Fatty acid signatures and stomach contents of four sympatric<scp>L</scp>ake<scp>T</scp>rout: assessment of trophic patterns among morphotypes in<scp>G</scp>reat<scp>B</scp>ear<scp>L</scp>ake

Abstract

Abstract Sympatric diversification in L ake T rout is generally linked to differences in habitat use (especially depth) as a result of foraging on different prey items. However, extensive sympatric divergence has taken place in the shallow waters (≤30 m) of G reat B ear L ake, with multiple L ake T rout morphs varying in head and fin characteristics. To investigate diet partitioning as a potential explanatory mechanism for this diversification, we assessed trophic characteristics and relationships among four sympatric shallow‐water morphs of L ake T rout via analyses of fatty acids and stomach contents. Fatty acids and stomach contents both identified L ake T rout, C isco and M ysis as key prey items in L ake T rout diets. Interestingly, terrestrial invertebrates were also seasonally important among morphs, reflecting temporal variability of available prey in this arctic lake. Some diet partitioning was observed among morphs; M orph 1 was characterised as a generalist, M orph 3 was more benthic‐oriented, and M orphs 2 and 4 were mainly pelagic feeders. Of the latter, M orph 4 was the most specialised, whereas M orph 2 exhibited alternative feeding tactics of benthic cannibalistic and pelagic piscivorous feeding. Our findings demonstrate that complementary dietary methods can elucidate habits of opportunistic feeders, a task that can often be problematic, given their complex and variable diets. Our results add new information and perspectives on the current model of L ake T rout differentiation, demonstrating niche partitioning based on benthic versus pelagic habitat use and generalist versus specialist feeding tactics.