recently developed to selectively target swordfish (Xiphias gladius) at depth during the daytime and is currently being trialed by a limited fleet of vessels operating under an exempted fishing permit (EFP) issued through the National Marine Fishery Service (NMFS) and Pacific Fisheries Management Council (PFMC). Although marketable, bigeye thresher sharks (BETS) are often released or discarded to conserve limited hold space for more valuable catch. This study outfitted BETS with pop-up satellite archival transmitters (PSATs) programmed for 30-day deployments to evaluate acute post-release survival in the DSBG fishery and begin to understand depth and temperature distribution for this poorly known species. Fourteen BETS (43–93 kg) were tagged from 2016 to 2018 with PSATs (Wildlife Computers sPATs and MiniPATs) following fight times that ranged from 15 to 171 min. Out of the 14 deployments, twelve individuals survived the acute effects of capture, one BETS died shortly after release and one individual was preyed upon 6 h after release. Given the lack of information surrounding the predation induced mortality, two survivorship estimates are provided, one that includes the event as a mortality resultant of the capture event (86% survivorship) and one that excludes the event from the analysis (92% survivorship). All surviving BETS exhibited consistent diurnal dive patterns in which the sharks remained below the thermocline during the day and within the mixed layer at night. Mean daytime depths ranged from 250 to 439 m, while mean nighttime depths ranged from 20 to 106 m. Daytime temperatures at depth ranged from 6 to 10 °C with the lowest temperature value (6.0 °C) recorded on the deepest dive (548 m). For all BETS, maximum night temperatures averaged from 22.5 to 25.1 °C. Two tagged individuals remained proximal to the study area (<150 km) with others moving up to >1300 km from the tagging site (mean = 1009 ± 455 km). Mean daily rates of horizontal movement ranged from 3.4 to 41.6 km day−1. The most common movement trend entailed BETS moving in a southerly direction towards a series of offshore seamounts along southern Baja California, Mexico (22°-26 °N and 114°-126 °W), a purported offshore corridor for other large pelagic sharks of the eastern Pacific.

Assimilating electronic tagging, oceanographic modelling, and fisheries data to estimate movements and connectivity of swordfish in the North Atlantic

Abstract Broadbill swordfish (Xiphias gladius) is a key species in commercial fisheries, but management efforts continue to be hindered by data gaps in their basic biology, including ongoing debate over stock boundaries and movement between management zones. We deployed 20 pop-up satellite archival transmitting (PSAT) tags on juvenile swordfish in the Azores and adults in the northwest Atlantic (NWA). We applied a recently developed geolocation approach that synthesizes tag data with a global observation-assimilating ocean model to improve geolocation accuracy. Resulting tracks from 16 individuals averaged 3751 km (range 345–7247 km) over 93 days (range 17–181 days). Juveniles tagged in the Azores made regional movements while adults tagged in the NWA moved between summer foraging grounds near the Grand Banks to winter habitats near the Antillean Arc. All individuals spent considerable time in the mesopelagic zone during the day, and this behaviour increased with fish size. We integrate results from our PSAT-based movements with conventional tag and catch-per-unit effort data, which indicates complex stock structure within the North Atlantic that largely supports current stock boundaries. Our work demonstrates the utility in synthesizing fishery-independent electronic tag data and fisheries datasets to improve our understanding of large pelagic fish ecology.

Biotelemetry based estimates of greater amberjack (Seriola dumerili) post-release mortality in the northern Gulf of Mexico

The Gulf of Mexico greater amberjack (Seriola dumerili) stock has been designated as “overfished” by the National Marine Fisheries Service and is currently under a rebuilding plan. Its fishery in the Gulf of Mexico is dominated by recreational landings, where 75% of the total recreational catch are regulatory discards; as such, uncertainty regarding the post-release mortality rate represents a data deficiency in the stock assessment. To determine post-release mortality, a combination of acoustic and pop-up satellite archival transmitting (PSAT) tags were used to monitor the release fate and depth-use of greater amberjack. Thirty-six greater amberjack were tagged with acoustic transmitters at two sites in the northern GOM and monitored for up to 30 days. Sublegal-sized fish (n = 18) ranged from 591 to 740 mm FL (mean = 674.6 ± 40.6 SE) and legal-sized fish (n = 18) ranged from 768 to 1081 mm FL (mean = 871.3 ± 77.5 SE). All 36 fish were detected in the array after release. Based on examination of time series depth profiles, post-release mortality was estimated to be 18.8% ± 6.9%, strikingly similar to the estimate used in the most recent stock assessment. Stepwise model selection using AIC identified the Cox proportional hazards model containing only release condition as the most parsimonious model to predict post-release mortality. Despite differences in depth between the two tagging sites, fish showed slight, but consistent, size-specific segregation patterns. Our findingsadd to a body of literature demonstrating that biotelemetry is an effective tool in catch and release mortality studies, and provide best practices that can aid in the recovery of this stock.

