Lipid levels and diet compositions in lake charr ecotypes at Isle Royale in northern Lake Superior

Abstract

Lipid levels have been reported for lake charr Salvelinus namaycush ecotypes from Lake Superior, but have not been investigated for all four extant ecotypes concurrently in the same geographic area. In this study, a Distell fatmeter was used to measure lipid levels in the muscle in lean, humper, redfin, and siscowet lake charr collected seasonally during 2013 and 2014 on the north, east, and west sides of Isle Royale, Lake Superior from two depth strata: <80 and ≥80 m. Diet compositions and dietary similarity of lake charr were also measured. Differences in lipid level were analyzed by ANCOVA with length and age as covariates and ecotype, depth, sex, and season as factors. Lipid levels were found to be higher in lake charr inhabiting waters ≥80 m. In waters <80 m, mean lipid level was highest in large siscowets (≥703 mm; 41.2%) and lowest in old redfins (≥age 32; 11.8%). At depths ≥80 m, mean lipid levels were highest in large siscowets (64.4%) and lowest in young redfins (14.7%). In both depth strata, leans and humpers had intermediate lipid levels. Diet compositions were similar among ecotypes and did not explain the differences in lipid levels. Siscowets have the greatest depth range and vertical movement patterns among lake charr ecotypes in Lake Superior which is likely facilitated by high levels of intramuscular lipid. Lipid levels in leans and siscowets are heritable traits, but heritability of lipid levels in other ecotypes remains unknown.