Chick provisioning by syntopic Royal and Cayenne terns at an important fishing ground in northern Patagonia

MARINAO, CRISTIAN JAVIER; SUÁREZ, NICOLÁS; YORIO, PABLO

Cape Town

Congreso; II World Seabirds Conference; 2015

World Seabird Union

Knowledge of seabird diets not only contributes to the understanding of predator-prey relationships but also provides information to assess their interaction with fishing activities. We comparatively assessed the type and size of prey delivered to chicks at a mixed-species colony of Royal Terns (Thalasseus maximus maximus) and Cayenne Terns (Thalasseus sandvicensis eurygnathus) at the Bahía San Blas marine protected area, Argentina. This area is the site of one of the main shore-based marine recreational fisheries of the southwestern Atlantic coast, receiving over 40 thousand fishers per year, which targets several species including silversides (Odontesthes spp.). In addition, plans have been proposed to develop a silverside artisanal fishery and a commercial trawl fishery targeting Argentine Anchovy (Engraulis anchoíta) operates in adjacent waters. During 2013 and 2014, observations of prey delivered to chicks of Royal Terns (n = 2463 and 1414, respectively) and Cayenne Terns (n= 2516 and 1747, respectively) were conducted during the young and old chick stages (10 days of age, respectively). Royal and Cayenne terns fed on at least 15 and 10 prey species, respectively. In both tern species, the main prey species were silversides and Anchovy. Silversides dominated their diet in all observation periods (57.5-70.1%) except for the young chick stage in 2013 when Anchovy was the main prey (85.4 ? 78.4%). In both years, Royal Terns delivered significantly larger prey than Cayenne Terns, and both species delivered significantly larger prey during the old than the young chick stage. Royal and Cayenne terns showed an important overlap in the use of prey species, although prey size may be an important factor determining food partitioning between the two species. Results suggest that the ecological needs of terns should be considered in coastal fisheries management and future planning of the Bahía San Blas marine protected area.