Ravenous Trevally Feasting on Vast Schools of Whale Shark Prey Fish

Ningaloo Reef in Western Australia is a frequent haunt of whale sharks, where these enormous creatures can often be seen gracefully navigating through the water, surrounded by swarms of thousands of small carangid baitfishes, each measuring approximately 10cm in length.

Previously, it was believed that these little fish accompanied the massive whale sharks for protection, assuming they were safe from predation in their company. However, recent research conducted by the Harry Butler Institute at Murdoch University has shed new light on this phenomenon. The study, published in Marine Biology, unveils that large schools of trevally, measuring over 30cm in length, engage in rapid feeding frenzies, lasting anywhere from two to 45 seconds, during which they consume entire schools of baitfishes.

These findings challenge the notion that baitfishes simply seek safety near the world’s largest fish, the whale sharks, which can grow up to an astonishing 18 meters in length. Christine Barry, the lead author of the study and a Ph.D. candidate at the HBI’s Center for Sustainable Aquatic Ecosystems and the Australian Institute of Marine Science, analyzed footage from cameras attached to juvenile whale sharks (up to 7 meters in length) and an opportunistically captured video by a Ningaloo tourism photographer.

Barry suggests that the association of baitfishes with whale sharks at Ningaloo Reef may not primarily be for protection against predation. Instead, it could be driven by energetic advantages and improved access to food resources. She explains that whale sharks in this region actively seek out dense food patches, and the accompanying baitfishes save valuable energy by riding the bow wave created by the whale sharks as they move through the water.

Furthermore, despite the significant size difference between the baitfish and whale sharks, both species feed on the same food source, such as plankton. Remarkably, the consumption of baitfishes has a negligible impact on the resources available to the whale sharks. This suggests that the association between baitfishes and whale sharks forms a mutually beneficial relationship, where the baitfishes enjoy enhanced mobility and greater access to food opportunities.

However, the trevally’s dramatic feeding frenzies, captured in videos, highlight the vulnerability of these small fish to predatory species when they accompany their gigantic companions, underscoring the complex dynamics of life at Ningaloo Reef.

Source: Murdoch University

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