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Trout and salmon

by  Carl Walrond

From the late 1800s, British settlers introduced fish of the Salmonidae family – trout and salmon – to New Zealand. Many species were released, yet only three established themselves well enough to form important fisheries: brown trout, rainbow trout and Chinook salmon.


Brown trout

Brown trout (Salmo trutta) form the basis of most freshwater fishing in New Zealand.

A successful import

From the late 1860s brown trout, from Europe, were introduced throughout New Zealand for fishing. They established themselves rapidly where they were released – and also spread by going out to sea and swimming up other rivers. In the early years they were very well conditioned. Some were so fat they looked like rugby balls, and could weigh over 10 kilograms.

After the initial boom, average trout sizes dropped. Acclimatisation societies had set up hatcheries and continued to release small fish into the rivers for decades. The rationale was that there was competition from predators such as eels and shags, but research has since shown this to be a waste of effort, as natural spawning provides more than enough young fish.

Habitat

Brown trout live mainly in rivers, but are also found in diverse habitats from estuaries to subalpine lakes.

Feeding

Brown trout are predatory fish that eat small aquatic insects and small fish. In flowing water they tend to face upstream, feeding on drifting aquatic insects. In slow-moving pools, brown trout cruise looking for food. In lakes they cruise the shallow zone close to shore, feeding on small fish such as bullies, and invertebrates such as dragonfly nymphs and snails in weed beds.

Brown trout often hide under rocks and streamside vegetation, and immediately seek cover if they see movement on the riverbank. As a result, they are one of the most difficult freshwater fish to catch.

Chasing rainbow – or brown

One angler weighed up the pros and cons of fishing for rainbow or brown trout: ‘The choice between the rainbow – often easier to hook and harder to land, and the brown – always harder to hook and sometimes easier to land, is a matter of taste and style, and there are no rights and wrongs in the matter.’ 1

Features

The body form and behaviour of brown trout are adapted for living in rivers. For example, their pectoral fins are much larger than those of rainbow trout. This allows them to use the river flow to hug the riverbed, where the current is slower and it takes less energy to stay in the feeding position.

In New Zealand brown trout often reach 800 millimetres and 5 kilograms. Most fish caught by anglers are smaller – typically 1–2 kilograms.

Distribution

Brown trout are found south of the Coromandel Peninsula. They prefer lower summer water temperatures than rainbow trout do, and winter water temperatures over 11°C kill brown trout eggs.

Life cycle

  • The female lays several hundred to several thousand eggs in a small hole. These are fertilised by the male.
  • After a month or two the eggs hatch, and the fry live in the gravel before emerging and feeding along stream margins.
  • Adults spawn in early winter, usually in the headwaters of streams with gravel beds.

Adults usually survive spawning and spawn annually. Brown trout live for 8–10 years, although individuals up to 15 years old have been recorded in New Zealand.

Sea-going trout

In the late 1800s and early 1900s it was thought that sea trout were a different species from riverine trout. But it has long been known that some brown trout live in estuaries and also go out to sea. Today it is accepted that riverine and sea trout are merely variants of brown trout.

Brown trout’s colours can change depending upon the waterway they live in. Sea-run trout can be a bright silvery colour, brown trout from rivers tend to be golden brown, and those from lakes are a duller silver. All have black spots, and riverine browns also have red spots.

Footnotes
  1. R. M. McDowall, The Reed field guide to New Zealand freshwater fishes. Auckland: Reed, 2000, p. 256. › Back

Rainbow trout

Rainbow trout (Oncorhynchus mykiss) were first introduced to New Zealand in the early 1880s. They are descended mainly from Californian steelheads – rainbow trout that migrate to sea and spend most of their lives there. However, New Zealand rainbow trout do not migrate to sea.

‘It was a whopper’

Anglers have long been notorious for their exaggerations. In 1888 a writer noted: ‘There are several kinds of trout liars. The liar of weights, who never catches more than half a dozen trout a day, but they can weigh anywhere from 8 lb to 10 lb. Then there is the liar of numbers, who always catches so many dozens in an hour and 28 minutes. And there is the liar of places, who knows hidden pools, dark and still, in the secret places of the rocks that are just boiling over with trout … and you fish in them for eight mortal hours without a nibble.’ 1

Distribution

Rainbow trout are less widespread than brown trout. There has been virtually no natural dispersal.

Ova imported in 1883 by the Auckland Acclimatisation Society survived, and fry were released into local waterways. In 1892 the species was liberated in Lake Rotorua, and in 1897 in Lake Taupō.

Rainbow trout can tolerate higher water temperatures than brown trout: they are found in warmer waters such as the Kai Iwi lakes in Northland. They also occur in a few rivers.

Rivers: limited success

Stocks were also released into many rivers, but they mostly disappeared. Nearly all the rivers where they did establish themselves flow into large lakes – in the central North Island, and the southern South Island.

It is not understood why rainbows have failed to become established in many waterways. Adding to the mystery is their presence in a few rivers that do not drain into lakes, such as the Pelorus and Rai in the South Island, and the Mōhaka in the North Island. These have very stable riverbeds, which may be a factor.

