An ethogram for the whale shark (Rhincodon typus) with insights into foraging plasticity

Abstract

Whale sharks ( Rhincodon typus ) are large filter-feeders that reside in oligotrophic tropical waters. The feeding behaviours that enable these sharks to survive in such nutrient poor environments are not well understood beyond the surface. Here, we develop a species ethogram and synthesise foraging behaviours by combining observations reported in the literature (106 articles) with data collected by animal-borne cameras (22.5 h) deployed on five whale sharks at a known foraging site at Ningaloo Reef, Western Australia. The ethogram resulted in 36 behaviours, 12 of which involved foraging and six that were novel feeding behaviours recorded by animal-borne cameras. To understand and contextualise the six novel feeding behaviours, we developed a foraging framework that delineated between feeding modality (suction or ram filtration), specific feeding behaviours, and feeding category (stationary, slow or active movement). From the animal-borne video footage, we found slow feeding behaviours to be the most frequent. The ethogram revealed whale sharks forage using different feeding types and movements, and may feed in a cost-effective manner across a very broad range of prey densities, in contrast to other large filter feeders such as baleen whales and basking sharks, which target and limit feeding to dense aggregations of prey. Such behavioural flexibility may be a key attribute that allows these large filter feeding sharks to survive in oligotrophic tropical environments.

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