Dive Types Matter: They Reveal the Foraging Ecology of Elephant Seals

Abstract

AbstractThe different two-dimensional shapes of dives of reveal much about the foraging ecology of elephant seals (Mirounga spp.). We give a brief history of dive typing, instrument development that improved and validated the process, and address what dive types reveal about foraging strategies, foraging success, and foraging location. Dive types were initially classified by visual inspection and later with Principal Component Analysis and Clustering, or machine-learning algorithms. Time-depth recorders, with the additional measure of swim speed, yield four major dive types: pelagic foraging, benthic foraging, transit, and drift dives. Geolocation, 3D measures, and other sensors confirm the principal dive types and add additional relevant information about diving and the environment. Dive types have revealed that females forage pelagically over deep water in the open ocean on prey in the deep scattering layer, whereas males forage benthically near continental slopes. Transit dives are used to get to and from foraging sites. Passive drift dives may serve the funtions of digestion, rest, and sleep. The direction of drifting reflects buoyancy, which changes as the seal feeds, thus giving a measure of foraging success. Sex-specific differences in dive types indicative of foraging begin to appear at two years of age. Dive typing has also been used to describe the foraging ecology of other pinnipeds as well as cetaceans.