Seasonal Spatial Segregation In Blue Sharks (Prionace Glauca) By Sex And Size Class In The Northeast Pacific Ocean Seasonal spatial segregation in blue sharks (Prionace glauca) by sex and size class in the Northeast Pacific Ocean Diversity and Distributions

Aim Animal 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. Location Northeast Pacific Ocean. Methods We 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. Results We found that there was spatial segregation between sex-size classes particularly in the summer months with immature females found largely north of 33 degrees N, and males south of 35 degrees N. In fall, females travelled south, resulting in an overlap in distributions south of 37 degrees 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 degrees 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 conclusions We 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. Grant no. NA14NMF4720312 Grant no. NA14OAR4170075