Comparative Habitat Utilization of the Blue Shark (Prionace glauca) and Shortfin Mako (Isurus oxyrinchus)

species common in western North Atlantic continental shelf waters during summer months. Both undergo seasonal migrations to warmer or southern locations. Mako sharks are regional endotherms that maintain elevated temperatures in specific body parts, whereas blue sharks are typical ectotherms. Despite striking physiological and morphological differences between these species, they utilize roughly the same habitat on the continental shelf. To compare fine-scale habitat use of these two species we used pop-up satellite tags which archive depth, temperature, and light to examine environmental utilization of blue (n=10) and shortfin mako (n=6) sharks during migrations away from the shelf. All blue shark and two shortfin mako displayed long-distance migrations. Both blue and mako sharks occupied water of similar depth and temperature on the shelf, despite different prey preferences. During migration, mean depth of blue sharks was 85m compared to 50m for mako sharks. Both blue and shortfin mako sharks utilized 16-22 °C waters for 75% and 60% of their time, respectively. Both species dove frequently during migration with maximum recorded depths of 855m for a blue shark and 866m for a mako. The greatest straight-line distance traveled by a blue shark was 2485km (Cape Cod to Puerto Rico) and 2100km for a mako (Cape Cod to the Bahamas). Differences between these species while on the continental shelf appear to reflect prey consumption rather than habitat utilization; whereas, during migration the two species exhibited more pronounced differences in habitat utilization