Spatial variability of lake trout diets in Lakes Huron and Michigan revealed by stomach content and fatty acid profiles

Abstract

Despite long-term efforts to restore lake trout (Salvelinus namaycush) populations in the Great Lakes, they continue to experience insufficient recruitment and rely on hatchery programs to sustain stocks. As lake trout reproductive success has been linked to diets, spatial heterogeneity in diet compositions is of interest. To assess spatial components of adult lake trout diets, we analyzed stomach contents and fatty acid profiles of dorsal muscle collected throughout Lake Michigan and along Lake Huron’s Michigan shoreline. Lake trout from Lake Huron were generally larger in both length and mass than those from Lake Michigan. However, lake trout from Lake Michigan varied more in size based on depth of capture with smaller fish being caught more in deeper set nets. Fatty acids and stomach contents indicated that alewife (Alosa pseudoharengus) were consumed more in western Lake Michigan in contrast with round goby (Neogobius melanostomus) along the eastern shoreline. Conversely, in Lake Huron, lake trout primarily consumed rainbow smelt (Osmerus mordax). These results indicate that diet compositions of lake trout populations are relatively plastic and offer new insights into within-basin heterogeneity of Great Lakes food webs.

Factors Affecting Postrelease Survival of Coded‐Wire‐Tagged Lake Trout in Lake Michigan at Four Historical Spawning Locations

“…), Lake Trout have diversified their diets to include Round Goby, which comprise 25–55% of Lake Trout diets in most regions of Lake Michigan during spring (Happel et al. ), potentially reducing the likelihood of TDC. Regardless of the mechanism, reduced Alewife abundance and the emergence of Lake Trout wild recruitment are correlated temporally (Riley et al.…”

“…; Turschak and Bootsma ; Happel et al. ; Luo et al ). Changes to Lake Trout diet have only recently been communicated, however, and stakeholder concerns and tensions among different management goals remain.…”

“…As Alewife biomass has declined to record-low levels in Lake Michigan since 2004(Madenjian et al 2018), Lake Trout have diversified their diets to include Round Goby, which comprise 25-55% of Lake Trout diets in most regions of Lake Michigan during spring (Happel et al 2018), potentially reducing the likelihood of TDC. Regardless of the mechanism, reduced Alewife abundance and the emergence of Lake Trout wild recruitment are correlated temporally (Riley et al 2011), and Lake Trout wild recruitment has increased substantially in Lake Huron since the Alewife population crashed there during 2002(Riley et al 2007He et al 2012).…”

“…However, recent findings demonstrate that Round Goby have become an important alternate prey for Lake Trout. The weight of the evidence suggests that Lake Trout diversify their diets to include more Round Goby when populations of Alewife and Rainbow Smelt are relatively low, while Pacific salmonines continue to rely predominantly on Alewife, thereby reducing diet overlap (Roseman et al 2014;Turschak and Bootsma 2015;Happel et al 2018;Luo et al 2019). Changes to Lake Trout diet have only recently been communicated, however, and stakeholder concerns and tensions among different management goals remain.…”

Fatty acids differentiate consumers despite variation within prey fatty acid profiles

“…Within published studies with lake trout we illustrate this by comparing a range of DHA proportions spanning 12.5% in lake trout that were fed invertebrates (Happel, Stratton, Pattridge, et al, 2016), to a reduction in the range of DHA values as lake trout shift from invertebrate diets to piscivory in L. Michigan (Happel et al, 2018), a range spanning 3.9% in adult lake trout caught in L. Ontario (Happel, Pattridge, Walsh, & Rinchard, 2017), and a range spanning 4.25% in the data presented herein on a species fed solely on fish prey items such as adult lake trout. Similar conclusions were made by Sushchik, Gladyshev, Kalachova, Makhutova, and Ageev (2006) when fatty acids of benthic prey and their predator, grayling (Thymallus arcticus), were compared.…”