CONSUMPTION OF DISCARDS AND INTERACTIONS BETWEEN BLACK-BROWED ALBATROSS (Thalassarche melanophrys) AND KELP GULLS (Larus dominicanus) AT TRAWL FISHERIES IN GOLFO SAN JORGE, ARGENTINA

DIEGO GONZÁLEZ ZEVALLOS; PABLO YORIO

JOURNAL FUR ORNITHOLOGIE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2011 vol. 152 p. 827 - 838

0021-8375

We evaluated discard consumption by Kelp gulls (Larus dominicanus) and Black-browed Albatross (Thalassarche melanophrys) associated to trawlers operating at Golfo San Jorge, Argentina, and assessed differences in their feeding behavior, prey size preferences and foraging efficiency. Observations were made on-board hake (January 2007) and shrimp vessels (November 2008). The Kelp Gull and Black-browed albatross were the most frequent and abundant seabirds at both fisheries, while Argentine hake (Merluccius hubbsi) dominated the composition of discards. Kelp gulls and Black-browed Albatross consumed 91% of experimentally discarded hake (n = 1236). Mean size of prey consumed by gulls was 22.4 and 23.7cm in the hake and shrimp fisheries, respectively, while that of prey consumed by albatross was 28.5 and 31.3 cm, respectively. In both fisheries, gulls selected the smaller prey available (<25 and <30 cm in hake and shrimp fisheries, respectively) while Black-browed albatross selected the larger prey available (>25 and >30 cm in hake and shrimp fisheries, respectively). Intraspecific and interspecific kleptoparasitism were significantly more frequent than expected in Kelp gulls and Black-browed albatross, respectively. Robbing efficiency was clearly higher in albatross than gulls. In both species, sizes of prey consumed by direct capture were significantly smaller than those stolen, and the rate of kleptoparasitism increased with prey size. Gulls stole significantly smaller prey than albatross. Prey selection by Kelp gulls is affected by the interaction with Black-browed albatross, and the degree at which discards are used by both species appears to depend on the fishery considered, given differential food offer and selection of prey sizes according to seabird species-specific preferences.