Gulf of Alaska | Mammals
Testing the accuracy of using fecal genetics to estimate pinniped diets Presenter: David Rosen , rosen@zoology.ubc.ca, University of British Columbia Chad Nordstrom , Chad.Nordstrom@dfo-mpo.gc.ca, Fisheries and Oceans, Canada Strahan Tucker , Strahan.Tucker@dfo-mpo.gc.ca, Fisheries and Oceans, Canada
Reconstructing the diets of top marine predators is essential for ecosystem-based management that protects environmental health while allowing economic development. Traditional techniques for describing diets of pinnipeds – such as identifying fecal hard part remains – are labour intensive, have known biases, and present challenges for quantifying relative intake of different species. Quantitative DNA metabarcoding has the potential to both accurately identify prey species in the diet of pinnipeds and better assess the relative intake of prey from DNA representation in the fecal samples. However, it is known that the relative frequency of genetic signatures in feces does not exactly match the proportion of food ingested, and may be affected by the type, proximate composition, and proportion of prey consumed. Therefore, this technique requires both refinement and calibration before consumption estimates can be applied with confidence in the field. We conducted controlled feeding experiments with 4 captive Steller sea lions fed known diets over 2-week intervals. Diets differed in the proportion of prey items offered (herring, coho salmon, capelin) that themselves differed in lipid content (9.3, 4.5, and 2.3%, respectively). DNA metabarcoding was used to quantify the relative genetic signatures derived from fecal samples, and these were analyzed in relation to known ingested food mass. Overall, uncorrected sequence counts over-estimated the consumption of herring (relative average +88%) and under-represented salmon (-55%) and capelin (-27%), with high variability between individual estimates. Application of previously published Tissue Correction Factors (TCF) which account for species-specific differences in the innate genetic signature (mitochondrial template DNA) density in the fish flesh and technical biases inherent in the sequencing process, significantly improved agreement between consumption estimates and fed diets (herring +17.4%, salmon -33.5%, capelin +18.4%). Some of the remaining differences in diet intake estimates are likely related to digestibility (which may also be related to lipid composition) and to fecal sample size, factors which are still under investigation. While this technique holds promise for quickly quantifying relative prey intake levels, further development under controlled experimental conditions is essential before it can be employed to estimate diets of wild pinnipeds.
Alaska Marine Science Symposium 2023 242
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