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Marine Mammal Physiology: Requisites for Ocean Living
6.4.1.1 Traditional methods
Analyses of food remains in regurgitates or scats of living animals or in the stomachs and
intestines of stranded animals have been the primary means for determining the diet and
resource partitioning of marine mammal species (Hindell et al. 1995; Lea et al. 2002; Field
et al. 2007). A particular disadvantage of stomach content and scat analysis is that they do
not provide any indication of dietary variations over the annual cycle of animals, as they
are restricted to the times of year animals are on-shore. For species which never come to
shore, this technique is only helpful in the relatively rare occurrence of gaining access
to specimens through misadventure (such as stranding) or through harvesting (such as
whaling).
These methods rely on the presence and identification of structures representative
of a typical meal, such as cephalopod jaws (commonly referred to as “beaks” due to
their resemblance to the beaks of parrots), fish bones, or fish otoliths. Cephalopod beaks
and fish otoliths are particularly useful diagnostic structures in the identification of
prey because their size and shape vary considerably from species to species (Figure 6.4).
Cephalopod beaks are composed of chitin and are not dissolved by digestive processes.
Figure 6.4 A schematic showing cephalopod jaws or “beaks” (left) and a fish ear stone (otolith;
right) and where they are in the intact animal. (Schematic by Indi Hodgson-Johnston.)