Numerical models of bowhead and gray whale migration in Alaskan waters

Abstract

Numerical models of migrating bowhead and gray whales were developed as part of a larger project to assess the probability that these endangered marine mammals will encounter spilled oil in Alaskan waters. The distribution of animals is represented in space and time by discrete points, each of which may represent one or more whales. The movement of a whale point is governed by a random walk algorithm which follows stochastically a migratory pathway. The migration models rely on sightings of whales to define mean migration pathways. Distances traveled over 3–6 months, divided by the travel time, were used to estimate mean migratory speeds over appropriate sections of the migration route. Stochastic velocity components were added such that maximum instanteneous swimming speeds did not exceed those observed. Modeled whale densities were then compared with field estimates at various times and locations, as available, and mean migration speeds were adjusted locally to calibrate the model. The model proved to be an extremely useful tool for exploring the raw observational data, making clear a number of inconsistencies therein.