Interpreting Predator – Prey Interactions in Cayuga Lake Fishes Using Fatty Acid Signature Analysis

Fatty acids are transferred from prey to predator and can be used to assess trophic interactions in aquatic food webs. Therefore, to better understand Cayuga Lake food web dynamics, fatty acid signatures (FAS) of lake trout (Salvelinus namaycush) were compared to two major prey species in the lake; alewife (Alosa pseudoharengus) and round goby (Neogobius melanostomus). The main objectives of the study were to assess FAS dissimilarity between prey species and then compare each prey FAS to lake trout FAS. Fish were collected in 2014 and 2015 using seine nets (alewife, n = 255 and round goby, n = 448) and gillnets (lake trout, n = 60). Mean total lipid content in alewife was significantly higher than round goby (5.7 vs. 3.1%, Mann-Whitney U test = 19.666, df = 1, P \u3c 0.05). The FAS of both prey species differed significantly (ANOSIM, overall R = 0.594; P \u3c 0.05); concentration of 18:1n-9 was highest in alewife, whereas 22:6n-3, 20:5n-3, 16:1n-7, and 18:3n-3 concentrations were highest in round goby. Intraspecies (spatio-temporal) FAS variations were found for each prey species, but these variations were less significant than those observed between species. Although round goby in lake trout diet appeared to increase in 2015, comparisons of FAS of lake trout and both prey species suggest that lake trout diet is composed primarily of alewife