Assessing the environmental and biological variables that make South Ari Atoll Marine Protected Area (SAMPA) a world renowned whale shark aggregation site

Abstract

Whale sharks (Rhincodon typus) typically aggregate in response to seasonal increases in prey abundance, with phytoplankton blooms as well as fish and coral spawning events attracting large numbers of sharks. However, the whale sharks of South Ari Atoll Marine Protected Area (SAMPA) show extraordinary site fidelity, with a predictable year round population and no seasonal peak in aggregations. Whale sharks are slow to reach sexual maturity and vulnerable to overexploitation, which has resulted in a decline in global populations by >50% over the last 75 years. This study assesses the environmental and biological variables driving whale shark aggregations at SAMPA in order to improve whale shark conservation strategies. The whale shark encounter and environmental data used in this study were collected by the MWSRP team from the 1st of January 2014 to the 18th of April 2017. Surveys were conducted from Dhigurah to Rangali along the epipelagic reef fringe in a local vessel. A mean of whale sharks per day (shark encounters/search effort) and 12 environmental variables were calculated to allow for accurate comparisons between data using a Gaussian Generalised Linear Model (GLM). Of these variables, chlorophyll a (P=0.0217) and current strength (P=0.0058) were found to have a significant relationship with mean whale sharks per day (α=0.026). The environmental and biological variables analysed were found to affect the year round aggregation of whale sharks at SAMPA, but the primary drivers of site fidelity remain unknown