Trophic relationships in a seabird assemblage associated with fisheries at the Patagonian Continental Shelf.

SECO PON, J. P.; COPELLO S.; MARIANO-JELICICH, R.; FAVERO, M.

Viña del Mar

Conferencia; 11th International Conference on the application of Stable Isotopes Techniques to Ecological Studies; 2018

Overlap in diets and intra- and interspecific competition for food might influence the evolution of species and communities. This is also predicted for seabirds and so, seabird species within a community are expected to have distinct trophic niches. However, the interaction with fisheries and the potential exploitation of discards and/or fishery waste provides an alternative scenario that could be quite distinct from natural sources of food. Here we compared the trophic niche of a seabird assemblage associated with fisheries operating in the Patagonian Continental Shelf. We measured carbon and nitrogen stable isotopes in whole blood (n=72) and pectoral muscle (n=12)) of seabirds from the offshore wintering community of Procellariformes. Samples of Thalassarche melanophrys (BBA), Procellaria aequinoctialis (WChP), Daption capense (CP), Ardenna gravis (GSH), A. grisea (SSH) and Oceanites oceanicus (WSP) were obtained from birds captured onboard vessels or sampled from bycaught birds during austral winter 2011-2013. The quantitative method Stable Isotope Bayesian Ellipses in R (SIBER) was used to compute the area of the Bayesian ellipses and the overlap of the isotopic niches. Overall isotopic differences were observed (PseudoF5, 78= 28.4, P < 0.001), mainly due to larger values in WChP and BBA compared to other species.. Narrower isotopic niches were observed for BBA (SEAb = 0.96?2, CrI=0.7-1.32?2 ) and WChP (SEAb = 0.83?2 , CrI= 0.32-2.35?2) with large overlap between them (0.63?2). GSH also showed narrow isotopic niche (SEAb = 1.15?2, CrI= 0.50-2.41?2) but no overlap was observed with other species except to its congener. Wider niches observed in both SSH (SEAb = 54?2) and CP (SEAb = 4?2) is probably reflecting a variable use of different waters masses (i.e. from antartic to subtropical areas). BBA and WChP both feed by surface seizing but have different diving capacity . Moreover, diet composition of these two species is known to differ, at least during the breeding season. Our results show both species consuming prey from similar trophic level and associated to waters from the Patagonian Continental Shelf. These overlap in isotopic niche could be, at least in part, a product of the exploitation of feeding resources facilitated by the fishery industry.