New Brunswick

Native fish could die alongside invasive ones under eradication plan

Department of Fisheries and Oceans scientists say there's no point trying to save some of the native fish in a New Brunswick lake that may soon be deliberately poisoned to eradicate smallmouth bass.

DFO scientists believe native fish will repopulate Miramichi Lake naturally over time

Invasive smallmouth bass are viewed as a serious threat to salmon if allowed to become established in the Miramichi River system (U.S. Fish and Wildlife Service)

Department of Fisheries and Oceans scientists say there's no point trying to save some of the native fish in a New Brunswick lake that may soon be deliberately poisoned.

The report suggests fish in Miramichi Lake should be allowed to repopulate naturally in the years after it is treated with rotenone, a natural product that quickly kills fish and then dissipates on its own into the environment.

The DFO science review is in response to plans by salmon conservation groups hoping to eradicate invasive smallmouth bass from the 300 hectare lake.

If accepted it would mean all fish in the lake, invasive or native, would be killed by the treatment.

Smallmouth not native to region

The original plan for the lake was to remove some of the native fish, like white suckers and yellow perch, set them aside in tanks, then return them to the lake after the chemical had dissipated.

Smallmouth are not native anywhere in Atlantic Canada and are viewed as a serious threat to young Atlantic salmon if they are allowed to become established in the Miramichi River system. Smallmouth populations can grow quickly and turn to young salmon as a food source.

With the discovery last summer of smallmouth in the Southwest Miramichi downstream from the lake, the groups are now hoping to also treat about ten kilometres of the river itself at the same time, and at the same cost to native and non native fish alike. 

The North Shore Micmac District Council and the Miramichi Salmon Association and the Atlantic Salmon Federation are involved in the project.

The science review is dated Oct. 21 but was released publicly last week.

It acknowledges "an ongoing risk of spread and establishment" of smallmouth bass in the Miramichi River system, and that application of a "chemical piscicide" like rotenone is the most effective approach.

Mark Hambrook of the Miramichi Salmon Association said, 'I actually thought it was a pretty good review.' (Bridget Yard, CBC)

But the report questions the need to try to save some of the native fish that are now there for the purpose of recolonizing the lake.

"If the objective is to re-establish a naturalized lake ecosystem post-treatment, a reasonable option is to allow the recolonization to occur naturally," states the report, which lists 14 science branch employees as contributors.

It suggests the recovery of native fish populations in the lake could be studied to provide information for future cases where invasive fish must be eradicated.

Still some unknowns

"Most fish species in Miramichi Lake will likely be re-established through immigration from Lake Brook [from the Miramichi River] and the inlet streams."

It is not clear how long it will take for fish to recolonize the lake. The report says it is difficult to assess the impact rotenone will have on plankton and invertebrates in the lake.

"Much of the invertebrate food supply for fish, a vital component of fish habitat, will be temporarily (months to years) eliminated," it says.

While the document raises some concerns about the salmon groups' plan, the organizations involved welcome the document's recommendations.

Rotenone being applied to tiny Despres Lake in New Brunswick in 2001. Almost 700 invasive chain pickerel died along with 3,200 native yellow perch. (New Brunswick Department of Natural Resources)

"I actually thought it was a pretty good review," said Mark Hambrook, president of the Miramichi Salmon Association.

"I thought it just validated the whole application myself. I didn't see anything in there that would be, that points to something that says no, you should not do this."

Hambrook said the original plan to capture and hold thousands of native fish in tanks would be difficult and costly.

The Atlantic Salmon Federation is also happy with the report's findings.

"We're reassured by their conclusion that there is no good outcome for the native fish community if smallmouth bass remain in the lake or establish themselves in the river," said spokesperson Neville Crabbe.

Costs not known

Crabbe said eradication of invasive species is the responsibility of Fisheries and Oceans Canada.
He expects the federal department will pick up the cost for the project, which has not been determined.

The rotenone plan is not welcomed by many of the 13 camp owners along the shore of Miramichi Lake.

"The concern we have is the poison," said Sam Bell, who has summered on the lake for 60 years.

He fears there are long-term effects of rotenone that may not yet be known, and  he suspects the lake will not soon recolonize on its own after the fish are killed.

"That takes a lot of, lot of years," said Bell. "That lake is so pristine all those fish thrive in it."

Despite the release of the report, the application to use the rotenone must be approved by DFO managers in the Gulf of St. Lawrence region.


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