Story: Trout and salmon
Page 3 – Chinook salmon
Chinook or quinnat salmon (Oncorhynchus tshawytscha) are native to the north-west coast of North America, and north-east Asia.
Release in New Zealand
New Zealand remains the only place in the world where Chinook salmon have become established successfully outside their natural range.
In the early 1900s they were introduced from ova sourced from the McCloud River in California. They were released into the Hakataramea River, a tributary of the Waitaki River in the South Island. They were soon running up other Canterbury rivers such as the Rakaia and Rangitātā.
Chinook are the largest species of the Salmonidae family in New Zealand, commonly reaching 10–15 kilograms. Most adults are three years old when they spawn. When they enter river mouths on their spawning runs, they are very silvery in colour – but this gets duller the longer they stay in fresh water.
Salmon are found mainly on the South Island’s east coast, from the Waiau River in North Canterbury to the Clutha River in South Otago. There are also small runs in the Paringa, Taramakau and Hokitika rivers on the West Coast
The renowned fisheries are the Waitaki, Rangitātā, Rakaia and Waimakariri rivers. Once, smaller rivers such as the Ashburton and Ōpihi also supported salmon.
Taking water for irrigation has seen these rivers suffer from river mouth closure in summer. In the 2000s they were no longer regarded as good salmon fisheries.
Small landlocked Chinook salmon can also be caught in some South Island lakes such as Lake Wakatipu. Dams on the Clutha River prevent them migrating to sea, so they never grow to any great size (they are typically less than 1 kilogram).
Occasionally stray salmon are found in North Island rivers.
- Females and males pair up and the female digs a depression in a gravel stream bed and lays eggs. The male deposits his milt to fertilise them.
- Eggs hatch into alevins (fry with yolk sacs attached) in spring. After the yolk sac is used up, the fry emerge from river gravels in streams that they use for spawning. They spend about three months swimming downstream, entering the ocean in summer.
- In the sea the young salmon feed on small fish and crustaceans, and grow rapidly into adults.
- At maturity (3–4 years) they swim upstream in ‘runs’ or large numbers to spawn in the upper reaches of rivers.
- After spawning all adults die.
The size of salmon runs changes from year to year. The best river was the Waitaki, but much of its glory was lost after the government built a dam at Kurow in 1935 – greatly reducing the size of the salmon run from perhaps 100,000 fish to 10,000. A fish ladder was built up the side of the dam but it was poorly designed and never worked.
In the 2000s, upriver runs consist of a few thousand fish in each of the main rivers. Anglers probably catch 35–40% of them. In any given year the total run has varied between 10,000 and 75,000 fish – most years being at the lower end.
Hatcheries: attempts to raise numbers
The variability of salmon runs led to efforts to enhance the size by hatching and releasing young salmon. In Canterbury, wild salmon were trapped and stripped of ova in spawning streams.
During the 1980s, fish reared in hatcheries on the Rakaia River increased the size of runs. But the cost per fish reared was too high, and runs were still variable.
There were also plans for ‘ocean ranching’ – commercialising the fishery – in the 1970s and 1980s. The theory was that hundreds of thousands of salmon would be hatched from ova and released. They would go to sea and feed at no cost and come back as adults to be harvested. The plans went ahead and the salmon were released, but they did not come back.
In the 2000s commercial salmon farms operated at South Island freshwater sites such as Waikoropupū Springs near Tākaka, and the Tekapo canal in the Mackenzie country. But most farmed salmon were reared in sea cages in the Marlborough Sounds and Stewart Island.
The price of fish
‘The average survival rate for smolt [young salmon migrating to the sea] is less than one per cent, and anglers catch about a third of the returning fish, so for every salmon caught you have to release 300 smolt. To significantly improve the number of returning salmon you’d have to annually release 300,000 to 500,000 smolt, and they cost a dollar each to rear. This means each fish costs between $300 and $500.’ 1
Why do runs vary?
Research suggests that conditions out at sea may determine the number of salmon that return.
Conditions in the rivers are also a factor. In spring and summer, juvenile salmon make their way downriver to the sea. Floods can kill juveniles or wash them out to sea. Stable flows give them a chance to stay longer in the river and so reach a greater size by the time they go to sea. Those that get to sea at three months of age make up 75% of returning adults.