DIFFERENCES BETWEEN COLONIES AND CHICK-REARING STAGES IN IMPERIAL CORMORANT (PHALACROCORAX ATRICEPS) DIET COMPOSITION: IMPLICATIONS FOR TROPHIC STUDIES AND MONITORING

CYNTHIA IBARRA; CRISTIAN MARINAO; NICOLÁS SUÁREZ; PABLO YORIO

WILSON JOURNAL OF ORNITHOLOGY

WILSON ORNITHOLOGICAL SOC

Año: 2017

1559-4491

We assessed differences in diet composition between Imperial Cormorants (Phalacrocorax atriceps) breeding at Isla Arce and Isla Vernacci Este, Golfo San Jorge, Argentina. Both colonies are located within the Patagonia Austral Marine Park and commercial trawl fisheries operate in adjacent waters, thus knowledge of their food requirement is fundamental to assess potential conflicts and monitor interactions. A total of 63 adult Imperial Cormorants were flushed during the chick rearing period in 2014, 32 at Isla Arce and 31 at Isla Vernacci Este. A total of 27 and 30 prey taxa were recorded in stomach samples at Isla Arce and Isla Vernacci Este, respectively, and at least 21 were common to both islands. Significant differences in diet composition in terms of importance by mass were found between young and old chick stages at Isla Arce but not at Isla Vernacci Este. Rockcods (Patagonotothen spp.) were dominant at Isla Vernacci Este during both chick stages (75.7 and 86.5%, respectively). At Isla Arce, rockcods, argentine anchovy (Engraulis anchoita) and argentine hake (Merluccius hubbsi) contributed similarly to their diet (26-33%) during the young chick stage, while argentine anchovy dominated during the old chick stage (76.6%). Diet composition in terms of importance by mass was significantly different between colonies. Imperial Cormorants consumed benthic, demersal and pelagic prey confirming their plasticity in feeding habits, but their contribution differed depending on the site and chick stage. Our results suggest that diet assessments and monitoring of the potential interaction between Imperial Cormorants and fisheries should not be based on information from a single breeding stage or location, but requires the analysis of diet composition throughout the breeding cycle with a representative sampling of the seventeen colonies within the marine park.