70. Pacific Walrus Response to Rapidly Accelerating Arctic Change: Bioenergetics Modeling to Inform Forecasting of Future Population Status

The objective to be achieved by research under this Opportunity is the development of a bioenergetics model to estimate the food requirements for Pacific walruses (Odobenus rosmarus divergens) of different ages and sex classes by time of year. In concert with the overall walrus research program at the U.S. Geological Survey (USGS), this baseline bioenergetics model for the Pacific walrus will then be linked to models of sea ice and benthic prey to determine how changes in diet and sea-ice coverage will affect the energy requirements, life history parameters, and ultimately population dynamics of Pacific walrus.

The Pacific walrus is one of four marine mammal species managed by the Department of the Interior. Walruses feed on clams and other organisms in sediments on the sea floor. Sea ice is important to walruses because it provides them with a platform for accessing productive offshore habitats of the continental shelves. In summer, female walruses and their young follow the sea ice as it retreats north of the Bering Strait and into the Chukchi Sea. Sea ice in the Chukchi Sea has decreased sharply in recent years due to climate warming. In the past decade, the retreat of sea ice in the Chukchi Sea has been more dramatic than in any other area of the Arctic. The record-breaking sea ice minimum in 2007 is believed to be the cause of an unprecedented number of female and young walruses coming ashore during the absence of sea ice over the continental shelf in fall. In 2008, the U.S. Fish and Wildlife Service (FWS) were petitioned to list the Pacific walrus as threatened under the Endangered Species Act (ESA). The petition listed concerns of walruses�f reduced access to offshore foraging areas during increasingly longer ice-free periods.

In response to the growing information needs about Pacific walrus, the USGS has developed a strategic plan to make maximal use of existing data and guide the collection of new data. The core of the plan is a modeling framework that links a walrus population dynamics model with input from a walrus bioenergetics model. Estimates of walrus energy available for storage and respiration will be conditioned on spatial model scenarios of sea ice and benthic prey distribution. Decreased sea-ice coverage will likely alter the diets and behaviours (foraging, resting habits, and so on) of the Pacific walrus. Such changes are expected in turn to negatively affect the energy budgets and capacity of walruses to survive and reproduce. However, the extent to which environmental change interacts with individual behavior, physiology, and population demography has not yet been investigated and is not known with any precision. As such, it is not yet possible to predict how the distribution and numbers of walruses are most likely to respond to global warming.

The successful postdoctoral researcher will lead development of the bioenergetic model for walruses. The bioenegetics model can be parameterized using data from published captive and field studies on walruses, or can be estimated from other pinniped studies if walrus-based estimates are unavailable. Energy requirement parameters in this dynamic model will need to be adjusted for sex and age of walruses as well as different reproductive states, seasonal requirements and activity levels. The bioenergetic model will also need to be extended to the population energy requirements from population composition estimates by age and sex classes. A sensitivity analysis will need to be performed to validate the model.

Several parameters in the bioenergetic model will be dependent on environmental factors. For example, activity levels are dependent on time spent foraging at sea, prey distribution and availability, and so on. Changes in sea-ice coverage and prey distribution as predicted by the benthic and ice models will need to be input into the bioenergetic model by converting changes in environmental conditions into changes in energy requirements for walruses. For example, if sea-ice coverage recession increases foraging effort (including travelling longer, diving deeper, and so on) and decreases the foraging efficiency of walruses; activity will increase while resting time will decrease. This increase in energy output can be compensated either by increasing food intake, by reducing energy allocated to other functions such as reproduction (decrease in reproductive rate expected), or by releasing energy stores from the body (which are limited) to fuel basic metabolic functions.

Energy inputs that are insufficient to cover basic energy needs in a given environment (estimated using foraging efficiency, digestive capacity, prey distribution analyses) will reduce the energy available for reproduction and the probability of surviving. This will need to be partitioned by age and sex classes. This will allow us to draw conclusions on how predicted rates of reproduction and survival will change over time. Monte Carlo simulations will be needed to allow the uncertainty in the predictions to be described and quantified.

Proposed Duty Station: Anchorage, AK

Areas of Ph.D.: Biology, ecology, wildlife biology, wildlife ecology, wildlife physiology (Candidates holding a Ph.D. in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered.)

Qualifications: Applicants must meet one of the following qualifications: Research Wildlife Biologist, Research Ecologist, Research Physiologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Chadwick Jay, (907) 786-7414, cjay@usgs.gov; Karen Oakley, (907) 786-7076, koakley@usgs.gov

Human Resources Office contact: Candace Azevedo, (916) 278-9393, caazevedo@usgs.gov

Summary of Opportunities