Satellite telemetry reveals higher fishing mortality rates than previously estimated, suggesting overfishing of an apex marine predator

Byrne, Michael E.; Cortés, Enric; Vaudo, Jeremy J.; Harvey, Guy; Sampson, Mark; Wetherbee, Bradley M.; Shivji, Mahmood S.

doi:10.1098/rspb.2017.0658

Cited by 44 publications

(50 citation statements)

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“…By characterizing multiple movement behaviors of satellitetracked sharks and identifying environmental characteristics associated with resident movements, we demonstrate behaviorally-based patterns of habitat use which we contrast between regions, highlighting the regionally variable influence of habitat characteristics on movement patterns of a single species. Additionally, recent analyses indicate mako sharks in the North Atlantic are facing significant overfishing (Byrne et al 2017, ICCAT 2017. Thus, quantifying how the effects of environmental covariates vary between regions has practical application to effective conservation measures that rely on predicting and reducing fisheries interactions.…”

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confidence: 99%

Behavioral response of a mobile marine predator to environmental variables differs across ecoregions

et al. 2019

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Animal movement and habitat selection are in part a response to landscape heterogeneity. Many studies of movement and habitat selection necessarily use environmental covariates that are readily available over large‐scales, which are assumed representative of functional habitat features such as resource availability. For widely distributed species, response to such covariates may not be consistent across ecosystems, as response to any specific covariate is driven by its biological relevance within the context of each ecosystem. Thus, the study of any widely distributed species within a limited geographic region may provide inferences that are not widely generalizable. Our goal was to evaluate the response of a marine predator to a suite of environmental covariates across a wide ecological gradient. We identified two behavioral states (resident and transient) in the movements of shortfin mako sharks Isurus oxyrinchus tracked via satellite telemetry in two regions of the western North Atlantic Ocean: the tropical Caribbean/Gulf of Mexico marginal sea (CGM), and the temperate waters of the open western Atlantic Ocean (OWA). We compared patterns of resident behavior between regions, and modeled relationships between oceanographic variables and resident behavior. We tracked 39 sharks during 2013–2015. Resident behavior was associated with shallow, continental shelf and slope waters in both regions. In the OWA resident behavior was associated with low sea surface temperature and high primary productivity, however, sharks exhibited no response to either variable in the CGM. There was a negative relationship between sea‐surface height gradient (a proxy for oceanic fronts) and resident behavior in the OWA, and a positive relationship in the CGM. Our observations likely reflect shark responses to regional variability in factors responsible for the distribution and availability of prey. Our study illustrates the importance of studying widely distributed species in a consistent manner over large spatial scales.

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Section: Introductionmentioning

confidence: 99%

Behavioral response of a mobile marine predator to environmental variables differs across ecoregions

et al. 2019

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“…Recently, Byrne et al. () used satellite‐tag data from Smart Position Only Transmitters (SPOT) to estimate annual fishing mortality of shortfin mako sharks Isurus oxyrinchus in the Atlantic Ocean. To our knowledge, this was the first study to use satellite‐tag data of any kind from a marine species (aside from sea turtles) to estimate annual survival rates and model factors influencing fisheries mortality risk using known‐fate models (Byrne et al., ).…”

Section: Introductionmentioning

confidence: 99%

“…() used satellite‐tag data from Smart Position Only Transmitters (SPOT) to estimate annual fishing mortality of shortfin mako sharks Isurus oxyrinchus in the Atlantic Ocean. To our knowledge, this was the first study to use satellite‐tag data of any kind from a marine species (aside from sea turtles) to estimate annual survival rates and model factors influencing fisheries mortality risk using known‐fate models (Byrne et al., ). However, SPOT tags do not allow for reliable detection of natural mortality events and are only effective on certain fish species, such as sharks that surface regularly and have rigid dorsal fins (Byrne et al., ; Drymon & Wells, ).…”

Section: Introductionmentioning

confidence: 99%

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Juvenile survival, competing risks, and spatial variation in mortality risk of a marine apex predator

