Effects of a trawling moratorium on the breeding success of the yellow-legged gull Larus cachinnans

  • Published source details Oro D., Bosch M. & Ruiz X. (1995) Effects of a trawling moratorium on the breeding success of the yellow-legged gull Larus cachinnans. Ibis, 137, 547-549.


During the 1993 and 1994 breeding seasons, a transect was established through the colony, which was surveyed once a day to establish the date of first hatching, clutch size and egg volume of a sample of nests (around 55 each year). In both years, a group of 14 nests were surrounded with 50 cm high netting just before hatching, to facilitate the location of chicks and monitoring of breeding success. The composition of chick diets was assessed based on analysis of regurgitates (of largely undigested food) produced by chicks when handled for ringing.

There was a significant difference in the composition of the diet of chicks between the two years, with the proportion of regurgitates containing marine fish (from fishing discards) falling from 48% to 12%, and the proportion containing prey items from rice fields, irrigation channels and lagoons increasing from 13% to 57%, between 1993 and 1994. Although average hatching date, clutch size, egg volume and hatching success did not differ significantly between the two breeding seasons, the fledging success of chicks was significantly lower during 1994 (22%) than during 1993 (47%).
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