Abstract
Tiger sharks (Galeocerdo cuvier) are a wide ranging, potentially keystone predator species that display a variety of horizontal movement patterns, making use of coastal and pelagic waters. Far less, however, is known about their vertical movements and use of the water column. We used pop-up satellite archival tags with two data sampling rates (high rate and standard rate tags) to investigate the vertical habitat use and diving behavior of tiger sharks tagged on the Puerto Rico–Virgin Islands platform and off Bermuda between 2008 and 2009. Useable data were received from nine of 14 sharks tagged, tracked over a total of 529 days. Sharks spent the majority of their time making yo-yo dives within the upper 50 m of the water column and considerable time within the upper 5 m of the water column. As a result, sharks typically occupied a narrow daily temperature range (∼2°C). Dives to greater than 200 m were common, and all sharks made dives to at least 250 m, with one shark reaching a depth of 828 m. Despite some similarities among individuals, a great deal of intraspecific variability in vertical habit use was observed. Four distinct depth distributions that were not related to tagging location, horizontal movements, sex, or size were detected. In addition, similar depth distributions did not necessitate similar dive patterns among sharks. Recognition of intraspecific variability in habitat use of top predators can be crucial for effective management of these species and for understanding their influence on ecosystem dynamics.
Highlights
Marine ecosystems by virtue of their three dimensional habitat allow evolution of a complex interaction of horizontal and vertical movements by highly mobile species, including large apex predators
Tiger sharks (Galeocerdo cuvier) are a wide ranging, potentially keystone predator species that display a variety of horizontal movement patterns, making use of coastal and pelagic waters
Tiger sharks tracked in the Caribbean and western North Atlantic showed a number of broad similarities in overall vertical habitat use, and striking differences in the vertical movements among individuals apparently unrelated to sex, size, horizontal movements, or the physical environment
Summary
Marine ecosystems by virtue of their three dimensional habitat allow evolution of a complex interaction of horizontal and vertical movements by highly mobile species, including large apex predators. Many shark species are large mobile predators that occupy upper trophic levels (Cortes 1999), and as such their movements are of great interest for the above reasons as well as for understanding their interactions with fisheries and making informed management efforts. Sharks have been the focus of many movement studies using a variety of telemetry technologies. Most of these studies, have focused on horizontal move-
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