Isotopic evidence for trophic niche partitioning in historical Laurentian Great Lakes

Background/Question/Methods

Anthropogenic activities have dramatically impacted the Laurentian Great Lakes over the last century. By the 1960s, non-native species introductions, overfishing, habitat destruction, cultural eutrophication, and toxic discharges had produced a virtual food web collapse in each of the lakes. Extirpations of a diverse group of fish species, the deepwater coregonines (Coregonus spp.), have left vast areas of the Great Lakes barren and fisheries managers currently are considering rehabilitating the threatened populations. However, little is known about the historical ecology of the extirpated coregonines. We used stable isotope (δ¹³C, δ¹⁵N) analysis and museum-archived fish specimens to retrospectively investigate the historical ecological partitioning of the coregonines. We compared the food web structure of deepwater coregonines from contemporary Lake Nipigon and Lake Superior – potential source lakes – to Great Lakes populations from the early 1900s.
Results/Conclusions

Coregonine populations from all sample lakes (Michigan, Huron, Superior, Nipigon) exhibit significant isotopic niche partitioning among species, especially along a δ¹³C gradient. This δ¹³C gradient appears to correlate with preferred depth among species. Furthermore, the way in which the deepwater coregonines relate to one another in isotopic niche space was similar across lakes. This finding is particularly intriguing based on the morphological diversity of species from one lake to another. Our stable isotope analysis suggests that the distinct niches occupied by coregonines are consistent across lakes. While morphology may vary across lakes, the way in which species relate to one another, ecologically, does not. Understanding the ecological partitioning of deepwater coregonines lends important insight into the restoration potential of these threatened populations and may be useful for managers interested in restoring a diverse ecosystem.