Pesticide ‘last resort’ to eradicate invasive species: Rotenone used to eliminate smallmouth bass from Dobsons Lake

·4 min read

GUYSBOROUGH – After other efforts have been tried, a pesticide has been used to ensure the elimination of an invasive species from Dobsons Lake, near Half Island Cove.

In the spring of 2021, The Journal reported that smallmouth bass had been found in Dobsons Lake. The invasive species, if allowed to go unchecked, could outcompete naturally occurring trout and that’s why volunteers formed the Eastern Guysborough County Dobsons Lake/Cooeycoff Volunteer Association to address the situation.

That spring, fishing, both to remove the invasive species and gather data, was undertaken in the lake. Association volunteer John Dobson told The Journal at the time, “We’ll never fish them all out for sure.”

That’s why the association, in collaboration with the Nova Scotia Department of Fisheries and Aquaculture, sought to treat the lake with a pesticide called rotenone. Last weekend, on Sept. 10, the lake was treated with the chemical, which is meant to kill off the invasive species and allow for the successful reintroduction of trout in the lake.

Minister of Fisheries and Aquaculture Steve Craig said on Sept. 8, "We've seen the harm this invasive species has had on native fish communities in hundreds of lakes and waterways throughout Nova Scotia, where once strong populations of brook trout and other fish have been dramatically reduced or entirely eliminated by smallmouth bass … Rotenone is a measure of last resort, but it's one we know from experience works to protect our native fish species and the ecosystems that support them."

Before the decision to use rotenone was made, all other efforts were attempted – temporary barriers, targeted angling, and electrofishing – to corral and eliminate the smallmouth bass in the one lake which is linked to more than 25 lakes, ponds and streams in the area.

The Journal spoke with Mike Feltmate, a member of the volunteer association, on Sept. 12 to find out how the weekend application of rotenone proceeded on Dobsons Lake.

“It went extremely well,” said Feltmate, “It was well executed, extremely well planned by the [Department of Fisheries and Aquaculture] Inland Fisheries people and with the help of the volunteers [approximately 24] it went quiet smoothly, no hiccups whatsoever, just as planned.

“We met there Saturday morning, and we had some briefing from some key people from Inland Fisheries that have experience with this operation; personal protection equipment training and radio training and safety concerns,” Feltmate told The Journal.

Feltmate added, “We were pleasantly surprised that there was no interaction from the public; no one came just to see what was happening. We had made this real public and there was overwhelming support of all the communities and government entities, too, for that matter…It was a lot of work went into it; a lot of planning.”

How successful the application was in eradicating the smallmouth bass will be determined over time.

“Now the next few days is going to be monitoring the lake’s water conditions and, of course, the end results won’t be apparent for a few days as of yet. The Inland Fisheries people are presently monitoring the lake’s water conditions and the outflows so they are continuing with their work to complete the project. For the major part it, all went well but I do believe that was due to the extremely good planning on the part of the Inland Fisheries,” said Feltmate.

If the treatment of the lake is deemed a success, with no smallmouth bass remaining, trout which had been previously fished from Dobsons Lake and held in a pond near the site, will be reintroduced to the lake once the volunteers get the all-clear signal, said Feltmate.

“We’re thankful that we have hopefully eradicated these [smallmouth bass] out of this waterway and [that will] continue to protect this waterway for future generations and they can enjoy the same thing the people have now, the trout fishing and the splendour of these waterways in this area,” said Feltmate.

Rotenone is not a new strategy to combat invasive fish species in Nova Scotia lakes. In 2020, the treatment was used to eradicate smallmouth bass from Piper Lake in Pictou County. That lake now has some amphibians and fish returning as well as zooplankton, which is necessary to sustain fish populations.

The Dept. of Fisheries and Aquaculture noted in a Sept. 8 news release, “Public access is restricted at Dobsons Lake while Department staff and project team volunteers are onsite. Dobsons Lake will be monitored daily for several weeks after the rotenone treatment and periodically over the next several months. It will remain closed to recreational angling until it can support a sport fishery.”

Lois Ann Dort, Local Journalism Initiative Reporter, Guysborough Journal