PhD Candidate - University of Alaska Fairbanks
Tiger sharks are found circumglobally in tropical and warm-water coastal and oceanic ecosystems (Randall 1992). As the largest apex predator in many of these ecosystems, tiger sharks (Galeocerdo cuvier) regulate lower trophic levels through both direct consumption and behavioural modification of prey (Heithaus 2012). Loss of large bodied, top predators is linked to large-scale changes to ecosystems and strong trophic cascades (Estes 2011). Tiger sharks are a highly mobile species, capable of 7,500 km migrations in a year, but have also shown philopatry to distinct areas (Lea et al. 2015). Due to this highly mobile nature, tiger sharks are likely to inhabit and regulate several ecosystems (Heupel et al. 2014).
To better understand movement patterns, residency time, and potential returns to Bimini, acoustic tags were implanted in both young-of-year/juvenile and mature tiger sharks. These tags were recorded anytime a shark came within approximately 500m of a receiver. The array of Shark Lab receivers around Bimini were used in conjunction with other collaborative receiver arrays throughout the region.
Longline surveys and deepline surveys were used to assess the influence of season and location on the catch rates of juvenile and mature tiger sharks. Additionally, stable isotope analysis was used to assess possible ontogentic shifts in prey selection, and an ultrasound was used to determine if mature females were pregnant when captured around Bimini.
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Establishing what areas sharks are using during key life stages is important for conservation and management efforts. Understanding dispersal patterns is essential for creating accurate population models, creating effective regulations, and determining the rebound potential of species. Observing how sharks are interacting with the longlines will help to establish is particular size classes and species are being underrepresented in these surveys. Additionally it may be possible to determine how to intentionally reduce shark capture on commercial longlines.