Marine mammal physiology
Many questions related to the conservation of marine mammals cannot be easily addressed using empirical approaches. We strive to identify and address these questions using mathematical and simulation modeling, capitalizing on existing data. We have several prior and ongoing project in this area.
Determining the metabolic rate of swimming polar bears
Climate change is causing more rapid and earlier breakup of sea ice in the Artic each summer. One consequence of this is that polar bears are being forced into longer and more frequent swims. Swimming is assumed to be an energetically costly behavior, but it was unclear just how much energy was required. In 2017 I published a paper that estimated the metabolic costs of swimming for polar bears of different sizes using data available on the internal temperature of a bear that swam for 9 days through cold Artic waters. It also identified the lower size limit where polar bear cubs can engage in long swims without experiencing problems with hypothermia. You can see a summary of the findings of this study in this video, or listen to a podcast that discusses the work here, or read about it in a news story here. In addition, Utah Public Radio did a feature on this work in their weekly broadcast UnDisciplined with Matthew Leplante. You can hear the show here.
Determining when southern elephant seal females should skip reproduction.
Female elephant seals are capable of reproducing every year, yet this process is energetically very costly and results is extensive weight loss. If females cannot sufficiently replace lost body mass during annual foraging periods, their low body mass results in small pups that have low chances for survival. Evolution should produce reproductive strategies that maximize the fitness of individual anaimals. I used an optimality modeling approach to determine the optimal reproductive strategy for female southern elephant seals, highlighting the age and body size when a female should forego current reproduction and focus instead on mass gain to ensure future reproductive success. Further, this model examined the role of ocean conditions that vary with El Niño cycles, and also examined how optimal strategies are influenced by differences in the foraging abilities of individual females. You can read this study here.
How does foraging on whale bone piles influence reproductive strategies of polar bears?
Alaskan and Canadian indigenous people capture whales annually as part of their cultural practices and deposit the bones at specific locations (i.e., bone piles) along the coast of the Southern Beaufort Sea. Polar bears that are forced ashore during ice free periods are known to forage at these bone piles, and bears that use this strategy generally have better body condition than their counterparts that do not use these bone piles. An ongoing collaboration between my lab and John Whiteman at Old Dominion University uses a combination of mathematicala and optimality modeling to determine how use of this alternative food source should influence the reproductive strategy of female polar bears.
Optimal reproductive strategies of female sea otters
Sea otters were historically hunted to near extinction along the Pacific North American coast. Subsequent protection and reintroductions have helped this species to partially recover. Population growth depends on successful reproduction, and the reproductive strategy of otters puts an extreme stress on females, leading a large portion of females to literally work themselves to death raising pups, particularly in areas where food resources are scarce. Females in poor body condition will at times abondon pups before they are ready to fend for themselves. Yet it remains unclear when this early termination of pup care should be expected. An ogoing collaboration between my lab and Nicole Thometz at the University of San Francisco uses optimality modeling to determine when female otters should choose to continue pup care and when they should abandon the pup in order to ensure their own survival and future reproductive opportunities. This model contrasts areas of central California that provide high or low quality foraging habitats.