Advancements in space-based ocean observation and computational data processing techniques have demonstrated transformative value for managing living resources, biodiversity, and ecosystems of the ocean. We synthesize advancements in leveraging satellite-derived insights to better understand and manage fishing, an emerging revolution of marine industrialization, ocean hazards, sea surface dynamics, benthic ecosystems, wildlife via electronic tracking, and direct observations of ocean megafauna. We consider how diverse space-based data sources can be better coupled to modernize and improve ocean management. We also highlight examples of how data from space can be developed into tools that can aid marine decision-makers managing subjects from whales to algae. Thoughtful and prospective engagement with such technologies from those inside and outside the marine remote sensing community is, however, essential to ensure that these tools meet their full potential to strengthen the effectiveness of ocean management.

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.

Vertical space use informs the ecology and management of marine species, but studies of reef-associated sharks often focus on horizontal movements. We analysed the vertical movements of silvertip sharks Carcharhinus albimarginatus using pop-up archival tags deployed on 7 individuals in the Chagos Archipelago, central Indian Ocean. The sharks changed depth predictably with water column thermal structure, moving deeper with seasonal increases in mixed layer depth while occupying a narrow ambient water temperature range around ~27°C. At shorter timescales, higher resolution data from 5 tags showed that silvertip shark depth varied cyclically with surface light levels, increasing during daylight and on nights around the full moon. This matches the diel vertical migrations of many fish species, suggesting that the sharks’ light-driven depth changes might relate to foraging. While most vertical movements (>98%) were within the mixed layer, deeper dives to 200-800 m occurred approximately every 3 d. High-resolution data from one recovered tag showed the shark ascending deep (>200 m) dives in 2 sharply defined phases, initially fast then slow. Analysis of dive profiles against dissolved oxygen (DO) data suggested that the shark may have ascended rapidly to escape low DO levels at depth, then reduced its ascent rate by 50-80% once DO levels increased. While a small sample, the electronic tags deployed in this study revealed the silvertip sharks’ predictable use of mixed layer waters, narrow thermal range and apparent intolerance of hypoxic conditions. These characteristics may exacerbate the species’ vulnerability as oceanic warming and shoaling oxygen minimum zones modify vertical habitat availability.

Tuna are known for exceptional swimming speeds, which are possible because of their thunniform lift-based propulsion, large muscle mass and rigid fusiform body. A rigid body should restrict maneuverability with regard to turn radius and turn rate. To test if turning maneuvers by the Pacific bluefin tuna (Thunnus orientalis) are constrained by rigidity, captive animals were videorecorded overhead as the animals routinely swam around a large circular tank or during feeding bouts. Turning performance was classified into three different types: (1) glide turns, where the tuna uses the caudal fin as a rudder; (2) powered turns, where the animal uses continuous near symmetrical strokes of the caudal fin through the turn; and (3) ratchet turns, where the overall global turn is completed by a series of small local turns by asymmetrical stokes of the caudal fin. Individual points of the rostrum, peduncle and tip of the caudal fin were tracked and analyzed. Frame-by-frame analysis showed that the ratchet turn had the fastest turn rate for all points with a maximum of 302 deg s-1. During the ratchet turn, the rostrum exhibited a minimum global 0.38 body length turn radius. The local turn radii were only 18.6% of the global ratchet turn. The minimum turn radii ranged from 0.4 to 1.7 body lengths. Compared with the performance of other swimmers, the increased flexion of the peduncle and tail and the mechanics of turning behaviors used by tuna overcomes any constraints to turning performance from the rigidity of the anterior body morphology.

