A single sea-run salmon per day is all Otago anglers will be allowed to take home after the bag limit was slashed amid claims the fishery is in crisis.

The Otago Fish and Game Council lowered the bag limit from two to one for the upcoming 2019-20 season, following a call from the National Sea Run Salmon Committee to South Island fish and game councils.

The committee described the salmon fishery as in crisis and said without immediate action it would continue to be severely depleted.

Otago Fish and Game officer Nigel Pacey said the numbers of fish harvested recently in the Clutha and Taieri rivers were almost non-existent.

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''We may reach a point where the wild fishery cannot recover. This will be totally devastating for anglers who value the fishery so highly.

''Anglers will need to be mindful of new regulations as they are introduced so that the worst-case scenario doesn't eventuate.''

The decline came from varied factors, Pacey said, believed to result mostly from effects at sea.

These included salmon caught as by-catch by trawlers, and rising sea temperatures due to climate change altering food patterns.

Water extraction for irrigation could also be behind the decline, along with the repeated loss of hundreds of salmon at the Dunedin Community Salmon hatchery in Sawyers Bay, which the trust chairman blamed on ''vandalism''.

Pacey noted the Otago Harbour's salmon fishery was not under the control of the fish and game council.

The new one-salmon limit comes into force on October 1.