The Influence Of Habitat Complexity, Prey Quality, And Predator Avoidance On Sea Otter Resource Selection In Alaska

Abstract

The differential selection of habitat by animals is one of the fundamental relationships that enable species to coexist. Habitat selection may be among various discrete categories (e.g., mudflat, boulder field, or meadow) or among a continuous array of characteristics such as vegetation percent cover, benthic substrate size, substrate rugosity, distance to prey resources, or distance to suitable escape terrain from predation. Sea otters are particularly suitable for resource selection studies because they are capable of selecting a wide variety habitat types in response to prey availability, competition, and predation. In Alaska, sea otters associate with a range of habitats types including continuous bedrock reefs in the western Aleutians to heterogeneous fjord systems in Kackemak Bay, Lower Cook Inlet. Sea otters inhabiting the western Aleutians exhibit highly restricted habitat selection patterns characteristic of declining populations. In contrast, sea otters inhabiting Kachemak Bay exhibit selective use of a broad range of habitat types. Many factors contribute to the selective use of habitats by animals, including habitat suitability, prey quality, and predation risk. This thesis was designed to test factors contributing to sea otter resource selection in an area undergoing population increase versus an area experiencing high predation pressure. The contribution of prey size, abundance, biomass, potential energy density are considered in addition to physical habitat characteristics such as grain size, rugosity, depth, structural habitat complexity, and exposure to prevailing weather. Findings suggest that foraging sea otters differentially select habitat and prey resources based on prey accessibility and not on prey abundance or potential prey energy density. Findings further suggest that sea otter foraging site selection is based on habitat complexity in areas with increasing populations, but in areas with high predation pressure, proximity to suitable escape terrain appears to be more important than prey quality or benthic habitat complexity.