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N.S. proposes using pesticide to kill invasive smallmouth bass in St. Marys River

The department captured illegally placed smallmouth bass in Piper Lake in July last year during routine sampling

October 2, 2020  The Canadian Press

HALIFAX — Nova Scotia is proposing to use pesticides for the first time in the battle against an invasive species of bass in the St. Marys River watershed.

The Department of Fisheries and Aquaculture said it’s filed applications with the province and the federal government to use the pesticide rotenone to eradicate the smallmouth bass in a headwater lake that flows into the St. Marys River system.

With federal and provincial approval, Jason LeBlanc said the department is aiming to have the pesticide in the small lake by mid-October.

LeBlanc, the manager of resource management at the fisheries and aquaculture department, said fish often become the dominant predator when they spawn in new waters, overtaking native species.

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The department captured illegally placed smallmouth bass in Piper Lake in July last year during routine sampling. The lake, in Pictou County, is fairly small, LeBlanc said. It’s five-hectares wide and three meters at its deepest point.

Rotenone, which targets fish gills and inhibits their breathing, will be able to kill the invasive bass, but will also kill other fish species in the lake, including yellow perch and a few different minnow species, LeBlanc said. The plan is to sacrifice the other species in the lake to prevent the bass from spreading.

To combat the fish’s growing population, officials previously used electrofishing, angling and lowered the water volume of the lake, but those efforts failed.

He said mechanical approaches are relatively effective in controlling fish numbers but not at eradicating a population, which is why the department has resorted to using the pesticide.

“In other watersheds throughout the province where smallmouth bass have been established, they became the dominant fish species to the demise, in some cases, of native fish species like brook trout which are very sensitive to predation and competition,” LeBlanc said in a recent interview.

He said the department is also concerned with maintaining the Atlantic salmon population, which could be threatened if the bass get further into the watershed.

Atlantic salmon and brook trout make for “nice, soft bodied, prefect bass food,” according University of Toronto professor Nicholas Mandrak.

Mandrak, who has done research on controlling invasive species, said smallmouth bass adapt well to new waters.

“They definitely appear to have significant impacts in ecosystems in which they’re not native,” he said in a recent interview. “They’re a relatively large … fish eater and also eat invertebrates and as a result are likely to consume native fish and invertebrate species when introduced into a lake.”

Mandrak said climate change has played a part in the growth of the smallmouth bass population in Canada since the fish tend to do better in warmer water. The naivete of other fish makes them perfect prey, he added.

“One of the reasons they have such strong negative impacts is because they’re being put into systems with species that have never encountered them before and, as a result, don’t know to flee from them.”

Smallmouth bass have had a long history in Nova Scotia, LeBlanc said. They were introduced to the province legally in the 1940s to start sport fisheries. Anglers have since spread them to other places to continue fishing for them, he added.

The desire to maintain the fish for recreational purposes has been a large part of their continued growth in the country, Mandrak said. “As soon as humans start valuing invasive species we go from managing against them to managing for them,.”

Educating anglers on the problems with bringing in smallmouth bass has been a part of the work of the Mersey Tobeatic Research Institute, a non-profit organization dedicated to maintaining biodiversity in southwestern Nova Scotia.

Thomas Sweeney, an aquatic researcher at the institute and an avid fisher, said the fish are particularly attractive to sport fishers because of their lively natures.

“They are very acrobatic for people who aren’t necessarily interested in food fish but hoping to catch and release,” he said in a recent interview.

“On a small fly rod, they jump out of the water multiple times, they’re very energetic. Simply put, they’re really fun.”

Sweeney echoed LeBlanc’s concern, saying smallmouth bass are difficult to get rid of once they’ve gone through a few mating cycles in a new location. His institute is keeping an eye on Nova Scotia’s proposed use of rotenone see whether or not its possible to eradicate the fish once they’ve settled into non-native waters.

By Danielle Edwards