Diet variation in breeding Imperial Cormorants: implications for trophic studies and monitoring

IBARRA, C.; MARINAO, C.; SUÁREZ, N.; YORIO, P.

Puerto Iguazú

Congreso; Ornithological Congress of the Americas (XVII RAO/XXIV CBO/XCV AFO); 2017

Association of Field Ornithologists, Sociedade Brasileira de Ornitologia y Aves Argentinas

Differences in diet composition were assessed between ImperialCormorants (Phalacrocorax atriceps) breeding at Isla Arce and IslaVernacci Este, Golfo San Jorge, Argentina. Both colonies are located within thePatagonia Austral Marine Park and important commercial trawl fisheries operatein adjacent waters, thus knowledge of their food requirement is fundamental toassess potential conflicts and monitor interactions. Induced regurgitationswere obtained from 63 breeding adults, 32 at Isla Arce and 31 at Isla VernacciEste, during two stages of their chick rearing period in the breeding season2014. A total of 27 prey taxa were recorded in stomach samples at Isla Arce and30 at Isla Vernacci Este, and at least 21 were common to both islands.Significant differences in diet composition in terms of importance by mass werefound between colonies. In addition, significant differences were found betweenthe young and old chick stages at Isla Arce but not at Isla Vernacci Este. ImperialCormorants consumed benthic, demersal and pelagic prey confirming theirplasticity in feeding habits, but their contribution differed depending on thesite and chick stage. Results suggest that diet assessments and monitoring ofthe potential interaction between Imperial Cormorants and fisheries cannot bebased on information from a single breeding stage or location, but requires theanalysis of diet composition throughout the breeding cycle at a representativesample of the 17 colonies within the marine park.