Mystery of Wānaka's 'missing' salmon takes another step towards being solved

A hidden spawning stream high in the Upper Clutha catchment has revealed another secret.

Otago Fish & Game, working in partnership with the Clutha Mata-Au Sportsfish and Habitat Trust, has discovered only the second known spawning site for Lake Wānaka's elusive landlocked Chinook salmon, after years of detective work to find out where the fish reproduce.

For decades, anglers have known the salmon are still in Lake Wānaka, but no one knew exactly where they were spawning after the population declined steeply in the early 2000s.

Pictured: A rare find … Otago Fish & Game officer Cole Briggs holds two spent Chinook salmon recovered from a remote Upper Clutha stream during this winter's search for the fish's elusive spawning grounds. Photo: Mason Court, Otago Fish & Game.

Catch rates for salmon in Lake Wānaka crashed despite anglers still reeling in good numbers of the species in neighbouring lakes Wakatipu and Hāwea.

The first breakthrough came in 2023, when spawning salmon were found in a small tributary of the Makarora River. This winter, Fish & Game staff struck silver again, locating a second spawning site in the Wilkin River catchment.

The discovery gives researchers another crucial location to monitor, helping answer long-standing questions about the future of this salmon fishery.

"It's a major step forward," Otago Fish & Game officer Mason Court said.

"For many years we knew these fish were still there, but we had very little understanding of where they were spawning."

The search is far from straightforward. Unlike large salmon that return from the sea, Wānaka's landlocked Chinook are smaller and difficult to survey with aerial monitoring. They spawn in remote streams and die soon afterwards, leaving only a brief window each winter for researchers to find them.

The latest discovery was also helped by anglers who reported salmon catches and sightings around the Upper Clutha, giving researchers valuable clues about where to look next.

"We'd like to sincerely thank the anglers who have taken the time to report their catches and sightings," Mr Court said. "Their information has directly contributed to improving our understanding of this fishery."

Fish & Game staff collected tissue samples for DNA analysis and removed otoliths (ear bones) from spent (post-spawning) salmon. These samples will contribute to ongoing research to better understand the genetics, life history, and movement of the Lake Wānaka Chinook salmon population.

To complement the spawning surveys, environmental DNA (eDNA) samples have also been gathered from the upper catchment. The results expected in the coming weeks will help determine whether other spawning locations exist within the Lake Wānaka catchment.

Previous research using otolith microchemistry found that, in some years, Lake Wānaka fish made up the majority of Chinook salmon captured downstream of Roxburgh Dam, highlighting the importance of understanding and protecting their remaining spawning habitat.