It's the tiger's eye (the shark)!  Animal-borne cameras reveal how tiger sharks detect and track prey

It’s the tiger’s eye (the shark)! Animal-borne cameras reveal how tiger sharks detect and track prey

Animal-borne cameras now give researchers unmatched access to the visual world of animals, including the battle of hunters and their prey for life and death.

For the first time, new research, published in Journal of Experimental Marine Biology and Ecologyhas combined knowledge of the structure of the eyes tiger sharks with images of prey and habitats from small cameras deployed on these animals. This enabled the development of a virtual visual system for the shark, which enabled researchers to analyze videos of hunting behavior through the eyes of this first-class predator.

Small camcorder tags are attached Tiger sharks at Ningaloo Reef, in Western Australia by an international team of researchers from Macquarie University, the Australian Institute of Marine Science, the University of Western Australia, Murdoch University, Stanford University and Oregon State University. A virtual visual system for the sharks was used to process the videos from the tags to understand how these predators visually experience interactions with sea ‚Äč‚Äčturtlesa common exchange object.

The video tags also contained motion sensors to track fine-scale movements of the sharks, which means that swimming behavior and the shark’s reaction to turtles can be monitored.

This is the first study to look at animal-borne camera footage through the visual ability of the animal they are mounted on, allowing researchers to get a more true picture of life through the eyes of a tiger shark.

“When you look at the raw camera images of tiger sharks approaching sea turtles it seemed strange that tiger sharks often swam directly over a turtle sitting on the reef, a potentially light meal “, says lead author Dr Laura Ryan from the School of Natural Sciences at Macquarie University.

“But when we look at the visual cues through the tiger shark’s visual system, it’s actually extremely difficult to spot the turtle, and especially when they remain immobile, mixing in the background can allow them to camouflage themselves from attack.”

“Tiger sharks have much lower visual acuity than humans and camcorders. This means that sharks must rely on some form of movement from the sea turtles to be able to identify them. For sea turtles, their best form of defense against attack may be to simply remain still in the presence of the predator, “says Dr. Ryan.

The researchers tracked the sharks’ fine-scale movements, which made it possible to monitor their swimming behavior, and discovered that the tips of the predators thoroughly examined the turtles that visually protruded.

The visual discovery of a turtle was accompanied by a change in the tiger shark’s behavior, which shows that despite low sharpness, vision is still a central sensory system for these animals. When a sea turtle was spotted, sharks slowed down and made many turns, indicating that they had entered a search mode for their prey.

“The image that emerges through the shark’s eyes is an almost slow hunt for a slow-moving prey, rather than a high-speed ambush that we tend to think of when we see other large predators in action, such as white sharks,” says co-author Dr. Samantha Andrzejaczek from Hopkins Marine Station at Stanford University.

“This probably reflects the fact that these sharks live in environments that are generally poor in nutrients, and these predators need to be careful not to put too much energy into hunting prey to make a meal.”

The study provides greater insights into the use of visual cues in change identification of tiger sharks and the camouflage strategies used by sea turtles to avoid predation. The team now wants to apply the method to other species.

“Animal-borne cameras are now common in the field of ecology, but few researchers have taken the next step to really consider the videos they provide in terms of what the animals can actually see. This is the next limit for this form of tagging,” said co-author Dr Mark Meekan of the Australian Institute of Marine Science.

Trace the tail stroke of a tiger shark

More information:
Laura A. Ryan et al, Prey interactions in tiger sharks: Accounting for visual perception in animal-borne cameras, Journal of Experimental Marine Biology and Ecology (2022). DOI: 10.1016 / j.jembe.2022.151764

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