Reclaiming Natural Systems and Native Fisheries through Chemical Restoration

Around the country, fisheries and wildlife management agencies are facing challenges including the loss of suitable and natural habitat for native fish through fragmentation, climate change impacts, and the spread of aquatic invasive species that outcompete, predate on, or in other ways negatively impact native fish populations. Aquatic invasive species are any species that is nonnative to a given waterbody and that has been deemed to cause ecological or economic harm to the system. Many aquatic invasive species, especially invasive fish, are impossible to fully remove through trapping, netting or other manual removal efforts. However, Maine Department of Inland Fisheries and Wildlife Fisheries Management Section has one effective option available that many states no longer have: chemical restoration. Chemical restoration allows the removal of all fish within a waterbody through the application of the chemical rotenone to the water, which when applied properly can effectively remove the aquatic invasive fish species.

What is rotenone?

Rotenone is a natural substance that is produced in the roots of certain tropical plants of the bean family and is acutely toxic to fish. Rotenone has a history of usage in the collection of food fish by people in Southeast Asia and Central and South America where those plants naturally occur. Rotenone has also been used in fisheries management for decades and is a safe alternative to other early fisheries management eradication products and techniques given the very low risk it poses to any terrestrial animals and its lack of environmental persistence. While many states have let go of their chemical restoration programs given the time and resources required for a reclamation project, the MDIFW Fisheries Management Section has maintained its program throughout the years as a way to reset natural systems and restore native fish populations that would otherwise be lost.

Chemical Restoration Projects in Maine

Maintaining this program is especially valuable given the coldwater fisheries in the state of Maine that have been saved and restored through chemical restoration projects. In recent years this has included restoration of Arctic charr populations, which do not exist as indigenous populations elsewhere in the lower 48, and the unique genetic compositions of both Arctic charr and other native salmonid populations. Reclamation is also available in response to the establishment of species of invasive fish that may be entirely new to the state and have the potential to cause irreparable damage to Maine's waters and fisheries if not eradicated. This can remove a "source population" (a population that has the potential to act as the origin of the spread of the species to other waters in the state) of a new species, limiting any further threat from the population to our waters quicker and more effectively than a manual removal (e.g., trapping and removing fish) effort would.  

Maine Department of Inland Fisheries and Wildlife has had several successful chemical restoration projects in the last couple decades to restore and protect native populations including Arctic charr in Big Reed Pond and Big Wadleigh Pond, and brook trout in Big Reed, Big Wadleigh, and Thissell Ponds. In 2023 the Department created a new Aquatic Invasive Species Coordinator Position, increasing the Fisheries Management Section's capacity to maintain the chemical restoration program as a tool for fisheries conservation. As aquatic invasive species continue to spread both to and within the state, the ability to use chemical restoration instead of relying solely on resource intensive and costly manual removal methods will likely save many of Maine's salmonid populations.