Great Cormorant (Phalacrocorax carbo) Science Article 21
Following the spectacular population increase in continental Cormorants, numbers of wintering birds on lakes and rivers in Bavaria, southern Germany, have risen sharply. Because of a growing concern among commercial fishermen and anglers, a diet study has been carried out at two major roosts: one at a lake (lake Chiemsee) and one at a dammed river (lower Inn river). Main prey species were cyprinids (Rudd, Roach, Chub and Bream), but at lake Chiemsee the commercially most important Whitefish also appeared in the diet during spawning in December/January. Mean daily intake per bird increased in the course of winter, because of larger specimens taken. Possible causes and effects of this phenomenon are discussed. Assuming an average daily uptake of 400 g fresh mass. it was estimated that at lake Chiemsee 3.3% of the total annual fish production was taken by Cormorants (vs. 28% by commercial fishermen). The total catch of Whitefish by Cormorants amounted to a mere 3.2% of the total commercial catch of this species. Larger proportions were scored for Eel (22.3%) and Pike (6.2%). At the lower Inn river it was estimated that Cormorants took 21% of the total annual fish production. Both in view of species composition in the Cormorants’ diet and of the consumption estimates specified above, it is considered unlikely that the birds impose a serious threat to commercial fisheries. Interference with recreational angling (e.g. for Grayling) may, however, occur.
Keller T., ARDEA 83 (1): 185-192