Dreissenid-Induced Changes in the Feeding Habits, Depth Distribution, and Growth Rates of Lake Whitefish in the Great Lakes

The establishment of dreissenid mussels have contributed to the re-engineering of the Great Lakes ecosystem by altering trophic interactions. Commercially important lake whitefish, in particular, have shown declines in growth in several locations, and recent research indicates dreissenid-driven ecosystem changes may be the cause. Coinciding with the establishment of dreissenids, the primary food source of lake whitefish, Diporeia, has declined, which may be causing lake whitefish to search for new prey sources. Initial research in apopulation of lake whitefish in South Bay, Lake Huron, showed an increased dependence on nearshore food sources as a result. We analyzed ∂¹³C and ∂¹⁵N isotope ratios and growth rates over time from archived lake whitefish scale samples collected from several Great Lakes locations, to determine if there has been a wide-spread change in feeding patterns. We observed increases in ∂¹³C and decreases in ∂¹⁵N following dreissenid establishment, but no shift was observed in Lake Superior populations where dreissenids have not become established. The changes in isotopic signatures are indicative of a shift to nearshore food sources and a shallower depth distribution. Growth rate declines follow the changed diet source in these populations. These analyses indicate that dreissenids are influencing native Great Lakes fish communities.