Sustainable management of exploited marine fish and wildlife populations requires knowledge about their productivity. Survival from natural causes of mortality is a key component of population productivity, but is notoriously difficult to estimate. We evaluate the potential for acoustic telemetry as a long-term monitoring tool to estimate rates of natural mortality. We present a Bayesian multistate mark-recapture model for telemetry data collected over a decade from 188 Atlantic bluefin tuna ( Thunnus thynnus) and apply it to estimate the rate of natural mortality using only acoustic tag detections for all animals, or using acoustic tag detections for 96 single-tagged tuna plus acoustic tag detections combined with estimated positions from pop-up satellite archival tags for 92 double-tagged animals. We support the model for bluefin tuna with a simulation study to quantify bias in estimates of population dynamics parameters and investigate the effect of auxiliary information from satellite tagging on mortality rate estimates for different acoustic tag detection probability scenarios. We obtained posterior estimates of the instantaneous annual natural mortality (survival) rate across a decade of tagging for Atlantic bluefin tuna of 0.17 yr -1 (0.84 yr -1 ) both using only acoustic tagging data, and using a combination of acoustic and satellite tagging data. Use of a prior implying a higher rate of fishing mortality yielded an instantaneous annual natural mortality (survival) estimate of 0.10 yr -1 (0.90 yr -1 ), with combined acoustic and satellite tag data. Results from the simulation study indicate that the use of satellite tags can improve the precision and accuracy of estimates of detection probabilities, area-specific movement probabilities and mortality rates, where the extent of the improvement depends on true underlying acoustic tag detection probabilities. Our work demonstrates that long-term acoustic tagging data sets have strong potential for monitoring of highly migratory marine fish and wildlife populations, providing information on a number of key parameters, including survival and movement rates. However, improved information on tag reporting rates or fishing mortality is needed to better separate natural and fisheries mortality for Atlantic bluefin tuna.

Aim Climate change is driving the redistribution of species throughout the oceans. However, the speed and magnitude of species responses, including shifts in their distribution, are variable and species specific. Quantifying the effect of environmental conditions on species distributions is crucial to informing management and conservation efforts. Blue marlin (Makaira nigricans) is a wide-ranging top predator occurring circumglobally in tropical and subtropical waters and is heavily impacted by international longline fisheries. This study aimed to predict the global distribution of blue marlin and characterize the effects of climate variability thereon. Location Global. Methods To conduct this study, pop-up satellite archival tags (n = 144) deployed by recreational anglers through a global citizen science programme were used to generate a large tracking data set (14,928 days, 210,983 km from deployment to pop-up locations) of blue marlin movement across three ocean basins. State-space modelled tracking position estimates were used to create a species distribution model to represent global habitat suitability for blue marlin. Habitat suitability was determined by fitting a generalized additive mixed model (GAMM) as a function of environmental covariates which was used to predict monthly global blue marlin habitat from 2000 to 2016. Results Blue marlin habitat preference had the strongest association with sea surface temperature. Seasonal variation in blue marlin habitat occurs primarily at the latitudinal edges of the distribution range. Over the duration of the study, 96% of core habitat declined in suitability, with a concurrent poleward increase in suitability of marginal habitat. Main Conclusions This study highlights the successful application of citizen-based science to develop a long-term global telemetry dataset. The present-day loss of highly suitable habitat suggests ocean warming may be making equatorial waters less suitable even to highly mobile species. Blue marlin is likely to respond by following preferred habitat as it shifts poleward.

