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.
A long standing question in neuroethology is how fish localize sound underwater. While terrestrial animals use the delay in sound reaching each ear to determine the origin of the sound, this option is not readily available to aquatic animals as sound travels five times faster underwater and fish hearing organs are in close proximity. The marine toadfish, Opsanus tau, provides an excellent model to study sound localization as males will acoustically attract females their habitat. Microwire electrodes were chronically implanted into the auditory and mechanosensory and neural activity was recorded in freely moving fish in response to naturally relevant stimuli. It was determined that both the auditory and lateral line can detect toadfish vocalizations. Both systems are sensitive to the frequency of the toadfish signal and show directional sensitivity, indicating they have the potential to localize the sound. Although the auditory endorgans or otoliths appear too close to use time delay for sound localization, the neuromasts of the lateral line are widespread and could be optimally suited for this task. However, both of these sensory systems have dual roles, as the otoliths encode horizontal fish movement when swimming and the lateral line is primarily involved in detecting small water displacement. Future goals will be to determine how these sensory systems integrate model modal sensory input. Five undergraduate students, including two from underrepresented groups received training during the project. Three are currently in graduate school in the biological sciences with a fourth matriculating this fall. Four post-doctoral fellows participated in the project and all currently now have faculty appointments. A middle school science teacher participated in two summers of the student and incorporated aspects of the study into her curriculum.
