The comparative abundance and behaviour of sharks in the Cayman Islands (BWI)
Kohler, Johanna Katharina
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This thesis investigates the ecology of coastal sharks, in particular the Caribbean reef shark (Carcharhinus perezi), using data collected in the Cayman Islands from 2009 to 2019. Relative abundance was estimated by deploying 936 Baited Remote Underwater Video Systems (BRUVS) and individual shark behaviour monitored by recording the movement of 66 acoustically tagged Caribbean reef sharks. This work was complemented by information gathered on 24,442 dives by 69 SCUBA divers participating in a citizen science programme (the ‘Sharklogger Network’). Additionally, population sizes for two species were estimated through the application of mark-recapture models to the sighting histories of sharks individually identified on 557 BRUVS videos deployed between 2015 and 2018. The study recorded eight shark species of which Caribbean reef and Atlantic nurse shark (Ginglymostoma cirratum) were the most abundant, with estimated local coastal population sizes of 180 and 336 respectively. Immature and mature Caribbean reef, nurse, and hammerhead (Sphyrna) sharks were recorded throughout the year, suggesting resident breeding populations. Most Caribbean reef and nurse sharks showed relatively small home ranges (< 20 km) and high site-fidelity. However, some individuals showed maturity-based seasonal movements indicating a distinct mating and pupping season, with a few detected moving more than 100 km.