Integrating Archival Tag Data and a High-Resolution Oceanographic Model to Estimate Basking Shark (Cetorhinus maximus) Movements in the Western Atlantic

Basking shark (Cetorhinus maximus) populations are considered ‘vulnerable’ globally and ‘endangered’ in the northeast Atlantic by the International Union for the Conservation of Nature. Much of our knowledge of this species comes from surface observations in coastal waters, yet recent evidence suggests the majority of their lives may be spent in the deep ocean. Depth preferences of basking sharks have significantly limited movement studies that used pop-up satellite archival transmitting (PSAT) tags as conventional light-based geolocation is impossible for tagged animals that spend significant time below the photic zone. We tagged 57 basking sharks with PSAT tags in the NW Atlantic from 2004-2011. Many individuals spent several months at meso- and bathy-pelagic depths where accurate light-level geolocation was impossible during fall, winter and spring. We applied a newly-developed geolocation approach for the PSAT data by comparing three-dimensional depth-temperature profile data recorded by the tags to modeled in-situ oceanographic data from the high-resolution HYbrid Coordinate Ocean Model (HYCOM). Observation-based likelihoods were leveraged within a state-space hidden Markov model (HMM). The combined tracks revealed that basking sharks moved from waters around Cape Cod, MA to as far as the SE coast of Brazil (20°S), a total distance of over 17,000km. Moreover, 59% of tagged individuals with sufficient deployment durations (> 250 days) demonstrated seasonal fidelity to Cape Cod and the Gulf of Maine, with one individual returning to within 60 km of its tagging location one year later. Tagged sharks spent most of their time at epipelagic depths during summer months around Cape Cod and in the Gulf of Maine. During winter months, sharks spent extended periods at depths of at least 600 m while moving south to the Sargasso Sea, the Caribbean Sea, or the western tropical Atlantic. Our work demonstrates the utility of applying advances in oceanographic modeling to understanding habitat use of highly migratory, often meso- and bathy-pelagic, ocean megafauna. The large-scale movement patterns of tagged sharks highlight the need for international cooperation when designing and implementing conservation strategies to ensure that the species recovers from the historical effects of over-fishing throughout the North Atlantic Ocean.

Horizontal and vertical movements of white marlin, Kajikia albida, tagged off the Yucatán Peninsula

Abstract The white marlin, Kajikia albida, is a highly migratory, prized sport fish of conservation concern. Improved understanding of white marlin ecology, including habitat use, will inform management measures. To improve white marlin movement knowledge in a region with limited information, we tagged 18 individuals off the eastern Yucatan Peninsula, Mexico with pop-up satellite archival transmitters. Tracks lasting 9–328 d, yielded data across 1277 d, and covered distances of 891–10 579 km. Horizontal movements varied greatly with ten individuals remaining in the Gulf of Mexico/northwestern Caribbean and eight individuals entering the western North Atlantic. Although white marlin experienced a temperature range of 10.0–33.6 °C, the majority of time was spent in waters &amp;gt;24 °C. Marlin displayed diel diving patterns with deeper dives occurring more frequently during the daytime. As water columns warmed, dive duration, maximum daily depth, and dive depth all increased. As a result, 18% of the time was spent at depths &amp;gt;100 m in the warmest water columns compared with &amp;lt;1% in the coldest water columns. Although the thermal characteristics of the water column greatly influence white marlin diving behaviour, the generally shallow distributions provide a way of separating white marlin from important fishery species.

