Spatial modeling of haul-out site use by harbor seals in Cook Inlet, Alaska

Abstract

Harbor seals Phoca vitulina haul out on land to give birth to and rear their pups, rest, escape aquatic predation and molt. The choice of a haul-out site is therefore fundamental to survival and reproduction. Aerial surveys of harbor seals were conducted in Cook Inlet, Alaska, to investigate the seals' selection of various environmental characteristics of haul-out sites. Eight surveys from April, June, August and October were performed to understand how haul-out site use varies season- ally. A GIS database describing all potential haul-out habitats in the study area was created by acquiring separate data sets on bathymetry, sea-bed type, proximity to sources of anthropogenic dis- turbance, prey availability, biological wave exposure and substrate type. Because harbor seal abun- dance and several environmental features varied temporally, 4 separate models were developed to account for conditions specific to each survey month. Spatial regression analyses, which allowed data to be spatially autocorrelated, were used to identify the relationships between harbor seal abundance and environmental variables associated with haul-out sites. Harbor seals were found to haul out near available prey and to avoid areas high in anthropogenic disturbance. The seals also selected haul-out sites of rock substrate and those that were near deep water.