An Enema Technique to Collect Dietary Information from Northern Fur Seals (<I>Callorhinus ursinus</I>) at Sea

Abstract

An enema technique was developed to obtain dietary information on northern fur seals (Callorhinus ursinus) at sea. The enema apparatus consisted of a hand pump and a soft PVC tube connected to a plastic tank filled with seawater. The tube was inserted into the fur seal’s anus, and fecal samples flushed out into a polyethylene bag enveloping the posterior of the fur seal. The efficacy of the enema sampling was tested on 23 fur seals captured and killed off the Pacific coast of northern Japan in April 1998. Twenty of 23 enema samples contained hard prey items such as fish otoliths and squid beaks. The average number (+ SD) of hard prey items retrieved from the whole large intestine was 26.9 + 33.0% for fish otoliths, 37.3 + 38.5% for squid upper beaks, and 43.3 + 40.9% for squid lower beaks. Size distributions of these prey items retrieved from the enema samples were similar to that remaining in the large intestines. These results indicated that the enema technique could provide dietary information that is comparable to intestinal contents and scat analysis. Combination of the enema technique with a pelagic live capture method using gillnets could provide a nondestructive way to investigate the feeding ecology of individual fur seals migrating offshore.