Blue shark (Prionace glauca) is amongst the most abundant shark species in international trade, however this highly migratory species has little effective management and the need for spatio-temporal strategies increases, possibly involving the most vulnerable stage or sex classes. We combined 265,595 blue shark observations (capture or satellite tag) with environmental data to present the first global-scale analysis of species’ habitat preferences for five size and sex classes (small juveniles, large juvenile males and females, adult males and females). We leveraged the understanding of blue shark biotic environmental associations to develop two indicators of foraging location: productivity fronts in mesotrophic areas and mesopelagic micronekton in oligotrophic environments. Temperature (at surface and mixed layer depth plus 100 m) and sea surface height anomaly were used to exclude unsuitable abiotic environments. To capture the horizontal and vertical extent of thermal habitat for the blue shark, we defined the temperature niche relative to both sea surface temperature (SST) and the temperature 100 m below the mixed layer depth (Tmld+100). We show that the lifetime foraging niche incorporates highly diverse biotic and abiotic conditions: the blue shark tends to shift from mesotrophic and temperate surface waters during juvenile stages to more oligotrophic and warm surface waters for adults. However, low productivity limits all classes of blue shark habitat in the tropical western North Atlantic, and both low productivity and warm temperatures limit habitat in most of the equatorial Indian Ocean (except for the adult males) and tropical eastern Pacific. Large females tend to have greater habitat overlap with small juveniles than large males, more defined by temperature than productivity preferences. In particular, large juvenile females tend to extend their range into higher latitudes than large males, likely due to greater tolerance to relatively cold waters. Large juvenile and adult females also seem to avoid areas with intermediate SST (~21.7-24.0°C), resulting in separation from large males mostly in the tropical and temperate latitudes in the cold and warm seasons, respectively. The habitat requirements of sensitive size- and sex-specific stages to blue shark population dynamics are essential in management to improve conservation of this near-threatened species.

Background The blue marlin ( Makaira nigricans ) is a vulnerable migratory fish inhabiting tropical and subtropical pelagic waters of the Atlantic, Pacific and Indian Oceans. The biology and spatial ecology of the species in the eastern North Atlantic is poorly understood, despite being exploited in the region by recreational and commercial fisheries. Here, we present results of the first study to use pop-up satellite archival tags to track blue marlin off Madeira, Portugal ( n = 3) and obtain insights into the movements and habitat use of the species within the eastern North Atlantic. Results Blue marlin were tracked for 24 to 83 days, moving from Madeira to pelagic waters off the Canary Islands, Cape Verde Islands, as well as along the continental shelf brake of Europe and Africa. Blue marlin spent 71% of their time in the upper 5 m and 89% in the upper 50 m, though all individuals dived to depths over 200 m (maximum: 336 m). Temperature at depth ranged from 12 to 28.6 °C, but the greatest proportion of time was spent in waters between 20 and 26 °C. Detailed depth and temperature time-series data were obtained from a tag recovered eight years later. These data show clear diel differences in depth use, involving consistent use of the surface at night and deeper dive activity during the day, predominately to depths greater than 50 m. Conclusions The highly migratory patterns of this vulnerable species in the eastern North Atlantic highlights the need for both local and international conservation measures. Depth-use patterns, particularly the high usage of the upper 5 m of the water column, make them susceptible to surface longline fisheries.

Marine protected area (MPA) designs, including large-scale MPAs (LSMPAs; >150,000 km2), mobile MPAs (fluid spatiotemporal boundaries), and MPA networks, may offer different benefits to species and could enhance protection by encompassing spatiotemporal scales of animal movement. We sought to understand how well LSMPAs could benefit nine highly-mobile marine species in the tropics now and into the future by: 1) evaluating current range overlap within a LSMPA; 2) evaluating range overlap under climate change projections; and 3) evaluating how well theoretical MPA designs benefit these nine species. We focused on Palmyra Atoll and Kingman Reef, a 2000 km2 area within the 1.2 million km2 U.S. Pacific Remote Islands Marine National Monument (PRIMNM) that contains marine megafauna (reef and pelagic fishes; sea turtles; seabirds; cetaceans) reflecting different behaviors and habitat use. Our approach is useful for evaluating the effectiveness of the Palmyra-Kingman MPA and PRIMNM in protecting these species, and tropical LSMPAs in general, and for informing future MPA design. Stationary MPAs provided protection at varying scales. Reef manta rays (Mobula alfredi), grey reef sharks (Carcharhinus amblyrhynchos), green sea turtles (Chelonia mydas), and bottlenose dolphins (Tursiops truncatus) had overall small ranges (<100 km from Palmyra-Kingman) and could benefit from stationary MPAs that contained heterogenous reef habitats. Yellowfin tuna (Thunnus albacares), sooty terns (Onychoprion fuscatus), red-footed boobies (Sula sula), great frigatebirds (Fregata minor), and melon-headed whales (Peponocephala electra) navigated complex oceanographic processes and may benefit most from mobile MPAs that shift with features including thermal fronts, cyclic regions of elevated productivity, and eddies, if relationships with these features are established and predictable. All species had capacity to travel to nearby reef systems, illustrating potential benefits of MPA networks and protected corridors. Suitable habitats will likely contract for all species as warm water expands under climate change scenarios (species habitats were predicted to decrease by 4–49% at Palmyra-Kingman) and MPAs may not protect suitable habitats into the future. Species habitat requirements and movement ecologies are critical aspects of marine spatial planning, especially with respect to dynamic ocean processes and a changing climate.