Benson

Jorgensen

O’Sullivan

et al. 2018

Journal of Applied Ecology

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Reliable estimates of mortality have been a major gap in our understanding of population ecology for marine animals. This is especially true for juveniles, which are often the most vulnerable age class and whose survival can strongly influence population growth. Thousands of pop‐up archival satellite tags (PAT) have been deployed on a variety of marine species, but analysis of these data has mainly been restricted to movement ecology and post‐handling survival following fisheries bycatch. We used PAT data to provide empirical estimates of annual survival and cause‐specific mortality for juveniles of a marine top predator. We tagged and tracked juvenile white sharks in the north eastern Pacific Ocean to (1) estimate survival rates and competing risks and (2) investigate intrinsic and environmental influences on mortality risk. We also evaluated the use of PAT data with respect to meeting assumptions of known‐fate survival models. Annual juvenile survival rate was 0.632 (SE = 0.15) and annual natural mortality rate (0.08, SE = 0.06) was lower than the rate of gillnet interactions (0.48, SE = 0.15). Mortality risk decreased with greater body length and was significantly greater (hazard ratio = 9.05, SE = 0.70) for juvenile sharks in Mexican waters, relative to California waters. The PAT data allowed for unambiguous determination of fate in most cases, aided by collaborative relationships with fishers and secondary tags deployed on a subset of sharks. Although caution must be exercised to establish whether assumptions are met, our work demonstrates that PAT data represent a widely available, untapped data source that could dramatically increase our understanding of marine population ecology. Synthesis and applications. Our research shows fisheries bycatch to be the main source of mortality for juvenile white sharks in the northeastern Pacific Ocean, highlighting the need for best practices, such as releasing sharks quickly following incidental capture. Furthermore, mortality risk for juveniles was greater in Mexican waters, such that survival may be lower in colder years when juveniles are likely to move south seeking warmer water. This could increase stochasticity in juvenile survival and negatively influence population growth for this apex predator.

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“…; Byrne et al. ). For many marine species, acquiring movement data is often challenging due to poor access to study sites and low encounter success (Lennox et al.…”

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First Observations of Long‐Distance Migration in a Large Skate Species, the Winter Skate: Implications for Population Connectivity, Ecosystem Dynamics, and Management

et al. 2019

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The overexploitation and decline of groundfish populations throughout the 1980s and 1990s resulted in a regime shift on Georges Bank and southern New England, which was characterized by subsequent exponential increases in the observed biomass of Winter Skate Leucoraja ocellata in the region. Recent work suggested that the rate of the Winter Skate biomass increase cannot be fully explained by internal population dynamics of a population without immigration from other regions and/or populations and that adult‐mediated population connectivity (AMPC) with neighboring regions is required to fully explain biomass trends. Despite this, no evidence of long‐distance dispersal has been observed for Winter Skate, with individuals assumed to display high endemicity to specific regions of the continental shelf. Annual movements of 58 Winter Skate captured off coastal New York were examined using passive acoustic telemetry, revealing seasonal long‐distance dispersal capabilities exceeding 1,000 km. In total, 88,783 unique acoustic detections were observed. Telemetered individuals had an average time at liberty of 199.73 d and collectively traveled 17,576.9 km. Individuals tended to migrate south during summer/fall and north during winter/spring. Movement rates of individuals averaged 9.88 km/d (95% confidence interval = 9.25–10.92 km/d) but ranged from 0.13 to 41.38 km/d. An additional 51 recaptured Winter Skate from a total of 3,416 marked with Floy tags suggested greater offshore movement than was observed in acoustically tagged individuals. Our results illustrate that the Winter Skate is a highly mobile species that moves extensively throughout its large geographic range, consistent with its observed ability to rapidly invade neighboring habitat via AMPC. This study has important implications for our understanding of the role of Winter Skate in northwest Atlantic communities and for management strategies therein.

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Satellite telemetry reveals higher fishing mortality rates than previously estimated, suggesting overfishing of an apex marine predator

Cited by 44 publications

References 48 publications

Behavioral response of a mobile marine predator to environmental variables differs across ecoregions

Behavioral response of a mobile marine predator to environmental variables differs across ecoregions

Juvenile survival, competing risks, and spatial variation in mortality risk of a marine apex predator

First Observations of Long‐Distance Migration in a Large Skate Species, the Winter Skate: Implications for Population Connectivity, Ecosystem Dynamics, and Management

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