The influence of environmental and anthropogenic variables on whale shark (rhincodon typus) abundance in the south ari Atoll

Abstract

Rhincodon typus is a large filter feeding elasmobranch that aggregates in shallow coastal waters such as the South Ari atoll Marine Protected Area (S.A. MPA) in the Maldives. They are known to travel large distances, however little is known about what causes these movements throughout the oceans and into aggregation sites. This study aims to determine whether whale shark seasonality is present in the South Ari Atoll as well as recognise what environmental and anthropogenic factors influence whale shark abundance in the area. Whale shark sightings data collected by the Maldives Whale Shark Research Programme (MWSRP) from the S.A. MPA from 2013 to 2016 was analysed for seasonality and then relationships with variables using correlations and linear regression. It was discovered that there was no seasonality between months in the years from 2013 to 2016. Therefore it is assumed there is a subpopulation of whale sharks in the South Ari Atoll remaining loyal to the area. Whale shark abundance for all years increases with Sea Surface Temperature anomaly (SSTa) most likely due to the optimal functioning of the shark’s metabolism being within this temperature causing them to remain within a specific range. Average maximum number of people present on the day had a negative effect on abundance for all years, most likely due to prolonged exposure to humans leading to avoidance behaviour by local whale sharks. Overall it was thought that the local subpopulation moved into the South Ari Atoll dependent on SST and the number of people swimming on the reef. This analysis along with further research may allow further insight into the drivers and timings of aggregations. It may also serve to highlight the implications on the distribution and aggregations of whale sharks from increasing temperatures due to climate change as well as the impact on their behaviour from ecotourism.