Can Fish Planktivores Exert Top-Down Control on the Lake Huron Mysid Population?

Mysis relicta is an important food web intermediary between phytoplankton, zooplankton, and fish and is likely a conduit for energy and nutrients between benthic and pelagic habitats.  With the decline of Diporeia sp. in the Great Lakes, Mysis is now the only large, high-lipid prey item available for many fish species.  A number of native and non-native fish have historically been heavily reliant on Mysis as prey, and efforts to reintroduce some native species could be hindered if availability of Mysis as prey is limited.  Recent efforts have shown that abundance of Mysis in Lake Huron is considerably lower than in other Great Lakes, but the cause for this difference is not clear.  While bottom-up and top-down influences are likely both important, we focused on estimating the magnitude of Mysis consumption by fish to determine if fish are exerting top-down control on the population.  We used seasonal Mysis abundance data, fish abundance data, and fish diet data from Lake Huron in 2007, along with bioenergetic modeling to estimate consumption of Mysis by fish and Mysis production.  Given trends observed in some Great Lakes Mysis populations as well as relatively low abundance in Lake Huron, this type of comparison is an important step in understanding the potential for reintroduction of native species that are reliant on Mysis as prey.