Abstract
AbstractAimAnimal tracking can provide unique insights into the ecology and conservation of marine species, such as the partitioning of habitat, including differences between life history stages or sexes, and can inform fisheries stock assessments, bycatch reduction and spatial management such as dynamic management.LocationNortheast Pacific Ocean.MethodsWe used satellite tracking data from 47 blue sharks (Prionace glauca) from the Northeast Pacific to determine movements and home range along the west coast of North America, and sex–size class (immature females, mature males) specific habitat preferences using boosted regression trees. Using a suite of static and dynamic environmental variables, we determined distribution and habitat preferences across summer and fall for each sex–size class.ResultsWe found that there was spatial segregation between sex–size classes particularly in the summer months with immature females found largely north of 33°N, and males south of 35°N. In fall, females travelled south, resulting in an overlap in distributions south of 37°N. Sea surface temperature (SST), latitude and longitude were top predictors. However, immature females and adult males demonstrated unique habitat preferences including SST, with immature females preferring cooler temperatures (SST < 15°C) than adult males in summer, and a broader band of SST than adult males in fall. All models performed well, explaining 50%–67% of deviance, and 23%–41% of deviance when predictions were cross‐validated.Main conclusionsWe provide first insights into coastal movements and habitat preferences of blue sharks in the Northeast Pacific. We found that immature females undergo a seasonal southward migration in this more coastal habitat, similar to patterns observed in the North Atlantic. We also found some overlap between adult males and immature females in fall months, suggesting the importance of more coastal habitat in managing this species, particularly in determining population structure for blue shark stock assessments, and reducing blue shark bycatch.
Highlights
Understanding the relationship between animal distribution and environmental features can be useful for determining appropriate management and conservation actions
Our study found that in more coastal regions of the Northeast Pacific, there is sex and size class segregation among blue sharks and resulting differences in habitat preference
Immature females were found further north, while male habitat occurred in the southern portion of the study area (Figure 1); overlap does occur in the Southern California Bight for both core and overall home ranges, with core home range of males almost entirely overlapped by a portion of female core home range in that region (Figure 2)
Summary
Understanding the relationship between animal distribution and environmental features can be useful for determining appropriate management and conservation actions. In the North Pacific, Nakano (1994) proposed that juvenile males are largely located between 30‐35oN, juvenile females north of 35‐40oN and adults located throughout the North Pacific, with mating taking place between 20‐30oN; this distribution is known as the “north–south model” (hereafter “N–S model”; Nakano, 1994; Nakano & Seki, 2003) Strong evidence for this pattern in the Central Pacific is provided by bycatch data (Walsh & Teo, 2012), and evidence of a similar pattern exists in the North and South Atlantic from bycatch and tracking data (Montealegre‐ Quijano & Vooren, 2010; Vandeperre, Aires‐da‐Silva, Fontes, et al, 2014a; Vandeperre, Aires‐da‐Silva, Santos, et al, 2014b). We use blue shark satellite tracking data and habitat modelling to address this knowledge gap through (a) identifying seasonal home range and key habitat areas in more coastal waters in the Northeast Pacific; (b) exploring the physical drivers of habitat selection across seasons; and (c) examining how the influence of these drivers varies among sexes and size classes across seasons. We discuss the implications of these findings for the management of blue shark populations along the US west coast
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