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 and while surveys had found salmon spawning sites in nearby catchments, the Wānaka sites remained a mystery until now.

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

“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.

Otago Fish & Game officer Ben Sowry with a land-locked salmon caught in Lake Hāwea. PHOTO: Bruce Quirey, Otago Fish & Game

“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 will continue the search for other Wānaka salmon spawning streams, Mason said.

The organisation had previously taken eDNA water samples from Makarora River to work out the upper limit of the salmon population but even though 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,” Mason 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 the purest strains of the species in the world.

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

“The Wānaka salmon population declined in the early 2010s due to unknown reasons,” Mason 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, Mason said, but 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 percent 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.