Gut length, food transit time and diving habit in phocid seals

Abstract

The southern elephant seal (Mirounga leonina) has the ability to dive for 2 h and reach depths of 1200 m. This creature is also exceptional in having a small intestine that is 25 times body length. Krockenberger and Bryden advanced the hypothesis that the long small intestine has developed to compensate for the extended periods with reduced or even abolished intestinal blood perfusion during diving. To test this hypothesis we have measured small-intestinal lengths in crabeater (Lobodon carcinophagus), Weddell (Leptonychotes weddellii), Ross (Ommatophoca rossi), leopard (Hydrurga leptonyx), harp (Phoca groenlandica), ringed (Phoca hispida) and hooded (Cystophora cristata) seals and related them to available data on their maximal dive duration. We found no significant correlation (P > 0.05) between intestinal length relative to body length and diving ability, but we found that small-intestinal internal area was significantly (P 0.05) in response to repetitive diving over a period of 8 h. This indicates that the often-used Cr-EDTA is not a good measure for digesta passage time when used alone in seals, and that the hypothesis of Krockenberger and Bryden is most likely wrong.