Assimilation efficiency of captive ringed seals (Phoca hispida) fed different diets

Food type or quality can influence assimilation efficiency (AE). AE (digestibility of dry matter) of two captive adult ringed seals (Phoca hispida; one male, one female) was estimated for five prey types. In trials, each of >8 days duration, the seals were fed redfish (Sebastes spp.), capelin (Mallotus villosus), Arctic cod (Boreogadus saida), Atlantic herring (Clupea harengus) and a mixture of herring and shrimp (Pandalus borealis). Prey were marked so that faecal samples could be matched to individual seals, and AE was estimated by the relative concentration of Mn²⁺ in food and faeces. AE was high but varied among the prey species (redfish 83%; capelin 87%; Arctic cod 88%; herring 94%; herring/Pandalus mixture 92%). There was a weak, positive relationship between AE and prey lipid content or energy density, but a negative relationship with inorganic content. AE was lower than expected for cape lin with high fat content. AE was not correlated with meal mass, number of fish in a meal, or seal mass. AE did not differ between the two seals. Received: 30 September 1996 / Accepted: 28 December 1996