Does bathymetry drive whale shark aggregations?

Abstract

Whale sharks, Rhincodon typus, form seasonal feeding aggregations in coastal waters around the world. Most research has studied individual aggregations and prey availability, without investigating factors known to influence other megafauna aggregations. A number of studies have shown the basking shark and megamouth shark, are more abundant in areas with bathymetric features known to cause higher primary productivity. Therefore, this study examines the bathymetry in areas R. typus aggregation events occur, with the aim to understand whether bathymetry influences aggregations. The research carried out shows there are similarities in bathymetry between aggregation sites, significantly different from other coastal areas within R. typus’ global range. Evidence shows aggregations occur in areas with specific bathymetric features; shallow coastal areas in close proximity to water in the mesopelagic zone, connected by steep gradient slopes such as reef slopes or continental shelf breaks. These factors are known to induce upwelling events, increasing primary productivity, consequently attracting a number of filter feeding species. This study has shown bathymetry does influence Rhincodon typus aggregations and has filled in knowledge gaps missing from previous research.