Environmental influence on the seasonal movements of satellite-tracked ocean sunfish Mola mola in the north-east Atlantic

Determining the habitat use of mobile marine species is important for understanding responses to climate change and aids the implementation of management and conservation measures. Inference of preferred habitat use has been greatly improved by combining satellite-based oceanographic data with animal tracking techniques. Although there have been several satellite-tracking studies on ocean sunfish Mola mola, limited information is available about either horizontal or vertical environmental preferences. In this study, both geographical movements and diving behaviour of ocean sunfish were explored together with the environmental factors influencing this species’ space use in the north-east Atlantic. Habitat selection of electronic-tagged sunfish (n = 22 individuals; 0.6–1.4 m total length, TL) was investigated using geolocations from Argos-linked and pop-up satellite archival transmitters. Satellite tracking (up to 171 days, mean 66 days) revealed seasonal movements: northward in spring–summer and southward in cooler months. Sunfish spent extended periods in three focal areas, the Gulf of Cadiz, north-east Iberia and the Alboran gyre, which are characterised by the presence of frontal features with elevated primary production. Habitat modelling revealed that sea surface temperature and thermal gradients significantly influenced sunfish distribution. Diving profiles, extending from the surface to a maximum depth of 704 m, revealed different depth-use patterns not linked to geographical region or water column stratification. Overall, a size-related movement pattern was detected with larger individuals (>0.92 m TL) travelling further, exploiting greater depth ranges and spending more time at depth than smaller fish. Ocean sunfish in the north-east Atlantic displayed seasonal movements, primarily driven by thermal preferences, extending into higher latitudes in summer. Moreover, fish also occupied productive frontal areas for long periods, presumably for improved foraging opportunities. Lastly, sunfish showed considerable variability in diving patterns which likely reflect the tracking of planktonic prey distributions.

Movements of the reef manta ray (Manta alfredi) in the Red Sea using satellite and acoustic telemetry

Populations of mobulid rays are declining globally through a combination of directed fisheries and indirect anthropogenic threats. Understanding the movement ecology of these rays remains an important priority for devising appropriate conservation measures throughout the world’s oceans. We sought to determine manta movements across several temporal and spatial scales with a focus on quantifying site fidelity and seasonality in the northern Farasan Banks, Red Sea. We fitted manta rays with acoustic transmitters (n = 9) and pop-up satellite archival transmitting (PSAT) tags (n = 9), including four with GPS capability (Fastloc), during spring 2011 and 2012. We deployed an extensive array of acoustic receivers (n = 67) to record movements of tagged mantas in the study area. All acoustically tagged individuals traveled frequently among high-use receiver locations and reefs and demonstrated fidelity to specific sites within the array. Estimated and realized satellite tag data indicated regional movements <200 km from the tagging location, largely coastal residency, and high surface occupation. GPS-tagged individuals regularly moved within the coastal reef matrix up to ~70 km to the south but continued to return to the tagging area near the high-occupancy sites identified in the acoustic array. We also tested the accuracy of several geolocation models to determine the best approach to analyze our light-based satellite tag data. We documented significant errors in light-based movement estimates that should be considered when interpreting tracks derived from light-level geolocation, especially for animals with restricted movements through a homogenous temperature field. Despite some error in satellite tag positions, combining results from PSAT and acoustic tags in this study yielded a comprehensive representation of manta spatial ecology across several scales, and such approaches will, in the future, inform the design of appropriate management strategies for manta rays in the Red Sea and tropical regions worldwide.

Satellite telemetry reveals physical processes driving billfish behavior

Pop-up satellite archival transmitting (PSAT) tags are capable of storing high-resolution behavioral and environmental information for extended periods of time (approximately 1 year), rendering them especially valuable for studying highly mobile species. In this review, we synthesize published PSAT data to understand the biophysical drivers that influence movements of billfishes (families Xiphiidae and Istiophoridae). To date, over 1,080 PSATs have been deployed on billfishes, with individuals demonstrating both trans-equatorial and trans-basin movements. Using this dataset, we identify four main physical variables that drive billfish behavior: temperature, light, oxygen, and complex water mixing (e.g. fronts and eddies). Of the seven species that have been studied with PSAT technology, all exhibited a strong thermal preference for water >22°C, though vertically migrating swordfish additionally occupied waters <10°C while at depth. Ambient light levels influence vertical movements, especially those associated with foraging, as billfish possess large eyes and thermoregulatory abilities that facilitate feeding behaviors below warm surface layers. Mounting evidence suggests that some billfishes actively avoid regions with low dissolved oxygen (<3.5 mL L−1). Human-induced climate change is expected to increase the horizontal and vertical extent of hypoxic water and may further compress habitat and concentrate fishing pressure on pelagic fishes. Finally, complex submeso- and mesoscale processes provide critical habitat for spawning, larval feeding, and retention, but our understanding of these and other behavioral aspects of billfish biology remains limited. Future research efforts should leverage technical advancements while integrating existing and future tag data with chemical and physical oceanographic datasets to gain a better understanding of the relevant biophysical interactions for billfishes, thereby enhancing management capabilities for this ecologically and economically important group of fishes.

