The Miramichi River and its fisheries provides sustenance and employment for thousands of people every year. A 2011 study found wild Atlantic salmon generate 630 full-time equivalent jobs and $16 million in annual spending for the region. The introduction of smallmouth bass in Miramichi Lake threatens Indigenous food, social, and ceremonial fisheries and a recreational fishery that draws people from around the world to New Brunswick every year.
In 2016, the Working Group on the Eradication of Smallmouth Bass from Miramichi Lake commissioned an expert report to assess the technical aspects and feasibility of restoring Miramichi Lake to its natural state. Brian Finlayson and Don Skaar of Fish Control Solutions and Michael R. can den Heuval of the Canadian Rivers Institute, University of Prince Edward Island, were engaged. In July 2017, the consultants delivered their final report.
Atlantic salmon is the most important fish species economically, recreationally, spiritually and ecologically in the Miramichi River watershed. The Miramichi has been recognized as the “mother of all salmon rivers”, reflecting the spectacular nature of this population. Unfortunately, due to low adult returns, Atlantic salmon in the Miramichi River are thought to be below population levels that are sustainable indefinitely.
The introduction of invasive smallmouth bass into Miramichi Lake was observed in 2008, the first and only known incidence of this species in the Miramichi River watershed. This introduction has caused significant concern with regards to the potential impacts of predation and competition with wild Atlantic salmon in the Miramichi. A previous scientific review judged the risk to salmon to be moderately high if smallmouth bass colonize the river, although the uncertainty regarding that prediction was also high.
Containment and control measures, including a temporary seasonally installed barrier and exhaustive fishing efforts, have been in place in Miramichi Lake since 2008. While populations of smallmouth bass are greatly reduced, these efforts have failed to eradicate the species and they have persisted in the lake up to the present day after a decade of control effort.
The general scientific consensus as established by multiple efforts at fish control around the world is that control efforts rarely if ever achieve eradication, and the efforts in Miramichi Lake support that contention. The only feasible method that has a high probability of smallmouth bass eradication in Miramichi Lake is the use of a piscicide, of which rotenone is the most widely used substance and the only piscicide registered for use in Canada.
The expert report describes a detailed plan for the application for rotenone, including limiting non-target species damage, monitoring, mitigation, and remediation to restore native species in the lake. The best timing window for the efficacious rotenone application, considering all factors including mitigation measures, is mid-September. An eradication effort using 0.075 mg/L rotenone is proposed and discussed along with proposed monitoring and mitigation involving removal, holding, and reintroduction of non-target species. The total costs of this eradication effort including the rotenone application, mitigation and monitoring would be approximately a million dollars. Such an action will require a substantial effort devoted to involving the public in the discussion of the relative risks and, the potential ecological and economic consequences (tradeoffs) of using rotenone versus doing nothing.