The use of marine animals as ocean observing platforms (OOPs) has been identified by scientists and managers as having the ability to significantly improve existing oceanographic models and data resources. As OOPs, animals are fit with oceanographic sensors with the capacity to measure in situ temperature and conductivity with an accuracy comparable to ship-based conductivity-temperature-depth (CTD) casts or autonomous drifters. While initial applications of this approach focused on regularly surfacing marine mammals, there is significant unrealized potential for non-air-breathing species that still surface regularly (specifically sharks) to sample a wider range of global habitats. Sharks occupy habitats across the globe, in particular habitats that are coincident with hurricanes. One region where sharks have enormous untapped potential to serve as OOPs and directly benefit coastal communities is the Mid-Atlantic Bight (MAB). Using pelagic shark species that occur in the MAB to generate high-quality water column CTD profiles has the potential to greatly improve regional oceanographic and hurricane models by providing real-time oceanographic data to the Integrated Oceanographic Observation System (IOOS) and the Global Telecommunication Service (GTS) which are directly accessed by ocean and atmospheric models. The objective of this paper is to develop an algorithm quantifying the effectiveness of different pelagic shark species to serve as OOPs using a new CTD tag (Sea Mammal Research Unit [SMRU], University of St. Andrews) to collect real-time oceanographic data in the MAB for hurricane prediction applications. To quantify the effectiveness of pelagic species to serve as OOPs, we analyzed Argos smart position and temperature (SPOT) tag data acquired for 14 shark species from 2002 to 2017, as well as transmitted and recovered archival data from pop-up satellite archival (PSAT) tags acquired for four species over the same time period. We assessed the quality of candidate species based on the quantity and type of Argos location classes a species was able to transmit (i.e., time the animal spent at the surface), the frequency of surfacing over time (a proxy for data transmission rates), as well as the range of depths following a surfacing event that a shark species was able to attain in a given time window (i.e. a proxy for the likelihood of receiving transmitted CTD profiles from a given depth under a specified tag battery duty cycle). Results indicate significant cross-species differences in time at surfacing and surfacing rates, with highly migratory and endothermic sharks surfacing more frequently (approximately between once every 6-20 hours) and for longer suggested periods of time (evinced by higher proportions of location classes with lower spatial error) than residential and ectothermic species. Comparisons of the distribution of depths a given species dove to following a surfacing event identified threshold depths for each species, whereafter receiving a CTD cast beyond the threshold depth would be less common and likely require a longer tag duty cycle and greater battery consumption.

