Rotenone for exotic trout eradication: nontarget impacts on aquatic communities in a mountain lake

Beaulieu J, Trepanier-Leroux D, Fischer JM, Olson MH, Thibodeau S, Humphries S, Fraser DJ, Derry AM. 2021. Rotenone for exotic trout eradication: nontarget impacts on aquatic communities in a mountain lake. Lake Reserv Manage. XX:XXX-XXX. Rotenone is widely used in lake and reservoir management for the eradication of exotic fish. However, nontarget effects of rotenone on freshwater organisms such as zooplankton and macroinvertebrates are of concern because of the ecological importance of these organisms in aquatic food webs as a resource base for fish, especially when rotenone is applied to lakes prior to native fish reintroduction. The objective of our study was to determine the effects of rotenone on nontarget zooplankton and macroinvertebrate species assemblages in a headwater mountain lake where rotenone was applied to remove exotic brook trout (Salvelinus fontinalis; Banff, AB Canada). We found strong negative rotenone impacts on the community structure and density of crustacean zooplankton, and to a lesser extent on macroinvertebrates, lasting for at least 1 yr after the rotenone treatment. Our study offers 2 unique insights that differentiate from rotenone studies on other lakes: (1) the persistent and almost complete eradication of crustacean zooplankton in the following summers, 11 months after rotenone treatment, and (2) a considerable shift in the macroinvertebrate community composition, likely resulting from combined effects of both nontarget rotenone effects on taxon density and trophic interactions associated with the eradication of brook trout from the lake. We advocate that assisted recolonization in the restoration of aquatic food webs could play an important role in facilitating nontarget aquatic community recovery following lake rotenone treatment.

Automated summary

This study demonstrates the negative impacts of rotenone on crustacean zooplankton and macroinvertebrate species in a mountain lake, lasting for at least a year after treatment. Unique insights include almost complete eradication of crustacean zooplankton 11 months after rotenone treatment, and a considerable shift in macroinvertebrate community composition likely due to nontarget effects and trophic interactions associated with trout eradication. Assisted recolonization may play a crucial role in facilitating nontarget aquatic community recovery post-rotenone treatment.