How gray whales find food: A novel approach offers insight into the factors that drive gray whale foraging at a local scale

Abstract

The population of gray whales (Eschrichtius robustus) that forage seasonally on macro-zooplankton along the coast of Port Orford, Oregon, offer an opportunity to explore the important yet understudied dynamics of these animals and their prey at a local scale. During the 2016 foraging season, GoPro video footage of the water column was used to measure prey distribution and density (n = 198) while individual gray whales were non-invasively tracked using a theodolite (n = 11). In addition, environmental parameters were measured including water depth, distance to kelp, and habitat type. An analysis of these data provides evidence that distance to kelp and depth have significant negative relationships with gray whale foraging effort. The study provides new insight into understanding the complexity of gray whale foraging and highlights the benefits and limitations of using video analysis methods in related studies.