Predicting Cetacean Habitats from Their Energetic Needs and the Distribution of Their Prey in Two Contrasted Tropical Regions
Résumé
To date, most habitat models of cetaceans have relied on static and oceanographic covariates, and very few have related
cetaceans directly to the distribution of their prey, as a result of the limited availability of prey data. By simulating the
distribution of six functional micronekton groups between the surface and .1,000 m deep, the SEAPODYM model provides
valuable insights into prey distributions. We used SEAPODYM outputs to investigate the habitat of three cetacean guilds
with increasing energy requirements: sperm and beaked whales, Globicephalinae and Delphininae. We expected High
Energy Requirements cetaceans to preferentially forage in habitats of high prey biomass and/or production, where they
might easily meet their high energetic needs, and Low Energy Requirements cetaceans to forage in habitats of either high
or low prey biomass and/or production. Cetacean sightings were collected from dedicated aerial surveys in the South West
Indian Ocean (SWIO) and French Polynesia (FP). We examined cetacean densities in relation to simulated distributions of
their potential prey using Generalised Additive Models and predicted their habitats in both regions. Results supported their
known diving abilities, with Delphininae mostly related to prey present in the upper layers of the water column, and
Globicephalinae and sperm and beaked whales also related to prey present in deeper layers. Explained deviances ranged
from 9% for sperm and beaked whales in the SWIO to 47% for Globicephalinae in FP. Delphininae and Globicephalinae
appeared to select areas where high prey biomass and/or production were available at shallow depths. In contrast, sperm
and beaked whales showed less clear habitat selection. Using simulated prey distributions as predictors in cetacean habitat
models is crucial to understand their strategies of habitat selection in the three dimensions of the ocean.