Estimación de dieta de focas antárticas usando la herramienta Bayesiana MixSIAR con ácidos grasos e isótopos estables.

GUERRERO ALICIA ISABEL; PINNOCK ANNIE; NEGRETE JAVIER ; ROGERS TRACEY L

Congreso; XII Congreso de la Sociedad Latinoamericana de Especialistas en Mamíferos Acuáticos; 2018

The combined use of fatty acids (FAs) and stable isotopes (SIs) has been recommended to accurately estimate diet composition. However, FA analysis has mainly been applied as a qualitative rather than a quantitative tool. Recently, efforts have concentrated on developing robust biotracer-based quantitative methods to obtain accurate estimates of a predator?s diet. Bayesian mixing model approaches were originally developed for SIs; however, they can be applied toany mixing process and be easily adapted for new variables; therefore, it may be a powerful framework for estimating predator diets using other types of data, such as FAs. The purpose of this study was to apply the quantitative Bayesian tool MixSIAR to both FA and SI data to evaluate how these two biochemical methods can be used complementarily to infer diet. We estimated diet in three sympatric Antarctic seals: the leopard seal, Hydrurga leptonyx; the crabeater seal, Lobodon carcinophaga; and the Weddell seal, Leptonychotes weddellii; using FAs from their blubber and SIs from their whiskers. Samples from a total of 54 seals were collected during the austral summer of 2015, off the Western Antarctic Peninsula. Overall, FA- and SI-based predictions were similar. Using both techniques, crabeater seals were found to consume almost exclusively krill; leopard seals were also estimated to feed mainly on krill; and Weddell sealsdiet was inferred to be dominated by fish. Due to FAs having more variables than SIs, it was possible to discriminate between prey species. For example, we used 3 fish species as potential prey of Weddell seals, the FA-based analysis determined that Pleurogramma antarcticum was the main prey followed by the myctophid Electrona antarctica, which coincides with published scat content studies. However, with SI data fish species had very similar isotopic values and hence had to be combined into a single group, making it difficult to estimate diet to species level. Similarly, FAbased analysis estimated that crabeater seals not only consume Euphausia superba but also other krill species. We recommend the use of MixSIAR for FA data and encourage the use of both FA and SI analyses as complementary methods to obtain better taxonomic resolution.