Applying the Bayesian mixing model MixSIAR to fatty acid and stable isotope data to estimate diet of Antarctic seals

ALICIA I GUERRERO; ANNIE PINNOC; JAVIER NEGRETE; TRACEY L. ROGERS

Conferencia; XI Conferencia Internacional sobre la Aplicación de Isótopos Estables a Estudios Ecológicos; 2018

The combined use of fatty acids (FAs) and stableisotopes (SIs) has been recommended to accurately estimate diet composition.However, FA analysis has mainly been applied as a qualitative rather than aquantitative tool. Recently, efforts have concentrated on developing robustbiotracer-based quantitative methods to obtain accurate estimates of diet.Bayesian mixing model approaches were originally developed using SIs; however,they can be applied to any mixing process and be easily adapted for newvariables; therefore, it may be a powerful framework for estimating predatordiets using other types of data, such as FAs. The purpose of this study was toapply the quantitative Bayesian mixing model MixSIAR to both FA and SI data toevaluate how these two biochemical methods can be used complementarily to inferdiet. We estimated diet in three sympatric Antarctic seals: the leopard seal, Hydrurgaleptonyx; the crabeater seal, Lobodon carcinophaga; and the Weddellseal, Leptonychotes weddellii; using FAs from their blubber and SIs fromtheir whiskers. Samples from a total of 54 seals were collected during theaustral summer of 2015, off the Western Antarctic Peninsula. Overall, FA- andSI-based predictions were similar. Using both techniques, crabeater seals werefound to consume almost exclusively krill, leopard seals were also estimated tofeed mainly on krill, and Weddell seals diet was inferred to be dominated byfish. Due to FAs having more variables than SIs, it was possible todiscriminate between species. For example, we used 3 fish species as potentialprey of Weddell seals; the FA-based analysis determined that the notothenid Pleurogrammaantarcticum was the main prey followed by Notothenia coriiceps,whereas the myctophid fish Electrona antarctica was virtually absent.However, with SI data fish species had very similar isotopic values and hencehad to be combined into a single group, making it difficult to estimate diet tospecies level. Similarly, FA-based analysis estimated that crabeater seals notonly consume Euphausia superba but also other krill species. Werecommend the use of MixSIAR for FA data and encourage the use of both FA andSI analyses as complementary methods to obtain better taxonomic resolution.