Migration and habitat utilization in lamnid sharks

Understanding the movements, habitat utilization, and life history of high trophic level animals is essential to understanding how ecosystems function. Furthermore, large pelagic vertebrates, including sharks, are declining globally, yet the movements and habitats of most species are unknown. A variety of satellite telemetry techniques are used to elucidate the movements and habitat utilization of two species of lamnid shark. Salmon sharks used a subarctic to subtropical niche, and undertook long distance seasonal migrations between subarctic and subtropical regions of the eastern North Pacific, exhibiting the greatest focal area behavior in the rich neritic waters off Alaska and California, and showing more transitory behaviors in pelagic waters where productivity is lower. The timing of salmon shark aggregations in both Alaska and California waters appears to correspond with life history events of an important group of prey species, Pacific salmon. The enhanced expression of excitation-contraction coupling proteins in salmon shark hearts likely underlies its ability to maintain heart function at cold temperatures and their niche expansion into subarctic seas. Adult white sharks undertake long distance seasonal migrations from the coast of California to an offshore focal area 2500 km west of the Baja Peninsula, as well as Hawaii. A full migration cycle from the coast to the offshore focal area and back was documented. During the offshore migration, white sharks frequently swam at the surface. Sharks remained in the offshore focal area for up to 167 d, where they exhibited a broad depth distribution with intensive oscillatory behavior, possibly associated with feeding or mating. Young-of-the-year sharks remained south of Point Conception whereas one three-year-old shark moved north to Point Reyes, California. All juvenile white sharks displayed a diel change in behavior, with deeper mean positions during dawn, day and dusk than during night. Juvenile white sharks are captured as bycatch in both US and Mexican waters, suggesting that management of fishing mortality should be of increased concern. The ability of lamnid sharks to undertake rapid long distance migrations is essential in enabling them to integrate the productivity of distant regions.