Seasonal diet of eastern brook trout and the influence of lipid extraction on stable isotope analysis, Owhi Lake, WA

Amy Martin

Stable isotope analysis (SIA) for ecological research clarifies nutrition sources, trophic structure, competitive relationships, and habitat use. In order for SIA to be informative, sample collection and processing should address natural variation in carbon and nitrogen isotopes of primary consumers and upper trophic organisms. Variable concentration of lipid tissue, which is [delta]13C depleted compared to protein, can cause diet misinterpretations from liver and potentially muscle tissue. In addition, seasonal isotopic shifts of prey species can influence diet modeling results. A diet study on seasonal feeding habits of Eastern brook trout (Salvelinus fontinalis) in Owhi Lake, WA examined muscle and liver lipid content and seasonality of diet sources, two potentially influential factors in diet modeling. Gut content analysis (GCA) and SIA produced similar conclusions on prey importance to diet. Chironomids in May and June had high frequency of occurrence (FO) and percent by weight (PBW) representation, while littoral crayfish dominated FO and PBW between July and September. Zooplankton had high FO, but PBW always <1%. Proportional plots produced by Stable Isotope Analysis in R (SIAR) modeling suggested assimilation of predominately crayfish and littoral prey to liver tissue, and crayfish and chironomids to muscle. Inputting prey source values from spring favored crayfish proportionally, while summer prey values favored chironomids. Seasonality of [delta]13C and [delta]15N of invertebrate species influenced diet probability calculations by SIAR. Adjusting for lipids caused a mean [delta]13C enrichment of 0.9‰ and produced ecologically informative changes in May and July diet probability. Important shifts occurred in all months for liver tissue, suggesting greater nutritional importance of littoral crayfish than originally plotted. Relatively [delta]13C depleted chironomids were favored in analysis of untreated samples. Extracting lipids from May muscle and all liver tissue helped answer questions regarding habitat use between littoral and pelagic prey. This thesis is arranged into three sections. Chapter 1 is an introduction and literature review, Chapter 2 is organized to have the components of a publishable paper. Chapter 3 contains management suggestions for brook trout in Owhi Lake based on habitat use.

Seasonal diet of eastern brook trout and the influence of lipid extraction on stable isotope analysis, Owhi Lake, WA

Files and links (1)

Abstract

Metrics

Details