Revealing the Predator’s View: Tiger Sharks Vs. Sea Turtles in the Visual Arms Race
The battle of predator-prey dynamics in nature has always been changing in our world. It’s an ongoing “evolutionary arms race” where prey will develop strategies to avoid being hunted, and predators adapt to become better at hunting.
The most significant turning point in this evolutionary race was image-forming eyes, which dated back approximately 530 million years ago. The rise of Image-forming eyes was during the Cambrian period, which was the start of the extreme diversification of life forms. To combat the predation-enhancing traits, some strategies, such as camouflage, were created. This set up the predator-prey dances we witness in nature today.
Camouflage is a classic survival strategy that takes on many forms- from morphological adaptations such as transparency and color matching to more intricate strategies such as motion camouflage.
With the help from the Coral Bay Research Station at Murdoch University in Western Australia, researchers Laura A. Ryan, Samantha Andrzejaczek, Adrian C. Gleiss, Mark G. Meekan, Taylor K. Chapple, and Nathan S. Hart were able to research the interactions from visual perspectives of tiger sharks to determine how effective it is in their skillful hunting.
The tiger sharks’s vision is vital for prey detection, specifically at the surface when they hunt for their preferred prey, sea turtles. They have evolved refined retinal adaptions to enhance their visions despite being colorblind. Their proficiency comes down to detecting motion, which involves factors such as spatial and temporal resolution and contrast sensitivity. This is far more impressive than the 20/20 vision some humans have!
The core of this research lies in their use of animal-borne video cameras, or in other words, shark-borne cameras. The team used these cameras to closely observe sea turtles’ visibility through the eyes of tiger sharks and recorded their behavioral responses. To further investigate the visual aspect, they also employed a 2DMD (two-dimensional motion detector) model capable of capturing the strength of visual motion signals generated by sea turtles. The data on background, water visibility, direction of shark approach, sea turtle speed, and size were all collected. The swimming metrics were also collected from sensor data. This methodology aimed to discover the visual cues that guide tiger sharks while hunting and strategies sea turtles use to avoid predation.
In total, 18 interactions between tiger sharks and sea turtles were observed, which revealed a surprising trend: sea turtles displayed greater motion cues than their backgrounds, indicating high visibility. In addition, the strength of these cues remained consistent in all directions, suggesting that their motion cues are remarkably uniform and easy for tiger sharks to spot them from all angles.
These are both valuable insights into the visual dynamics of predator-prey interactions, highlighting visual cues and the importance of a shark’s visual perception, which suggests that sea turtles are more visible to sharks than we originally thought.
Ryan, L. A., Andrzejaczek, S., Gleiss, A. C., Meekan, M. G., Chapple, T. K., & Hart, N. S. 2022. Prey interactions in tiger sharks: Accounting for visual perception in animal-borne cameras. Journal of Experimental Marine Biology and Ecology, 553, 151764.
