The biochemical and physiological limits to diving in marine mammals focus on two absolute restrictions: how long can the animal hold its breath and how deep can it dive? There are still many aspects of these two questions that remain a mystery, particularly with respect to the effects of high pressures associated with deep diving, and the cues that drive the animal back to the surface to breathe. This broad-based research program focuses primarily on two specific areas of study. The first is the study of pressure tolerance adaptations in marine mammal blood and tissues. This is a very new area in the study of marine mammal diving adaptations, and very little is known about how pressure impacts diving performance, and subsequently, how these animals make their living at depth. Recent findings of apparently damaging effects of nitrogen in stranded whales suggest that marine mammals may employ some of the same behavioral strategies as human divers to avoid the damaging effects of pressure on physiological systems, in addition to possessing biochemical and/or physiological adaptations. An improved understanding of these processes in marine mammals may have implications for better understanding the nature of diving injury in humans. The second area of focus is increasing our understanding of the physiological cues that signal a diving animal that it is reaching the limits of its oxygen stores, and how they manage their time at the surface. It has been generally assumed that the post-dive surface interval was driven by the need to refill the body's oxygen stores. However, recent work suggests that carbon dioxide may also play an important role. It's also possible that keeping the surface interval short is one way that marine mammals might reduce the cost of finding food in the face of seasonal changes in the food supply, long-term shifts in ocean conditions, unusual climate events such as El Nino, and in response to human impacts. This project will be the first study to examine the physiology of the post-dive recovery period specific to questions of how marine mammals use this portion of the dive cycle as part of a cost-saving strategy. Ultimately, improving our knowledge of how marine mammals cope with the challenges of life at depth is critical in the development of management strategies for the animals, their prey and their habitat.
