12 - Diet, Foraging Structures, and Strategies

Abstract

This chapter examines the diets of marine mammals, and several of the more obvious structural and behavioral specializations employed by marine mammals to capture their prey. The foraging energetics and the anatomy and physiology of digestion are also examined. Marine mammal diets and foraging strategies are direct consequences of the patterns of primary productivity, although most species prey on relatively large animals several trophic levels from the primary producers. Research on the foraging activities of marine mammals is difficult because feeding typically occurs below the sea surface. Standard approaches to analyzing foraging behavior, in addition to direct observations of predators pursuing and capturing prey, include stomach content analysis of dead, stranded, or net-entangled animals; stomach lavage of healthy restrainable animals; studies of fecal remains; and dietary patterns derived from stable isotope signatures in various tissues. The cheek teeth of pinnipeds and odontocetes are typically homodont with single pointed cusps adapted for feeding on fish and squid. Walruses employ a suction feeding strategy using the tongue as a piston to suck clams out of their shells. Tusks are used in social display rather than for feeding. The seasonal migration of the elephant seal, one of the best-studied feeding patterns among pinnipeds, involves an annual double migration with prolonged periods of offshore feeding. A specialized suction feeding strategy evolved independently in several pinniped lineages.