EVIDENCE OF SECONDARY CONSUMPTION OF FISH BY DOUBLE-CRESTED CORMORANTS

In 1993, we analyzed 742 regurgitant samples of nestling double-creste d cormorants Phalacrocorax auritus from 10 colonies in Penobscot Bay, Maine, USA. A total of 21 species of fish were identified from otolith s. Further, we recovered 15 fish stomachs from regurgitant samples 14 of which contained otoliths. We compared lengths of otoliths for a giv en taxon represented in both regurgitants and fish stomachs recovered from regurgitants, and found no significant difference. We concluded t hat otoliths occurring in regurgitant samples can result from secondar y consumption (i.e. the consumption of a prey fish containing otoliths in its stomach). Further, we caution that the use of otoliths in diet analyses of double-crested cormorants can inflate estimates of specie s percent occurrence and number.