Fatty Acids Differentiate Between Consumed Diets Despite Variation within Prey Species’ Profiles

Techniques that biochemically trace foraging habits of predators rely on the assumption that intra-specific variation in prey species is smaller than variation among them. At the same time, these techniques often show that diets can induce drastic changes in the biochemical profiles of prey species, especially across different ecosystems. We tested if intra-specific variation in fatty acid profiles of prey species added enough “noise” to confound quantitative fatty acid signature analysis (QFASA) using a controlled feeding experiment. Steelhead trout (Oncorhynchus mykiss) were fed either alewife (Alosa pseudoharengus) or round goby (Neogobius melanostomus) from either Lake Ontario or Cayuga Lake for a period of 8 weeks. Fatty acid profiles were significantly different between prey species and between lake of origin within each species. Differences in fatty acid profiles of steelhead trout strongly reflected the differences between prey species, whereas the differences related to prey source (lakes) were noted at a much lesser extent. QFASA performed remarkably well given the differences noted between the systems prey originated from. Our results indicate that QFASA models for steelhead trout are not specific to one lake, and could provide estimates for other freshwater systems where alewife and round goby serve as the primary forage.