A long search for the birthplace of Lake Wānaka salmon has raised hopes to help protect their struggling population.

Otago Fish & Game has been surveying Southern Lakes tributaries for spawning land-locked Chinook salmon for the past five years.

Surveys had found salmon spawning sites in the Hāwea and Wakatipu catchments, but the location of Wānaka sites remained a mystery until now.

"We’re relieved to finally locate one of the spawning locations for Lake Wānaka salmon," Cromwell-based Otago Fish & Game officer Mason Court said.

"While lake Hāwea and Wakatipu have productive salmon fisheries, the Wānaka salmon population has been struggling."

The spawning salmon were spotted this winter in an unnamed tributary of the Makarora River during an on-foot survey of possible historic spawning locations.

"We can now work with landowners and other agencies to assess how we can improve this stream’s conditions to support salmon spawning in the Wānaka catchment."

Fish & Game officers would continue the search for other Wānaka salmon spawning streams, Mr Court said.

Previously, Fish & Game had taken eDNA water samples from Makarora River to work out the upper limit of the salmon population. Although the samples had tested positive for the past two years, spawning salmon had not been visually sighted.

"Land-locked salmon are smaller than sea-run salmon, and therefore are harder to spot using a helicopter," Mr Court said.

"So, we’ve relied on old-fashioned foot surveys combined with high-tech eDNA testing to find them".

"Another challenge is that, like all Pacific salmon, Chinook salmon die after spawning, and their remains are quickly consumed by birds, mammals, trout and eels".

"They vanish from sight with barely a trace."

Chinook salmon were introduced to some South Island rivers from California in 1901 and began spawning, creating a valued sports fishery.

The salmon in the Southern Lakes have been landlocked since Roxburgh Dam was built in 1953 and are among of the purest strains of the species in the world.

The bright-silver fish range in size from only 500 grams to 1kg and are highly regarded for their eating qualities.

"The Wānaka salmon population declined in the early 2010s due to unknown reasons," Mr Court said.

Under a 10-year management sportsfish plan, Otago Fish & Game committed significant resources to the Upper Clutha salmon fishery.

In the 2020-21 season, Fish & Game surveys recorded only 17 salmon caught by anglers in Lake Wānaka, Mr Court said.

"The numbers are still low.

"The decline in the Wānaka population is suspected to have affected sea-run populations of the lower Clutha River/Mata-au."

A previous study found more than 60 per cent of sea-run salmon caught by anglers in the lower Clutha River/Mata-au were the progeny of land-locked lake-rearing populations above the Clyde and Roxburgh dams.

Anyone who sights salmon in the Wānaka catchment river system is asked to contact Otago Fish & Game.

© Scoop Media