Intraspecific differences in movement, dive behavior and vertical habitat preferences of a key marine apex predator

Abstract

Understanding the patterns of large-scale movements of highly mobile marine predators is essential to understanding the impacts of anthropogenic pressures on the animals and the ecosystems they frequent. The broadnose sevengill shark Notorynchus cepedianus is one of the most important apex predators in temperate coastal areas around the world, yet little is known of its seasonal large-scale movements. Five male and five female sevengill sharks were equipped with pop-up satellite archival tags (PSATs) in a coastal embayment in southern Tasmania, that collected depth and temperature data during winter, when the animals leave the coastal embayment, resulting in a dataset covering a total of 818 d. Animal tracks indicated that males moved northwards into warmer waters, whereas females remained in southern waters. Three of the females stayed in the Tasmanian coastal areas while the other two left, with one of them moving into deeper waters of up to 360 m depth at the southern edge of the Tasmanian shelf before returning to the Tasmanian coast. These sex-specific differences in large-scale movement could potentially lead to the differential exploitation of the sexes when the sharks leave the protected areas where they were tagged. Both males and females switched between diel vertical migration and reverse diel vertical migration over the course of their tracks and displayed oscillatory vertical movements, probably linked to foraging. These vertical movements persisted throughout the tracks, suggesting that sevengill sharks foraged continuously during their migration rather than switching between transiting and foraging modes. © Inter-Research and CSIRO 2014.