Modeling Lake Michigan's Suitability for Bigheaded Carps: The Importance of Diet Flexibility and Subsurface Habitat

Abstract

As Bighead and Silver Carp (bigheaded carps [BHC]) arrive at Lake Michigan’s doorstep, questions remain as to whether there is sufficient food for these invasive filter feeding fishes to grow and survive in the upper Great Lakes. Previous studies suggest that suitable BHC habitat in Lake Michigan is limited to a few productive, nearshore areas, but these studies have not considered how BHC’s diet plasticity or the availability of subsurface prey influences the ability of these fishes to grow in the lake. This study builds previous models by using simulated outputs of prey biomass (phytoplankton, zooplankton, and detritus) and water temperature from a three-dimensional biophysical model of Lake Michigan to evaluate growth rate potential (GRP, quantitative index of habitat suitability) of adult BHC throughout the entire volume of the lake. We defined suitable habitat as habitats that can support GRP ≥ 0 g∙g-1∙d-1. Consistent with previous studies, our results revealed that habitats with the highest quality were concentrated in eutrophic areas of Green Bay and other nearshore areas influenced by tributary phosphorous loads. However, in contrast to previous studies, we found suitable offshore habitat owing to our added consideration of BHC diet plasticity and subsurface prey resources. Feeding on all three types of prey throughout the water column extended suitable habitat throughout much of the lake for Bighead Carp, but not for Silver Carp. Our vertical analysis along the nearshore-offshore gradient near Muskegon, MI indicates that subsurface temperature and prey biomass are not only sufficient to support Bighead Carp growth, but provide maximum habitat quality during late summer stratification. Overall, our study demonstrates that BHC are capable of surviving and growing in much larger areas of Lake Michigan than predicted by previous studies, and thus indicates that the risk of establishment is not sufficiently mitigated by low plankton concentrations.