Abstract
Fishery damage caused by Great Cormorants Phalacrocorax carbo has recently become a critical issue in Japan. In our study, we identified the food habits of cormorant based on chick regurgitations, in Unoyama, Chita Peninsula, Aichi Prefecture, and from the stomach contents of legally shot cormorants at Yahagi River, Toyota, Aichi Prefecture. We examined whether the food habits of these two locations varied depending on cormorants' diet, and estimated the extent of damage to the Ayu Plecoglossus altivelis altivelis fishery based on stomach contents from the Yahagi sample, a location where concerns about Ayu fishery damage have arisen. Unoyama is located close to the coast, samples from there consisted mostly of coastal and brackish water fish species (96.5%), whereas the samples from the Yahagi River, which is located inland, were mostly composed of fluvial fish (98.5%). An index of relative importance for Ayu in the Yahagi sample ranked it 6th, and the species represented a wet weight percentage of just 5.18 %, suggesting that Ayu is relatively unimportant in the cormorant's diet. We recommend that in order to understand fishery damage by Great Cormorants it is necessary to estimate damage in each local area.
