Influences of Temporal Changes in Pelagic Scattering Layers on Short-Finned Pilot Whales Behavior

Abstract

To understand the distribution of deep diving odontocetes, it is important to investigate the relationship between the foraging whales and their prey. Short-finned pilot whales mainly feed on squid and occasionally fish. Foraging short-finned pilot whales off the Island of Hawaii were located using trained visual observers and a passive acoustic hydrophone or a hydrophone array. A 500 meter by 500-meter survey box was set up over the foraging sites. A two-frequency split-beam echosounder collected micronekton backscatter over foraging and non-foraging control sites of the same location and similar time of day. Nautical Area Scattering Coefficient (NASC) (m2nmi−2) profiles were compared over the water column between foraging and non-foraging populations to analyze the relationship between micronekton density and short-finned pilot whale foraging. Using a generalized additive mixed model and a generalized linear mixed model, it was determined that short-finned pilot whales were able to exploit the daily variation of micronekton preferring to forage when the relative biomass was higher, and the deep scattering layer was found at shallower depths suggesting that there was more prey at accessible depths for the whales to feed on.