Digestive efficiency and dry-matter digestibility in Steller sea lions fedherring, pollock, squid, and salmon

Dry-matter digestibility and energy digestive efficiency were measured in s ix juvenile Steller sea lions (Eumetopias jubatus) fed three diets each con sisting of a single species: herring, pollock, and squid. Two of the animal s were also fed pink salmon. Dry-matter digestibility (DMD) and digestive e fficiency (DE) were measured using the energy and manganese concentration i n fecal and food samples. DE values were high for all prey species (herring : 95.4 +/- 0.7% (mean +/- SD), pollock: 93.9 +/- 1.4%, salmon: 93.4 +/- 0.5 %, squid: 90.4 +/- 1.3%). Steller sea lions appear to digest prey of high e nergy density more efficiently than prey of low energy density. DMD values were also high for all prey species (herring: 90.1 +/- 1.8%, pollock: 86.5 +/- 3.4%, salmon: 87.3% +/- 2.6, squid: 90.5 +/- 1.2%). The low DMD value f or pollock compared with herring and squid was due to the high proportion o f bony material in pollock. There was a strong linear relationship between DE and DMD for each prey type, but the terms cannot be used interchangeably . DE measures are more meaningful than DMD in conveying the energetic benef its derived by sea lions from different types of prey. Species-specific mea sures of the digestible energy obtained from an array of prey items are a n ecessary component in understanding the bioenergetic consequences of consum ing different prey species.