Determining population trends is critical for evaluating management actions and prioritizing species protections. In this study, we used empirical data to produce an estimate of the population trend for sub-adult and adult white sharks in central California. We used the unique dorsal fin morphology to build a mark-recapture data set in a modified Jolly-Seber model (POPAN formulation) to estimate annual abundance and then investigate population growth rates using parametric bootstrapping methods for sub-adult and adult sharks (males and females). For all demographic groups combined, we found equivocal evidence for a positive regional population growth (lambda = 1.07 (95% CI = 0.91 to 1.23)). However, sex- and size-specific population growth rate estimates provided some evidence of population increases for reproductively mature males (lambda = 1.06 (95% CI = 0.99 to 1.13)) and females (lambda = 1.06 (95% CI = 0.95 to 1.17)). For sub-adult male and female white sharks, point estimates of lambda were positive but uncertainty prevents strong inference (lambda = 1.07 (95% CI = 0.85 to 1.29)) and (lambda = 1.08 (95% CI = 0.88 to 1.28)), respectively. Our findings of a potential increase in reproductive-aged white sharks in central California may be a result of regional fluxes in density or attributed in part to current protection efforts and subsequent increase in abundance of pinnipeds as well as reduced gill-net fisheries mortality of juveniles. A trend estimate for the entire northeastern Pacific will require obtaining similar data across known aggregation areas along the west coast of North America.

REPLYING TO H. Murua et al. Nature https://doi.org/10.1038/s41586-021-03396-4 (2021) Our previously published paper1 provided global fine-scale spatiotemporal estimates (1° × 1°; monthly) of overlap and fishing exposure risk (FEI) between satellite-tracked shark space use and automatic identification system (AIS) longline fishing effort. We did not assess shark mortality directly, but in addition to replying to the Comment by Murua et al.2, we confirm—using regression analysis of spatially matched data—that fishing-induced pelagic shark mortality (catch per unit effort (CPUE)) is greater where FEI is higher. We focused on assessing shark horizontal spatiotemporal overlap and exposure risk with fisheries because spatial overlap is a major driver of fishing capture susceptibility and previous shark ecological risk assessments (ERAs) assumed a homogenous shark density within species-range distributions3,4,5 or used coarse-scale modelled occurrence data, rather than more ecologically realistic risk estimates in heterogeneous habitats that were selected by sharks over time. Furthermore, our shark spatial exposure risk implicitly accounts for other susceptibility factors with equal or similar probabilities to those commonly used in shark ERAs3,5.

The yellowfin tuna (Thunnus albacares) is a widely distributed, migratory species that supports valuable commercial fisheries throughout their range. Management of migratory species requires knowledge of movement, mixing and key life history parameters such as growth rate, natural and fisheries mortality. Current management is based on the assumptions that the species is highly migratory and populations are well mixed, but these assumptions have been questioned by recent studies. Since November 2015, yellowfin tuna have been tagged with conventional, archival and pop-up satellite tags (PSAT) in the South Atlantic Ocean around St Helena, with the goal of better understanding their movement patterns and ecology in this region. Conventional tags were attached to 4049 yellowfin tuna (size range 24-158 cm fork length, FL), PSAT tags were deployed on 15 yellowfin in inshore St Helena waters (size range 95-138 cm FL) and 7 yellowfin (size range 125-140 cm FL) at Cardno Seamount, and archival tags were deployed on 48 yellowfin tuna in inshore St Helena waters (size range 69-111 cm FL). Most yellowfin tuna remained within 70 km of their release location, suggesting a degree of retention to the region. Although displacement of yellowfin was generally low, the furthest distance travelled between release and recapture location was 2755 km, with other tuna also displaying large-scale movements. Tagging revealed connections between inshore regions and seamounts, as well as links between St Helena waters and key fishing regions and putative spawning grounds in the Gulf of Guinea.

The twilight zone contains the largest biomass of the world's ocean. Identifying its role in the trophic supply and contaminant exposure of marine megafauna constitutes a critical challenge in the context of global change. The white shark (Carcharodon carcharias) is a threatened species with some of the highest concentrations of neurotoxin methylmercury (MeHg) among marine top predators. Large white sharks migrate seasonally from coastal habitats, where they primarily forage on pinnipeds, to oceanic offshore habitats. Tagging studies suggest that while offshore, white sharks may forage at depth on mesopelagic species, yet no biochemical evidence exists. Here, we used mercury isotopic composition to assess the dietary origin of MeHg contamination in white sharks from the Northeast Pacific Ocean. We estimated that a minimum of 72% of the MeHg accumulated by white sharks originates from the consumption of mesopelagic prey, while a maximum of 25% derives from pinnipeds. In addition to highlighting the potential of mercury isotopes to decipher the complex ecological cycle of marine predators, our study provides evidence that the twilight zone constitutes a crucial foraging habitat for these large predators, which had been suspected for over a decade. Climate change is predicted to expand the production of mesopelagic MeHg and modify the mesopelagic biomass globally. Considering the pivotal role of the twilight zone is therefore essential to better predict both MeHg exposure and trophic supply to white sharks, and effectively protect these key vulnerable predators.

