First evaluation of quantitative fatty acid signature analysis (QFASA) in dolphins

Abstract

Accurate diet estimation of marine mammals is fundamental to investigate their ecological roles in marine habitats, but it remains a pervasive challenge to researchers due to the constraints associated with conventional methods based on stomach contents or feces analysis, which are imprecise, limited to last meal and often biased. Quantitative fatty acid signature analysis (QFASA), an emerging method for diet estimations, has been demonstrated to be reliable in reconstructing long-term diets of many marine mammal predators; however, its application has not been seriously evaluated in dolphins. To this end, we compared the QFASA estimates obtained using 8 pre-existing calibration coefficient sets, 3 fatty acid subsets, and 3 prey library subsets to the true diet of a captive Indo-Pacific humpback dolphin (Sousa chinensis) that was fed a long-term diet of mostly gizzard shad (Clupanodon thrissa) with smaller proportions of Japanese seabass (Lateolabrax japonicus), pumpkinseed (Lepomis gibbosus), roughscale tonguesole (Cynoglossus lida), and Chinese herring (Ilisha elongate). The diet of the dolphin was best reconstructed using the calibration coefficients derived from captive feeding trials of American mink (Mustela vison) that were fed herring with the “main” fatty acid subset; this process correctly identified gizzard shad as the main prey source of the dolphin with the highest actual diet proportions and lowest predator signature proportions outside the range of the mean prey proportions. In addition, high accuracy and consistency were acquired in the diet estimations obtained using the calibration coefficients derived from minks fed herring and herring plus seal oil even though pseudo-prey were included in our model, revealing the high robustness and reliability of QFASA in reconstructing the dolphin diet. We recommend caution in selecting fatty acid subsets when using fatty acid signatures derived from different studies. Overall, QFASA offers a promising tool to quantify the long-term diets of humpback dolphins and other odontocetes.