Sea Otter Foraging Habits and Effects on Prey Populations and Communities in Soft-Bottom Environments

Abstract

Sea otter populations have made dramatic recoveries during the last 75 years and today play a major functional role in some nearshore communities (Estes and Palmisano 1974; Estes et al. 1978; Duggins 1980; Breen et al. 1982; Estes et al. 1982). Sea otters have considerable influence on the distribution, abundance, and demography of their benthic invertebrate prey (Ebert 1968; Lowry and Pearse 1973; Wild and Ames 1974; Miller et al. 1975; Stephenson 1977; Hines and Pearse 1982; Garshelis 1983; Estes and VanBlaricom 1985; Wendell et al. 1986). In general, otters are thought to invade a new area, rapidly consume the largest individuals of the most calorically rich prey, and then switch to smaller and less desirable prey as the preferred species become scarce (Ebert 1968; Wild and Ames 1974; Estes and Palmisano 1974; Ostfeld 1982; Riedman and Estes, this Vol.) or inaccessible (Lowry and Pearse 1973; Hines and Pearse 1982). Along rocky shores, the depletion of herbivorous prey like sea urchins and abalone (Estes and Palmisano 1974; Wild and Ames 1974; Estes et al. 1978) is followed by an increase in the cover of kelp forests and in the species richness of fishes (Estes and Palmisano 1974; Dayton 1975; Simenstad et al. 1978; Duggins 1980). Although sea otters may not play this role in all kelp forests (see Foster and Schiel, and Estes and Harrold, this Vol.), they clearly have a dramatic effect on some kelp forest communities (Estes and Palmisano 1974; Estes et al. 1978; Duggins 1980). In addition to rocky habitats, sea otters also forage in large areas of soft sediment (Calkins 1978; Kenyon 1969; Wild and Ames 1974; Miller et al. 1975; Stephenson 1977; Estes et al. 1981; Garshelis 1983; Estes and VanBlaricom 1985; VanBlaricom, this Vol.), where their effects on prey populations and community structure are quite different. Compared to the rocky shore, there is little information on the foraging habits and community role of sea otters in soft-sediment environments.