Dietary analysis of the emerald shiner (Notropis atherinoides) in the Upper Niagara River using fatty acids, stomach contents, and stable isotopes

Describing ontogenetic and temporal shifts in diet is a fundamental step in understanding food web structure in any ecological community. I conducted a dietary analysis of the emerald shiner (Notropis atherinoides), a keystone species in the Niagara River (NY), using a detailed analysis of fatty acids combined with data on stomach contents and stable isotopes. For both 2014 and 2015, oleic acid and DHA were important fatty acids responsible for the majority of the differences among groups. There was a seasonal shift in fatty acids from relatively high levels of 22:5n-6 and DHA early in the season to increased levels of EPA and 18:3n-3 later in the season. Smaller shiners had lower values of EPA, DHA, and oleic acid and higher values of 18:2n-6 compared to large shiners. Multivariate statistical analysis showed that emerald shiners had approximately 80% similarity in fatty acid composition across all size classes and seasons; despite this similarity, the analysis was able to differentiate among most groups of shiners. In general, the fatty acid results were consistent with data from stomach contents, which indicated that copepods were more important later in the season and were more common in the stomachs of large shiners. Stable isotope ratios of carbon and nitrogen indicated that all emerald shiners were eating at a similar trophic level. These results establish an important dietary baseline for the emerald shiner which will be useful in the future given the ongoing anthropogenic influences and habitat alterations that are occurring in the upper Niagara River