VARIATION IN ASSIMILATION EFFICIENCY AND DIGESTIVE EFFICIENCY OF CAPTIVE HARP SEALS (PHOCA-GROENLANDICA) ON DIFFERENT DIETS

Digestive efficiency (DE) is influenced by many factors including food type or quality. Assimilation efficiency (AE) and DE of 12 captive ha rp seals (Phoca groenlandica) were estimated for five prey types in la rge outdoor seawater tanks. In trials of >9 days' duration, the seals were fed Atlantic cod (Gadus morhua), Arctic cod (Boreogadus saida), G reenland halibut (Reinhardtius hippoglossoides), Atlantic herring (Clu pen harengus), and capelin (Mallotus villosus). Fish were marked with inert tracers so that faecal samples could be matched to individual an imals. AE (digestibility of dry matter) was estimated from the relativ e concentration of Mn2+ in food and faeces. DE (digestible energy) was estimated from the relative concentrations of both Mn2+ and energy in food and faeces. AE and DE values were high, but varied among the fis h species (DE: Atlantic cod 93.5%; Arctic cod 93.5%; halibut 94.7%; ca pelin 95.7%; herring 96.6%). Both estimates of digestive efficiency we re positively correlated with prey energy density. For most prey, AE a nd DE were not correlated with meal size, number of prey in a meal, si ze of prey, or seal body mass. However, digestive efficiency was great er in seals fed smaller Atlantic cod, or meals of greater mass. Quanti fying estimates of digestive efficiency is important for formulating e nergy-based population consumption models, and so should be improved. It is recommended that more pinniped species be studied in captivity, that experiments last longer, and that the number of individuals studi ed be increased so that individual differences can be investigated.