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Olrog’s gull interacting with fisheries in Argentina

Olrog’s gull (Larus atlanticus) is one of the six species of gulls worldwide that are considered threatened, in large part because there are only 2,300 breeding pairs restricted to 10 breeding colonies concentrating in two areas along the Argentina Patagonian coast. During the non-breeding season, the gulls migrate north to areas such as the nature reserve Mar Chiquita Lagoon in Buenos Aires Province, and where they have been observed relying heavily on the discards of recreational fishermen. The abundance of food has encouraged juvenile gulls especially to remain in wintering areas after adults return south to breed. Unfortunately, fishing discards are often entangled with hooks, fishing line, plastic bags and other materials that have led to Olrog gull mortality. The objectives of this projects were to: 1) describe the spatial and temporal distribution of Olrog gulls relative to recreational fishing activities at Mar Chiquita; 2) estimate the impact of recreational fishing on different age classes of gulls; 3) determine the degree of reliance on fishery discards by different age classes of gulls; 4) generate awareness among fishermen to promote behavior change with the aim of protecting Olrog gulls on their wintering grounds.

Beron and her team conducted point counts of juveniles, subadult and adult gulls at Mar Chiquita, monitoring behavioral interactions with fishing activity, and independently recorded information about the fishing activities themselves (type of fishing and fisherman behaviors). Diet and trophic analyses were conducted by collecting regurgitated pellets (often produced by birds and which contain prey hard parts allowing for prey identification) and by directly observing feeding events. Finally, posters and pamphlets were produced with information about Olrog gulls and distributed directly to fishermen during the peak gull season, providing an opportunity for discussion about the gulls’ situation. Posters were placed in local public areas where fishermen and other users of the reserve would most likely encounter them, and the researchers were able to get several articles published in the local media regarding the conservation status of and threats to the gulls.

Census data illustrated that gull abundance correlated directly with the abundance of recreational fishermen in the area, with subadults comprising the largest proportion of the gull population. Fifteen wounded gulls were identified over the course of the study, with limbs either entangled in fishing line or already amputated, presumably by previous entanglement. Diet analyses indicated that two species of local crab were the predominant prey sources for all age classes of gulls. However, gulls may only consume the flesh of some of the larger species of discarded recreational fishes, yielding no detectable hard parts. Additional methods such as stable isotope analyses could be employed in the future to further determine gull diets. Regardless, the predominance of crab in the diet was consistent with behavioral observations, suggesting that the Mar Chiquita gull population is not relying heavily on recreational fishing discards – an important finding suggesting that rates of entanglement may be contained while efforts continue to raise awareness about the impacts of abandoned fishing gear.