Silky sharks (Carcharhinus falciformis) represent a major component of global shark catch, both directly and as bycatch, and populations are declining as a result. An improved understanding of their movement ecology is needed to support conservation efforts. We deployed satellite and acoustic tags (2013–2018) and analyzed historical fisheries records (1997–2009), to investigate the spatial ecology of silky sharks in the central Indian Ocean and a large Marine Protected Area (MPA; 640,000 km2) around the Chagos Archipelago. We observed high fidelity to the MPA, and a sustained diurnal association with a seamount complex, with individuals moving off at night and returning at sunrise. Yet, we also observed large-scale divergent movements in two satellite tagged individuals and documented the furthest recorded displacement distance for a satellite tagged silky shark to date, with one individual moving from the MPA to the Kenyan coast—a displacement distance of 3,549 km (track distance ∼4,782 km). Silky sharks undertook diel vertical migrations and oscillatory diving behavior, spending > 99% of their time in the top 100 m, and diving to depths of greater than 300 m, overlapping directly with typical deployments of purse seine and longline sets in the Indian Ocean. One individual was recorded to a depth of 1,112 m, the deepest recorded silky shark dive to date. Individuals spent 96% of their time at liberty within water temperatures between 24 and 30°C. Historic fisheries data revealed that silky sharks were a major component of the shark community around the archipelago, representing 13.69% of all sharks caught by longlines before the fishery closed in 2010. Over half (55.88%) of all individuals caught by longlines and purse seiners were juveniles. The large proportion of juveniles, coupled with the high site fidelity and residence observed in some individuals, suggests that the MPA could provide considerable conservation benefits for silky sharks, particularly during early life-history stages. However, their high mobility potential necessitates that large MPAs need to be considered in conjunction with fisheries regulations and conservation measures in adjacent EEZs and in areas beyond national jurisdiction.

Large marine protected areas (MPAs) of unprecedented size have recently been established across the global oceans, yet their ability to meet conservation objectives is debated. Key areas of debate include uncertainty over nations' abilities to enforce fishing bans across vast, remote regions and the intensity of human impacts before and after MPA implementation. We used a recently developed vessel tracking data set (produced using Automatic Identification System detections) to quantify the response of industrial fishing fleets to 5 of the largest MPAs established in the Pacific Ocean since 2013. After their implementation, all 5 MPAs successfully kept industrial fishing effort exceptionally low. Detected fishing effort was already low in 4 of the 5 large MPAs prior to MPA implementation, particularly relative to nearby regions that did not receive formal protection. Our results suggest that these large MPAs may present major conservation opportunities in relatively intact ecosystems with low immediate impact to industrial fisheries, but the large MPAs we considered often did not significantly reduce fishing effort because baseline fishing was typically low. It is yet to be determined how large MPAs may shape global ocean conservation in the future if the footprint of human influence continues to expand. Continued improvement in understanding of how large MPAs interact with industrial fisheries is a crucial step toward defining their role in global ocean management.