Taupō trout

Soon after they were brought to New Zealand, rainbow trout grew very large in Lake Taupō, but then declined in size. The average weight of trout in one angler’s bag was 10½ pounds (4.8 kilograms) in 1911, but by 1918 it had dwindled to 4 pounds (1.8 kilograms). The early bonanza was probably due to the trout feeding on the then plentiful native fish.

Feeding

Rainbow trout eat more and grow faster than brown trout. In rivers they feed in fast water, using energy to stay in the same place while feeding on drifting invertebrates. In lakes, rainbows tend to live in deeper water than brown trout and often feed on different prey – usually small fish, such as smelt in Lake Taupō.

This may explain why rainbow trout are bold feeders, more easily caught than the wary brown trout.

Features

Rainbow trout may reach 750 millimetres and more than 10 kilograms in New Zealand. Fish of 600 millimetres and 2–3 kilograms are often caught, and fish weighing 4–5 kg are not uncommon.

Most rainbows tend to live for four or five years, although individuals up to 11 years old have been recorded.

Life cycle

  • Several hundred to several thousand eggs are laid in a small hole by the female and fertilised by the male.
  • After 1–3 months the eggs hatch into alevins (fry with yolk sacs attached). These live in the gravel, feeding from their yolk sac.
  • They then emerge as fry, about 25 millimetres long. By late summer they have reached 50–70 millimetres.
  • As juveniles and spawning adults they live in streams, where they are exposed to predators on the banks.
  • Adults usually run upstream from a lake to spawn in late winter and early spring, in headwater streams with gravel beds. Not all rainbow trout survive spawning.

Much of the central North Island winter fishing is centred on rainbow trout running upstream from Lake Taupō to spawn in tributaries such as the famed Tongariro River.

Footnotes
  1. Jock Scott, Otago Witness, 23 March 1888, p. 28. › Back

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.

Features

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.

Distribution

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.

Life cycle

  • 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.

Variable runs

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.

Ocean ranching

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.

Commercial farms

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.

Footnotes
  1. Martin Unwin, quoted in Derek Grzelewski, ‘Salmon the miracle fish.’ New Zealand Geographic 63 (May–June 2003), pp. 39–40. › Back

Other salmonids

In the late 1800s and early 1900s attempts were made to introduce other salmonid species such as whitefish, Atlantic salmon, brook char and mackinaw – but with little success.

Whitefish (Coregonus clupeaformis)

Much effort went into acclimatising this species, native to high-latitude lakes in the northern hemisphere. From 1876 to 1907 nearly 10 million ova were brought in. Some whitefish were hatched and released into lakes, but the species never became established.

Atlantic salmon (Salmo salar)

The Atlantic salmon is native to rivers draining to the North Atlantic Ocean. Early settlers from Britain were familiar with the fish and eager to establish sea-going salmon populations. Between 1864 and 1910, 24 introductions were attempted involving 5 million ova, but with very little success.

There were local fisheries at Lake Te Anau and Lake Manapōuri and in the Waiau River in the 1920s and 1930s, but the fish were poorly conditioned and did not swim out to sea. They weighed only about 2 kilograms, whereas Atlantic salmon in Britain returning from the sea were typically four times that weight.

The species is considered to be close to extinction in New Zealand, with remnant wild stocks confined to lakes in Southland’s upper Waiau catchment.

Brook char (Salvelinus fontinalis)

Brook char were first introduced in the late 1870s or early 1880s. They were widely released, but it seems they could not compete with brown trout. They still exist in headwaters of some catchments, such as the upper reaches of the Shag River in Otago, but they are usually very small (typically only 150 millimetres).

Lake Emily, inland from Ashburton, is the best fishery, where brook char up to 600 millimetres and 3 kilograms may be caught.

Lake char or mackinaw (Salvelinus namaycush)

The mackinaw is native to northern North American lakes, where it can grow up to 46 kilograms. The only New Zealand population occurs in Lake Pearson, in the headwaters of the Waimakariri River.

The species arrived in 1906 and was destined for Lake Kaniere on the West Coast. But as they were being transported towards Arthur’s Pass, the temperature of the water containing the fish rose too high. Fearing that the mackinaw would die, the acclimatisers dumped them in nearby Lake Pearson and Lake Grassmere. A population still exists in Lake Pearson, but the typical weight of less than 1 kilogram suggests that it is not an ideal habitat. In New Zealand mackinaw are little more than a curiosity.

Sockeye salmon (Oncorhynchus nerka)

Sockeye were released into the Waitaki River catchment in 1902, after some 500,000 ova were gifted by the Canadian government.

Young that hatched were released in the hope of yielding a returning run, to develop a commercial fishery based on canning salmon. The species established itself in Lake Ōhau but a sea-going population never developed. A remnant population still exists in Lake Ōhau and its tributaries.


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How to cite this page: Carl Walrond, 'Trout and salmon', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/trout-and-salmon/print (accessed 11 December 2019)

He kōrero nā Carl Walrond, i tāngia i te 24 Nov 2008