Assessment of Compound-Specific Fatty Acid δ13C and δ2H Values to Track Fish Mobility in a Small Sub-alpine Catchment

Methods for identifying origin, movement, and foraging areas of animals are essential for understanding ecosystem connectivity, nutrient flows, and other ecological processes. Telemetric methods can provide detailed spatial coverage but are limited to a minimum body size of specimen for tagging. In recent years, stable isotopes have been increasingly used to track animal migration by linking landscape isotope patterns into movement (isoscapes). However, compared to telemetric methods, the spatial resolution of bulk stable isotopes is low. Here, we examined a novel approach by evaluating the use of compound-specific hydrogen and carbon stable isotopes of fatty acids (delta H-2(FA) and delta C-13(FA)) from fish liver, muscle, brain, and eye tissues for identifying site specificity in a 254 km(2) sub-alpine river catchment. We analyzed 208 fish (European bullhead, rainbow trout, and brown trout) collected in 2016 and 2018 at 15 different sites. delta(13)C(FA )values of these fish tissues correlated more among each other than those of delta(2)H(FA )values. Both delta H-2(FA) and delta(1) C-FA values showed tissue-dependent isotopic fractionation, while fish taxa had only small effects. The highest site specificity was for PC DHA values, while the delta H-2 isotopic difference between linoleic acid and alpha-linolenic acid resulted in the highest site specificity. Using linear discrimination analysis of FA isotope values, over 90% of fish could be assigned to their location of origin; however, the accuracy dropped to about 5696 when isotope data from 2016 were used to predict the sites for samples collected in 2018, suggesting temporal shifts in site specificity of delta H-2(FA) and delta C-13(FA). However, the predictive power of delta H-2(FA) and delta C-13(FA) over this time interval was still higher than site specificity of bulk tissue isotopes for a single time point. In summary, compound-specific isotope analysis of fatty acids may become a highly effective tool for assessing fine and large-scale movement and foraging areas of animals.

Automated summary

Methods for identifying animal origin, movement, and foraging areas are crucial for understanding ecological processes. This study examined the use of compound-specific stable isotopes of fatty acids to identify site specificity in a river catchment. The results showed that this method can be an effective tool for assessing the movement of animals and their specific foraging areas.