Pop-up archival tags (n = 16) were deployed on Atlantic bluefin tuna (ABT) off the west coast of Ireland in October and November 2016 (199-246 cm curved fork length), yielding 2799 d of location data and 990 and 989 d of depth and temperature time-series data, respectively. Most daily locations (96%, n = 2651) occurred east of 45 degrees W, the current stock management boundary for ABT. Key habitats occupied were the Bay of Biscay and the Central North Atlantic, with two migratory patterns evident: an east-west group and an eastern resident group. Five out of six tags that remained attached until July 2017 returned to the northeast Atlantic after having migrated as far as the Canary Islands, the Mediterranean Sea (MEDI) and the Central North Atlantic. Tracked bluefin tuna exhibited a diel depth-use pattern occupying shallower depths at night and deeper depths during the day. Four bluefin tuna visited known spawning grounds in the central and western MEDI, and one may have spawned, based on the recovered data showing oscillatory dives transecting the thermocline on 15 nights. These findings demonstrate the complexity of the aggregation of ABT off Ireland and, more broadly in the northeast Atlantic, highlighting the need for dedicated future research to conserve this important aggregation.

Atlantic bluefin tuna (Thunnus thynnus) are highly migratory fish with a contemporary range spanning the North Atlantic Ocean. Bluefin tuna populations have undergone severe decline and the status of the fish within each population remains uncertain. Improved biological knowledge, particularly of natural mortality and rates of mixing of the western (GOM) and eastern (Mediterranean) populations, is key to resolving the current status of the Atlantic bluefin tuna. We evaluated the potential for acoustic tags to yield empirical estimates of mortality and migration rates for long-lived, highly migratory species such as Atlantic bluefin tuna. Bluefin tuna tagged in the Gulf of St. Lawrence (GSL) foraging ground (2009–2016) exhibited high detection rates post release, with 91% crossing receiver lines one year post tagging, 61% detected after year two at large, with detections up to ~1700 days post deployment. Acoustic detections per individual fish ranged from 3 to 4759 receptions. A spatially-structured Bayesian mark recapture model was applied to the acoustic detection data for Atlantic bluefin tuna electronically tagged in the GSL to estimate the rate of instantaneous annual natural mortality. We report a median estimate of 0.10 yr−1 for this experiment. Our results demonstrate that acoustic tags can provide vital fisheries independent estimates for life history parameters critical for improving stock assessment models.

Marine protected areas (MPAs) have become an increasingly important tool to protect and conserve marine resources. However, there remains much debate about how effective MPAs are, especially in terms of their ability to protect mobile marine species such as teleost and chondrichthyan fishes. We used satellite and acoustic tags to assess the ability of a large oceanic MPA, the British Indian Ocean Territory MPA (BIOT MPA), to protect seven species of pelagic and reef-associated teleost and chondrichthyan fishes. We satellite-tagged 26 animals from six species (Blue Marlin, Reef Mantas, Sailfish, Silky Sharks, Silvertip Sharks, and Yellowfin Tuna), producing 2,735 days of movement data. We also acoustically tagged 121 sharks from two species (Grey Reef and Silvertip Sharks), which were monitored for up to 40 months across a large acoustic receiver array spanning the MPA. We found that the activity spaces of all satellite-tagged animals, including pelagic species, were much smaller than the area of the BIOT MPA, even taking into account errors associated with position estimates. Estimates of space use of acoustically tagged sharks, based on dynamic Brownian Bridge Movement Models (dBBMM), were also much smaller than the size of the MPA. However, we found important limitations when using dBBMM and demonstrate its sensitivity to both study duration and array design. We found that Grey Reef Sharks should be monitored for at least 1 year and Silvertip Sharks for 2 years before their activity space can be effectively estimated. We also demonstrate the potentially important role that intraspecific variability in spatial ecology may play in influencing the ability of MPAs to effectively protect populations of mobile species. Overall, our results suggest that, with effective enforcement, MPAs on the scale of the BIOT MPA potentially offer protection to a variety of pelagic and reef species with a range of spatial ecologies. We suggest that animals need to be tagged across seasons, years, and ontogenetic stages, in order to fully characterize their spatial ecology, which is fundamental to developing and implementing effective MPAs to conserve the full life history of target species.