Understanding the physiological mechanisms and energetics that determine the ecological niche of an organism will remain central to my research program. As we continue to see the effects of climate change and anthropogenic stressors, this information is essential for predicting and mitigating ecosystem responses to the changing environment. My research program combines “basic” science with “applied” science by examining the physiological mechanisms and energetics that determine the diving capacity, thermal tolerance, and reproductive and foraging strategies of air-breathing marine vertebrates. 

Current Research

Field energetics and diving physiology of a small cetacean, the harbor porpoise (in collaboration with Drs. Peter Madsen and Tobias Wang


Cetaceans are among the largest animals ever to evolve, and as apex predators in marine ecosystems, they have a significant top-down effect on prey targeted during long, deep breath-hold dives.  It is therefore essential to understand the energetic requirements and oxygen management of cetaceans if we are to interpret and understand their role in the trophic energy cascades, their foraging ecology, limits of dive performance and ability to adapt to environmental change and disturbance.  However, very little is known about the field physiology of cetaceans due their size and hostile habitats.  At the Fjord and Bælt center (Kerteminde, Denmark) a unique opportunity exists to measure metabolic rate, heart rate, and activity in captive porpoises that live in a large net pen experiencing similar conditions to wild porpoises.  By having access to this one of a kind facility, we will be able to compare these data on captive porpoises to heart rate and activity data of wild porpoises in the same Danish waters.  This provides a unique opportunity to examine the field energetics and diving physiology of a wild cetacean.  

We are investigating the energetic requirements and oxygen management strategy during diving in the harbor porpoise.  The three main objectives are: 1) Determine the field metabolic rate of harbor porpoises using a combination of field and laboratory studies; 2)  Measure heart rate in freely diving harbor porpoises, which will for the first time document the level of bradycardia in a naturally diving cetacean; and 3) Determine muscle workload/activity during dives.  


Diving physiology of the California sea lion: Blood oxygen depletion, heart rate, and stroke rate in free ranging sea lions (in collaboration with Dr. Paul Ponganis)


This project will contribute to our understanding of oxygen management and the underlying physiological mechanisms of oxygen management in marine mammals.  This information is essential if we are to interpret and understand the limits of dive performance, foraging ecology, and the ability of breath hold divers to adapt to environmental change and disturbance.  In this study we will determine the rate and magnitude of oxygen store depletion during dives, and investigate its relationship to heart rate and workload, thereby improving our understanding of oxygen management during diving, specifically the role of lung oxygen stores and oxygen delivery to tissues. 

We are using backpack digital recorders to measure blood oxygen depletion, heart rate, and flipper stroke rate in dives of California sea lions during maternal foraging trips to sea from San Nicolas Island.  The goals of this research are: 1) determination of the rate, pattern and magnitude of blood oxygen store depletion during both shallow and deep dives at sea, 2) documentation of heart rate profiles of shallow and deep dives, and assessment of the relationship between changes in heart rate to blood oxygen profiles, and 3) documentation of flipper stroke rate profiles during shallow and deep dives, and assessment of the relationship of stroke rate to both changes in heart rate and changes in blood oxygen profiles.


Emperor penguin post-molt foraging behavior (P.I. Gerald Kooyman)


Emperor penguins dive deeper and longer, fast longer, and endure the harshest weather conditions of all diving birds. They spend about four to five months after the breeding season deep in Antarctic pack ice, far from shore and any stations.  During this time they undergo great changes in body weight as they feed to recover from the breeding season, lose weight while fasting during the molt, and then continue to feed before the breeding season.  Unfortunately due to their remote location little is known about the foraging ecology and diving behavior during this critical period.  This study will fill an important gap in what we know about the biology of the annual cycle of the emperor by examining the molt-post molt period. In March of 2013 we travelled deep into the Antarctic pack ice in the Eastern Ross Sea to instrument emperor penguins after they molted.  The objectives of the study were: 1) Place satellite/time depth recorder tags on 20 adult post molt birds to determine their route, rate of travel, and diving behavior as they return back to their breeding colonies, 2) Obtain an index of body condition, 3) Collect guano to determine the type of food consumed by emperor penguins in the region, 4) Conduct shipboard surveys to sight and plot the location and abundance of adult and juvenile birds on the ship's track. You can check out the blogs and video from the cruise here: Scripps Blog,  Tracers Blog,  National Geographic Blog, Time-lapse video

Physiological Biologger development and testing (in collaboration with Drs. Tobias Wang and Peter Madsen)

As part of my postdoctoral research in Denmark I am modifying and testing a physiological data logger to measure blood flow, blood pressure and heart rate in a freely diving marine mammal.  Ultimately, this logger will be deployed on a freely diving seal, measuring blood flow and cardiac output, the result of which will increase our understanding of oxygen store management in marine mammals.


Past Research Projects

  • Blood oxygen depletion in diving California sea lions

  • The reproductive energetics of Antarctic fur seals: influence of maternal traits and foraging behavior on investment

  • Diving heart rate in free ranging emperor penguins

  • Foraging behavior and habitat utilization of southern elephant seals

  • Foraging behavior and habitat utilization of crabeater seals along the western Antarctic Peninsula

  • Foraging energetics of Galapagos sea lions

  • Physiological behavioral determinants of lactation efficiency in northern elephant seals

  • Foraging behavior and diving physiology of northern elephant seals