Hakai Magazine

Coastal science and societies

smallmouth bass
Invasive smallmouth bass have taken hold in New Brunswick’s Miramichi Lake. Local groups worry the fish will start breeding in the nearby Miramichi River, which is vital to the region’s Atlantic salmon. Photo by RLS Photo/Alamy Stock Photo

Considering the Nuclear Option in Controlling Invasive Species

Rotenone: when you absolutely, positively have to kill every last fish in the lake.

Authored by

by Brian Owens

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How far would you go to get rid of an invasive species? In New Brunswick, conservation groups and local First Nations want to kill all of the fish in Miramichi Lake using a pesticide called rotenone. They want to reset the lake’s ecosystem, rid it of invasive smallmouth bass, and give the Miramichi River system’s dwindling Atlantic salmon a second chance.

The plan sounds drastic. But this nuclear option has been deployed before, says Barry Madison, an aquatic toxicologist at Queen’s University in Kingston, Ontario. “It’s really only used in oh-shit scenarios.”

Miramichi Lake has been in such a scenario for more than a decade, says Neville Crabbe, director of communications for the Atlantic Salmon Federation (ASF). Smallmouth bass were first reported in the lake in 2008, though they were present before that. The bass, which were likely introduced illegally by anglers, prey on juvenile salmon and trout, and compete for habitat and food with the native species.

The big fear is that the bass will move from the lake to the Miramichi River. In a 2009 report, Fisheries and Oceans Canada (DFO) said that the bass pose a high risk to the ecosystem and that “none of the consequences … will be positive for Atlantic salmon.”

So the North Shore Micmac District Council, along with ASF and other conservation groups, has asked the federal government for permission to eradicate the bass.

Rotenone, a naturally occurring poison made from the roots of tropical bean plants, has been used by Indigenous peoples around the Pacific Rim to catch fish for centuries, says Brian Finlayson, a rotenone expert from California who wrote the plan for its potential use in Miramichi Lake. The chemical is especially effective against fish and other gill-breathing animals because it can easily cross through the gills and into the bloodstream, where it disrupts oxygen use by the cells. Though fish are the target, rotenone would also take out most of the lake’s insects and amphibians as collateral damage.

Finlayson’s plan involves removing several species of native fish and amphibians from the lake and the tributaries leading into it, then using rotenone to kill everything left behind. Once the poison has dissipated, which should happen within a couple of weeks, the rescued fish and amphibians will be returned to the lake. The insects that are wiped out should naturally recolonize the lake fairly quickly, says Finlayson.

While it may sound extreme, an eradication project like this is not unheard of in Canada, says Joshua Kurek, a freshwater ecologist at Mount Allison University in New Brunswick. In 2001, rotenone was used to wipe out invasive chain pickerel in New Brunswick’s Despres Lake, also in the Miramichi watershed. It has also been used extensively in British Columbia’s Thompson River watershed. “It has a long track record of successful use,” says Kurek.

But rotenone is not always effective, and the ecosystem is not always restored to exactly how it was before the invasion. And sometimes, the eradication fails. In 2005, rotenone was used against invasive round goby in Pefferlaw Creek, in Ontario, to try to keep them out of Lake Simcoe. But the goby soon appeared in the lake anyway.

Crabbe says the rotenone plan is necessary because DFO’s efforts to contain and remove the bass from Miramichi Lake over the past decade have been ineffective. The department has been using a barrier to try to keep the bass out of the river, while trapping and removing them from the lake. But these techniques have not come close to eradicating the invaders. As a result, the bass have made it into the river, though, as yet, there is no evidence that they are spawning there.

The bass’s presence in the river will complicate efforts to eradicate them, Kurek says. In fact, it may now be too late. “They should have done this a long time ago,” he says.

On that point, Crabbe agrees. The group first submitted their plan to DFO in 2017, but so far has heard no response. The delay is “puzzling and frustrating,” says Crabbe. “This is a tragedy 10 years in the making,” he says, adding that “2008 should have been the oh-shit moment.”

The group hopes to put the plan into action in September 2020, but for that to happen they need a response from DFO soon. “We need answers this winter,” says Crabbe. “DFO’s actions now will determine the future of the Miramichi River.”

Likewise, DFO did not respond to multiple requests for comment for this article.