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

MARINAO, C.; SUÁREZ, N.; YORIO, P.

Ciudad del Cabo

Congreso; II World Seabird Conference; 2015

Knowledge of seabird diets not only contributes to theunderstanding of predator-prey relationships but also provides information to assesstheir interaction with fishing activities. We comparatively assessed the typeand size of prey delivered to chicks at a mixed-species colony of Royal Terns (Thalasseus maximus maximus) and CayenneTerns (Thalasseus sandvicensiseurygnathus) at the Bahía San Blas marine protected area, Argentina. Thisarea is the site of one of the mainshore-based marine recreational fisheries of the southwestern Atlantic coast, receivingover 40 thousand fishers per year, which targets several species includingsilversides (Odontesthes spp.). Inaddition, plans have been proposed to develop a silverside artisanal fisheryand a commercial trawl fishery targeting Argentine Anchovy (Engraulis anchoíta) operates in adjacentwaters. During 2013 and 2014, observations of prey delivered to chicks of RoyalTerns (n = 2463 and 1414, respectively) and Cayenne Terns (n= 2516 and 1747,respectively) were conducted during the young and old chick stages (<10 and>10 days of age, respectively). Royal and Cayenne terns fed on at least 15and 10 prey species, respectively. In both tern species, the main prey specieswere silversides and Anchovy. Silversides dominated their diet in all observationperiods (57.5-70.1%) except for the young chick stage in 2013 when Anchovy wasthe main prey (85.4 ? 78.4%). In both years, Royal Terns deliveredsignificantly larger prey than Cayenne Terns, and both species deliveredsignificantly larger prey during the old than the young chick stage. Royal andCayenne terns showed an important overlap in the use of prey species, althoughprey size may be an important factor determining food partitioning between thetwo species. Results suggest that the ecological needs of terns should beconsidered in coastal fisheries management and future planning of the Bahía SanBlas marine protected area.