Modeling as a complementary tool to acoustic data for understanding the impact of environmental disasters on marine mammals

Abstract

This study is focused on how environmental disasters, such as the Deepwater Horizon oil rig explosion in 2010, affect the dynamics of marine mammal populations, particularly sperm whales and beaked whales, in the Northern Gulf of Mexico. We briefly describe how modeling techniques are used to estimate densities of marine mammals using passive acoustic data. We then develop a matrix model to examine the possible long-term effects of a disaster. We consider cases in which the effects of a disturbance result in reductions in either survival (lethal impacts) or fecundity (sublethal impacts). This model, combined with demographic stochasticity, allows us to study the long-term recovery process following an environmental disaster. In particular, recovery probabilities and recovery times of the population are computed, and formulas are derived to compute the sensitivity of the recovery time to changes in properties of the population or the environmental disturbance. We then extend the modeling methodology to consider how marine mammals may be affected by the response of their prey population to a disturbance. Our analysis highlights the difficulty of projecting impacts and recovery in the absence of detailed demographic data, and the value of population models in exploring scenarios and identifying important processes and general relationships. [This research was made possible in part by a grant from The Gulf of Mexico Research Initiative.]