Whale Sharks feeding on baitballs in Western Australia – rare video & analysis from the CSIRO

Whale sharks (Rhincodon typus) feed on baitfish with other predators at Ningaloo Reef.

Baitballs attract large numbers of predators from a wide range of species that aim to capitalise on these dense patches of energy-rich prey.

Whale sharks are a slow moving, filter feeding species that have been observed feeding on baitballs, and may use the herding behaviour of other predators to capture baitfishes and fulfil their large energetic demands, eye-witnesses have reported whale sharks feeding on baitballs for 20 years (Andrewartha 1993), however, there is a lack of in-water photographic evidence to support these reports. This limits our understanding of both the importance of baitballs to whale shark diets and the feeding behaviours employed by whale sharks to capitalise on this food source in this region. 

Over 20 000 tourists participate in whale shark tours at Ningaloo every year and this large amount of time spent in the field increases the likelihood of recording cryptic behaviours. Such opportunistic in-water records can provide a critical insight into ephemeral events that are hard to predict.

Here we present in-water evidence of whale sharks feeding on baitballs during four separate occasions at Coral Bay, Ningaloo. These events were recorded opportunistically by tourism operators.

The baitfishes were not identified in situ and it was not possible to identify the species from photographs or video. During all four events, whale sharks exhibited ram feeding and vertical feeding, where the shark remained stationary, positioned its body in a vertical orientation and fed on baitfishes using a suction technique.

In one observation, whale sharks and other predators made repeated predation attempts on a baitball. These other predators included whaler sharks, trevally, mackerel tuna and wedge-tailed shearwaters.

Tuna and trevally were observed herding the baitball into a tight formation from below, thus trapping it against the surface. At this time, whale sharks and whaler sharks swam through the centre and made predation attempts through the dense patches. 

In contrast, wedge- tailed shearwaters, trevally and mackerel tuna concentrated their foraging attempts on the edge of the baitball, targeting smaller groups of isolated fish. 

Our observations provide evidence of the complexity of whale shark feeding behavior and provides a compelling insight into the interactions of this species with other predatory taxa in the region. While more research is required to further investigate the importance of baitfishes as a prey item to whale sharks at Ningaloo, our results highlight the value of citizen science to collect data that advances our understanding of the ecology of cryptic and elusive species.

From the CSIRO – original article here

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