Over the last 100 yr, anthropogenic stressors have decimated the assemblage of deepwater coregonines that once underpinned the food webs of the Laurentian Great Lakes. As a part of ongoing restoration efforts, fisheries managers are interested in reintroducing deepwater coregonines from remnant populations to reestablish historical food web connections. However, little is known about historical trophic position and niche partitioning among deepwater coregonines in the Great Lakes. We used nitrogen stable isotope analysis of amino acids to compare trophic position of museum-preserved (1920s) and present-day forage fishes in Lakes Michigan and Superior. In the 1920s, deepwater coregonines exhibited clear trophic niche partitioning, with trophic positions spanning a full trophic level. Additionally, species trophic positions were tightly conserved between lakes. In Lake Superior, trophic niche partitioning has been maintained over the last 100 yr, but trophic position has shifted downward by ∼0.5 trophic level. The more dramatic species loss in Lake Michigan corresponds with a sharp reduction in trophic niche breadth over time. Our study reveals remarkable trophic niche breadth among deepwater coregonines prior to the major anthropogenic impacts on the Laurentian Great Lakes and provides a food web benchmark for restoring the historical trophic diversity of this iconic species flock. Key words: compound-specific; Coregonus species; food webs; Lake Michigan; Lake Superior; museum specimens; niche partitioning; species reintroduction; stable isotopes; trophic compression.
Bibliographical noteFunding Information:
Stephanie Schmidt, David Bunnell, Patricia Arme-nio, Thomas Hrabik, and Ian Harding supplied samples used in this study. Prarthana Dharampal, Jonathan Pauli, Shawn Steffan, Scott Larson, Peggy Ostrom, Nathaniel Ostrom, Kaycee Morra, Alison Mikulyuk, Jake Walsh, Colin Smith, Tyler Tunney, Eric Pedersen, Martin Perales, and Daisuke Goto provided suggestions on earlier versions of the manuscript. This work was funded by the University of Wisconsin—Sea Grant (Federal Grants #HCE-7 and HCE-24 awarded to Jake Vander Zanden).
© 2018 Blanke et al.