Abstract
Knowledge of the habitat use and migration patterns of large sharks is important for assessing the effectiveness of large predator Marine Protected Areas (MPAs), vulnerability to fisheries and environmental influences, and management of shark–human interactions. Here we compare movement, reef-fidelity, and ocean migration for tiger sharks, Galeocerdo cuvier, across the Coral Sea, with an emphasis on New Caledonia. Thirty-three tiger sharks (1.54 to 3.9 m total length) were tagged with passive acoustic transmitters and their localised movements monitored on receiver arrays in New Caledonia, the Chesterfield and Lord Howe Islands in the Coral Sea, and the east coast of Queensland, Australia. Satellite tags were also used to determine habitat use and movements among habitats across the Coral Sea. Sub-adults and one male adult tiger shark displayed year-round residency in the Chesterfields with two females tagged in the Chesterfields and detected on the Great Barrier Reef, Australia, after 591 and 842 days respectively. In coastal barrier reefs, tiger sharks were transient at acoustic arrays and each individual demonstrated a unique pattern of occurrence. From 2009 to 2013, fourteen sharks with satellite and acoustic tags undertook wide-ranging movements up to 1114 km across the Coral Sea with eight detected back on acoustic arrays up to 405 days after being tagged. Tiger sharks dove 1136 m and utilised three-dimensional activity spaces averaged at 2360 km3. The Chesterfield Islands appear to be important habitat for sub-adults and adult male tiger sharks. Management strategies need to consider the wide-ranging movements of large (sub-adult and adult) male and female tiger sharks at the individual level, whereas fidelity to specific coastal reefs may be consistent across groups of individuals. Coastal barrier reef MPAs, however, only afford brief protection for large tiger sharks, therefore determining the importance of other oceanic Coral Sea reefs should be a priority for future research.
Highlights
Recent studies have highlighted the critical role that sharks play in regulating food chain diversity through top-down control [1], [2], [3]
Characteristics of Acoustic and Satellite Tagged Sharks Thirty-four tiger sharks 154–390 cm total length (TL) were captured across five study locations between October 2008 and October 2012 (Table 1)
Our results suggest discrete groups of tiger sharks across the Coral Sea utilise specific coral reefs incorporating nearby deep water oceanic environments 98 to 249 km from the location of tagging with three-dimensional activity spaces typically ranging from 0.16 to 4.486103 km3
Summary
Recent studies have highlighted the critical role that sharks play in regulating food chain diversity through top-down control [1], [2], [3]. Sandin et al [6] used underwater visual censuses at reef sites with different densities of top predators to show that fish species targeted by sharks tended to allocate more energy to reproduction than to somatic storage This phenomenon led to increased biomass because of more individuals in spite of their smaller size compared to sites without sharks. There is a critical need to support shark conservation through a better understanding of their ecology to insure the balance and long-term resilience of marine ecosystems [10] This global conservation goal may be achieved using tools such as Marine Protected Areas (MPAs) at several spatial scales [11]. Identifying the movement patterns and habitat-use of key tropical shark species is essential for their conservation
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