Environmental Perturbations, Behavioral Change, and Population Response in a Long-term Northern Elephant Seal Study

Abstract

Abstract : A major challenge in marine mammal conservation and management is to understand how behavioral responses affect populations. To address this challenge, the National Research Council established the Committee on Characterizing Biologically Significant Marine Mammal Behavior. This committee developed a framework for analyzing the population consequences of acoustic disturbance, or PCAD (NRC 2005). The PCAD framework defines a series of transfer functions which describe how behavioral responses to sound affect life functions, how life functions are linked to vital population rates, and how changes in vital rates cause population change (Fig. 1). The U.S. Navy included the PCAD framework in the U.S. Navy Living Marine Resource Sound Research Requirements, specifically within the Response to Naval Sounds requirement #5: Determine biologically significant behavioral responses from Navy sound sources on individuals representing marine mammal species of concern with respect to ... determining long-term effects of behavioral responses and how individual vital rates may affect the population. This requirement was given the highest priority under the Navy's requirements. Implementing the concepts of transfer functions which link behavior to population change, however, requires substantial long-term data on individual animals and population size, and there are few marine mammal populations where quantifying the functions is plausible. Funding from this grant has allowed us to extend and improve a four-decade study of northern elephant seal populations in California, aiming specifically to quantify key linkages within the PCAD model. Since 1968, several thousand individual seals have been tagged and tracked for their lifetimes, and several hundred of those have been weighed or outfitted with telemetry devices in order to document pelagic foraging behavior and body condition.