Do cormorants injure fish without eating them? An underwater video study |
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Authors: | David Grémillet Manfred R Enstipp Maya Boudiffa He Liu |
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Institution: | (1) Centre d’Ecologie et Physiologie Energétiques, CNRS, 23 rue Becquerel, 67087 Strasbourg, France;(2) Present address: Giant Panda Research Center, Beijing Zoo, Beijing, China |
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Abstract: | The populations of European great cormorants (Phalacrocorax carbo) and North American double-crested cormorants (Phalacrocorax auritus) have increased sharply over the last decades and these piscivorous birds are suspected to deplete valuable fish stocks and
compete with human fisheries. Beyond direct consumption of fish, cormorants are accused of injuring vast numbers of prey without
eating them. Using underwater video systems, one of them mounted onto the back of tame Chinese cormorants, we evaluated the
proportion of successful pursuits of cormorants on live fish. Trials were conducted with 6 great cormorants and 9 double-crested
cormorants and involved a total of 676 prey pursuits. We show that, although they are regarded as highly efficient predators,
cormorants aborted about half of their pursuits. However, detailed analysis of prey-capture behaviour in double-crested cormorants
revealed that only 0.4% of the prey pursued was injured without being ingested. Further studies using miniature video systems
deployed on free-ranging cormorants are required to complement our knowledge of their hunting tactics. |
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