Understanding how animals navigate under water is not only fascinating in its own right, it also contributes to instrumentation designs of underwater vehicles, robots and surface vessels, impacts management of fisheries, and helps protect the marine environment. Sharks have been chosen to demonstrate how they navigate. While they can not detect a drop of blood a mile away, as often stated, sharks do have impressive prey tracking capabilities. Sharks are important in fisheries worldwide and have been severely depleted in recent decades, often taken as unwanted by-catch in other fisheries. Yet, they are essential top predators needed to maintaining a healthy ecosystem. This research project will show how sharks use all their senses in hunting behavior, starting with initial prey detection, through tracking and locating, and ending with striking their prey. For more complete understanding, we compare a few shark species that appear to use their senses differently mostly because they specialize in different prey in different habitats. A team of experts in sensory and shark biology, using unique testing facilities in Massachusetts and Florida, has been assembled including graduate students being trained in the many technical approaches needed for work on live sharks. The research directly involves undergraduate and high school students and provides extensive outreach to other students of all ages and to the public in general. The accumulated knowledge should lead to a model of shark navigation and predation that can be used for the conservation of sharks, protection of humans, and the engineering design of underwater steering algorithms. The inevitable presentation of this research in future television programs and video documentaries will disseminate new knowledge to the public at large, both of sharks and of rigorous science.
How animals sense and locate their prey -- and particularly how they use multiple senses like vision and smell to integrate sensory information -- has long been a topic of interest to the public as well as research scientists. Although we have known something about this for animals that live on land or in the air, our knowledge of animals that live in the sea has been limited on this subject. To address this, we conducted research on one of the sea's most well-adapted predators -- the shark. Through a series of experiments on live sharks in the laboratory, we challenged these animals to show us how they detect, localize, get to, and feed on their prey, and how they use their multiple senses together to accomplish these tasks. We didn't just work on one type of shark but examined this question in four different species: the smooth dogfish, the nurse shark, the blacktip shark and the bonnethead. These four species have differing behaviors and ecologies in that some are more bottom-dwelling while others are more active swimmers in the water column. The senses we tested were vision and smell and two other senses that humans don't have. These other two are a sort of underwater sense of distant touch mediated by a system called the lateral line, and also electroreception, a sense that sharks have to detect weak electric fields surrounding their prey. By selectively blocking each sense one at a time, we were able to see how sharks use their various senses for orienting to, striking at, and capturing their prey. The results were fascinating. Each species showed a different preference for sensory information depending on their behavior and ecology. For example, in the blacktip shark vision was dominant, in the nurse shark it was smell, and in the bonnethead it was electroreception. But they all took advantage of all their available senses. By blocking senses in different combinations, we found that when some of the sharks' normal sensory cues were unavailable, they were still capable of successfully detecting, tracking and capturing their prey by switching to alternate sensory information. This means that sharks are adaptable in using whatever sensory information is available to find their prey -- a good thing in a successful predator. Our research showed how sharks do this, and these findings can now be studied and applied to the design of underwater robotic vehicles that must navigate to some type of target. So in the end, this research taught us a lot about how sharks work, how the senses of animals are integrated in performing complex tasks, and how we can apply this information to engineer better tools for society's use.
