Age-0 Walleye Diet Shift Reflects Food Web Changes in Western Lake Erie

摘要

Walleye (Stizostedion vitreum) is an ecologically, economically, and recreationally important fish species in Lake Erie that fluctuates in recruitment each year. Walleye recruitment into adulthood is dependent on their growth and survival, which is directly affected by their diet during the first year of life. In the last few decades, Lake Erie has experienced several unintentional introductions of aquatic invasive species (AIS) that have likely led to environmental and food web changes, potentially impacting age-0 walleye diet and growth. To determine how the diet of age-0 walleye has changed in western Lake Erie, we compared diet composition between 2019 (new) and1994 (historical) fish during late spring, summer, and early fall. We found that during late spring (pelagic larval stage), cyclopoid copepods dominated diets in 2019, which differed from 1994 when calanoid copepods dominated diets. From summer to early fall (demersal juvenile stage), we found that large cladoceran species and benthic invertebrates made up a large portion of diets in 2019, which differed from 1994 when fish prey comprised almost all of the diets. Additionally, two of the most recent AIS, the spiny water flea (Bythotrephes longimanus) and round goby (Neogobius melanostomus), were found in 2019 diets, suggesting that age-0 walleye are adapting to the changing food web by incorporating new prey items into their diets. Our results also suggest that zooplankton and benthic invertebrates have become important prey items for age-0 walleye in Lake Erie in the later summer and fall months. Consequently, age-0 walleye by the end of their first growing season were smaller in 2019 compared to 1994 walleye. Switching to diets dominated by smaller non-fish prey during late summer and fall months could explain why walleye were smaller in 2019 and may have implications for walleye survival and recruitment into adulthood. Continued future analysis of age-0 walleye diet would provide confirmation on whether contemporary diets consistently contain less fish prey and more invertebrates and AIS because of food web changes or because of other complicating factors. In addition, it could be beneficial to compare how young walleye are adapting to a changing food web in Lake Erie, a eutrophic system, to young walleye in less productive systems.