It’s the eye of the tiger (shark)! Animal-mounted cameras reveal how tiger sharks spot and track prey

Cameras on animals now give scientists unprecedented access to the visual world of animals, including the life and death struggles of hunters and their prey.

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

Small video camera tags were attached to tiger sharks at Ningaloo Reef, Western Australia, by an international team of scientists from Macquarie University, the Australian Institute of Marine Science, the University of Western Australia, Murdoch University, the Stanford University and Oregon State University. A virtual visual system for sharks was used to process beacon videos to understand how these predators visually experience interactions with sea ​​turtlescommon prey.

The video tags also contained motion sensors to track the small-scale movements of sharks, allowing monitoring of swimming behavior and the shark’s reaction to turtles.

This is the first study to examine images from an animal-based camera through the visual abilities of the animal on which they are mounted, allowing researchers to obtain a more accurate representation of life through the eyes of a tiger shark.

“When we look at the raw camera footage of tiger sharks approaching sea turtles, it seemed odd that often tiger sharks would swim directly above a turtle sitting on the reef, a potentially easy meal,” says lead author Dr Laura Ryan from the School of Natural Sciences at Macquarie University.

“However, when we look at visual cues through the tiger shark’s visual system, it is actually extremely difficult to detect the turtle, and particularly when it is standing still, blending into the background may allow it to camouflage against attacks.”

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

The researchers tracked the fine-scale movements of the sharks, which helped to monitor their swimming behavior, finding that apex predators investigated turtles that stood out visually in depth.

The visual detection of a turtle was accompanied by a change in the behavior of the tiger shark, showing that despite low acuity, vision remains a key sensory system for these animals. Once a sea turtle was spotted, the sharks slowed down and made numerous turns, suggesting they had entered search mode for their prey.

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

“This likely reflects the fact that these sharks inhabit generally nutrient-poor environments, and these predators need to be careful not to expend too much energy chasing prey to prepare a meal.”

The study gives a better insight into the use of visual cues in prey identification by tiger sharks and camouflage strategies used by sea turtles to avoid predation. The team now wants to apply the approach to other species.

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

Follow the tail beats 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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