Diel vertical movements of adult male dolphinfish (Coryphaena hippurus) in the western central Atlantic as determined by use of pop-up satellite archival transmitters

The vertical movements of six adult male dolphinfish (Coryphaena hippurus) (95–120 cm estimated fork length), caught using standard sportfishing methods, were investigated using high-rate single-point pop-up satellite archival transmitters from 2005 to 2011 in the western central Atlantic. Data revealed a diel activity pattern within the mixed surface layer with dives below the thermocline suggesting temperature is not a barrier to vertical movements for short periods of time. Dolphinfish were tracked for periods of 4.96–30.24 day (Σ = 83.37 day), reaching depths >200 m, and in temperatures ranging from 16.20 to 30.87 °C. The six tags allowed comprehensive vertical movement analyses by time of day, duration at depth, and based on vertical movement patterns. The longest (>60 min), deepest (>30 m), and most extensive vertical movement patterns occurred during night rather than day, with the most time spent near the surface during the day. Dolphinfish spent 66 % of their time in the surface layer (0–9.9 m) and only one individual spent 8 % of the monitoring period diving >8 °C from the maximum surface temperatures recorded while tracked. Two tags were analyzed based on lunar phase and revealed contrasting relationships between vertical movements during new and full phases. Our results suggest dolphinfish vertically shift between surface and at-depth feeding strategies to exploit aggregating epipelagic and mesopelagic prey items leading to predictable diel vertical movements.

Development and testing of attachment methods for pop-up satellite archival transmitters in European eel

Four methods for attaching pop-up satellite transmitters to European eel were tested in the laboratory by recording long-term tag retention, growth and survival; short-term behavioral responses; and physical damage from attachments. All eels survived until they lost their tag, or until end of the six-month study. Specific growth rate did not differ between tagged fish and controls. Tag retention varied from 0% to 100% among attachment methods. A tagging method that uses the strength of the eel skin by attaching the tag to the skin at three points is recommended for ocean migration studies based on a long tag retention time, minimal behavioral reactions, negligible damage to the swimming muscle, and minimal physical damage both for fish retaining and losing the tag. Although tag retention was 50% over six months, those losing their tags still retained them for 114 to 134 days. Another method had higher tag retention (100%), but required the use of steel wires that moved upwards through the muscle over time. This method was regarded as less suitable because of a strong behavioral reaction in the first two days after tagging and damage to the swimming muscle. Results from 275 silver eels released on European coasts equipped with pop-up satellite transmitters or similarly sized pop-up data storage tags to study the ocean spawning migration indicated a large premature tag release. This was partly related to mechanical tag loss, but probably mainly to a high predation rate (>20% confirmed predations of eels with pop-up satellite transmitters). Mean time to premature tag release was 14 to 21 days (maximum nine months). Laboratory and field data showed that pop-up satellite transmitters attached to eels can remain attached for six to nine months, but that tag retention is a challenge. Hiding behavior in a structured habitat increased the risk of entanglement and tag loss. In ocean migration studies, consideration should be given to transportation and release off shore instead of in shallower areas where they are more likely to seek the seabed and hide in structured habitats. Behavioral reactions indicate that data recorded during the first two to three days after tagging may not reflect natural behavior.

Transequatorial Migrations by Basking Sharks in the Western Atlantic Ocean

The world's second largest fish, the basking shark (Cetorhinus maximus), is broadly distributed in boreal to warm temperate latitudes of the Atlantic and Pacific oceans from shallow coastal waters to the open ocean. Previous satellite archival tagging in the North Atlantic has shown that basking sharks move seasonally, are often associated with productive frontal zones, and may make occasional dives to mesopelagic depths. However, basking sharks are thought to be restricted to temperate latitudes, and the extent to which they exploit deeper-water habitat remains enigmatic. Via satellite archival tags and a novel geolocation technique, we demonstrate here that basking sharks are seasonal migrants to mesopelagic tropical waters. Tagged sharks moved from temperate feeding areas off the coast of southern New England to the Bahamas, the Caribbean Sea, and onward to the coast of South America and into the Southern Hemisphere. When in these areas, basking sharks descended to mesopelagic depths and in some cases remained there for weeks to months at a time. Our results demonstrate that tropical waters are not a barrier to migratory connectivity for basking shark populations and highlight the need for global conservation efforts throughout the species range.