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

Abstract

Dry-matter digestibility and energy digestive efficiency were measured in six juvenile Steller sea lions (Eumetopias jubatus) fed three diets each consisting of a single species: herring, pollock, and squid. Two of the animals were also fed pink salmon. Dry-matter digestibility (DMD) and digestive efficiency (DE) were measured using the energy and manganese concentration in 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 energy 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 for pollock compared with herring and squid was due to the high proportion of bony material in pollock. There was a strong linear relationship between DE and DMD for each prey type, but the terms cannot be used interchange- ably. DE measures are more meaningful than DMD in conveying the energetic benefits derived by sea lions from dif- ferent types of prey. Species-specific measures of the digestible energy obtained from an array of prey items are a necessary component in understanding the bioenergetic consequences of consuming different prey species. Resume : Las digestibilite des matieres seches et l'efficacite de l'energie digestive ont ete mesurees chez six Otaries de Steller juveniles (Eumetopias jubatus) gardees a une diete monospecifique constituee de hareng, de goberge ou de calmar. Deux animaux ont aussi recu du Saumon rose en nourriture. La digestibilite des matieres seches (DMD) et