Utilisation of fishery waste by Kelp Gulls attending coastal trawl and longline vessels in northern Patagonia, Argentina

Abstrakti

Utilisation of fishery waste by Kelp Gulls was studied onboard trawl and longline vessels in Golfo San Matfas; Patagonia, Argentina, betweenNovember 1996 and May 1997. Individuals of all age-classes were present in all counts and in similar proportions in both fisheries, although flocks consisted mainly of adults . Mean maximum number per day was significantly larger in the trawl than in the longline fishery (299.2 vs 197.6). In both fisheries, the number of gulls increased as the fishing operation progressed, with maximum numbers observed during discarding and/or gutting. Kelp Gulls consumed a fraction (67.0%) of the experimental discards as they selected prey according to species, size and shape. The Argentine Hake (Merluccius hubbsi) was the preferred fish . Longtail Hake (Macruronus magellanicus), Sea Salmon (Pseudopercis semifasciata) and flounders (Paralictchys isosceles and Xystreurys rasile) were negatively selected . Rejected species were deep bodied with respect to their length, had strong dorsal fin spines, were flat shaped or had caudal spines, making them more difficult to handle and swallow. The proportion of fish consumed for all species decreased with increasing fish length . Kelp Gull selection of discards according to species and size suggests that care should be taken when evaluating the availability of this food source for seabirds . Considering the fraction of fishery waste consumed by gulls obtained in this study, fish discards produced by coastal fisheries at Golfo San Matfas may support apopulation of more than 30 000 Kelp Gulls. This abundant and high quality food source could have an important effect on the population expansion of the Kelp Gull.