The effort to save one of Canada’s most endangered freshwater fish now involves electronic tracking of specimens bred in captivity and released into the Nova Scotia watershed that holds the world’s only remaining wild population.
Last week, a final batch of 30 tagged Atlantic whitefish were released in the Petite Rivière system behind the town of Bridgewater on the province’s South Shore.
“We have released fish into different parts of the system, the lake portion, riverine portion and as well into the estuary into salt water,” said Jeremy Broome, a biologist with Fisheries and Oceans Canada assigned to the recovery team.
“So looking at which one of those might produce the best survival is important to us.”
Tags inserted with needle
Tiny transponder tags were inserted with a hypodermic needle into 150 one-year-old fish spawned at the Dalhousie University Aquatron marine research facility in Halifax.
The fish were anesthetized, given one week to recover and released at various locations within the watershed. Fish were released into the estuary after acclimatizing to saltwater.
Devices installed at narrow points along the river system will send a signal when a tagged fish swims by.
“We are trialling different approaches, sort of spreading our eggs across different baskets to see what might work best,” Broome said.
“If we can determine that survival is better with releases into the estuary, we’re seeing more fish come back from that strategy that would be indicative that we would want to proceed with that approach.”
Landlocked for a century
This whitefish species is an ancient relative of Atlantic salmon and naturally anadromous, meaning they’re born in freshwater, travel to the ocean and return to spawn.
They have survived only in the Petite Rivière watershed, which was landlocked for a century by a dam and serves as the water supply for the Town of Bridgewater.
A fish ladder was built there in 2012.
The recovery team hopes to see evidence that 1,100 untagged juveniles released last year and those tagged in 2023 return to spawn in the next year or two.
Why the Atlantic whitefish is in trouble
Nearly 40 years ago, the species was the first fish in Canada to be assessed as endangered by the Committee on the Status of Endangered Wildlife.
The whitefish faces several threats including warming waters and invasive smallmouth bass and chain pickerel introduced into the watershed.
Atlantic whitefish are now so scarce that when found, the young are whisked an hour away to the Aquatron, where a captive breeding program is underway.
Unlike previous years, no juvenile or larval whitefish were captured in traps installed throughout the system this spring.
Dalhousie’s Aquatron now holds more Atlantic whitefish than exist in the wild.
“Without the brood stock that we’ve been able to develop at that facility and the progeny that are coming from there now, we really would be out of options. We’re still not in a great place, but without that facility and without that program we’d be in a very dire place,” said Broome.
Looking for another home
The recovery team is also looking for other watersheds in Nova Scotia where the critically endangered species could be introduced and survive.
Several candidate sites have been identified and surveys are planned this summer. Consultations are the next step.
“I think we’re at a point where we have to make a move and we have to start trying these things,” he said.
A 20-year recovery merry-go-round
After it was first declared a species at risk in 2003, a captive breeding program was established at the Mersey Biodiversity Centre in Nova Scotia as part of a government-mandated recovery strategy.
The program was shut down and the Mersey diversity centre literally bulldozed under the Harper government in 2013.
Several months later, the voracious invasive chain pickerel were discovered in the Petite Rivière watershed, which held the remaining wild population.
Thousands of whitefish reared in the diversity centre had been released into a holding lake behind the Burnside industrial park in Dartmouth. None survived.
No adult whitefish were seen alive between 2014, when the chain pickerel became established, and 2018.
Dalhousie to the rescue
Since then, Dalhousie intervened to offer its Aquatron facility, first as a Noah’s Ark to save the species from risk of extinction and later to host a captive breeding program.
The university has also been involved in building a streamside rearing facility — a miniature component of the diversity centre that was demolished by the previous federal government.
Even the reintroduction into the Petite Rivière system is a repeat of the work of the cancelled captive breeding program.
Still, Broome remains hopeful.
“This is truly, this is a Nova Scotia species of fish. It’s only found here, only in the province, the only place in the entire world,” he said.
“So it’s ours to do something about. It’s ours to protect and keep on the face of the planet.”
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