Steelhead in New Zealand – To Sea or Not to Sea? Often the Question

Steelhead in New Zealand – To Sea or Not to Sea? The Story of Sea-Run Acclimatised Sports Fish in New Zealand

by Malcolm Flain

This article has been reproduced from Freshwater Catch Autumn 1988 No 35. Freshwater Catch was published quarterly by MAFFish, New Zealand.

The introduction of salmonids to New Zealand waters in the late 1800s and early 1900s was done with scant knowledge of their native North American and European oceanic requirements and even less for ocean conditions around the New Zealand coast. Are there steelhead rainbows in New Zealand?

The results of these introductions, coupled with today’s knowledge of offshore sea conditions, clearly indicates why some species succeeded and others failed to establish in New Zealand. It also provides answers to those who still seek, in some instances, to develop sea-run stocks of certain species.

North American Salmonids

Chinook Salmon

The most obvious transplant success has been the introduction of chinook (quinnat) salmon from the west coast of North America. It has established significant sea-run stocks in most of the east coast, South Island, rivers. It is now known from major tagging programmes that this species in North America makes extensive near-shore migrations, and does not typically venture far offshore. These movements are also closely related to an upper-temperature isotherm of 15°C. Above this temperature at sea, this species is scarce.

Oceanic conditions off the South Island are very different from those of western North America. Fortunately, however, there is the cool Southland current at no great distance off the coast which contains local inshore waters normally of 15°C or less. It is within these waters that almost all chinook salmon have been taken at sea. A small number of chinook have been taken in warmer northern waters over the years, but these are clearly strays.

The conclusions I arrive at are as follows. The limited offshore migration pattern of the species, coupled with their upper limit of 15°C, meant that chinook transplants could succeed, and did so in east coast South Island rivers. It also explains why they have not succeeded in the North Island rivers. Similar reasoning was behind recommendations for the introduction of chinook to South America where of all species tried, it has been the most successful sea-run fish.

Totally freshwater resident (= “residual”) NZ sockeye salmon from Larch Stream, Lake Ohau. The top two are females, the bottom one is a male. Photo. R Goode.

Sockeye Salmon

Another species of Pacific salmon introduced to New Zealand was the sockeye salmon. This species is known to undertake extensive offshore migrations, but unlike North American chinook some progeny of a population remain, grow, and mature in freshwater lakes. These “residuals” are the reason why we still have sockeye in New Zealand today.

Sockeye ova were obtained from sea-run stocks from Shuswap Lake on the Fraser River. Fish were established in the Waitaki system by liberations into Lake Ohau. Though actively sought by researchers and anglers, no evidence of sea-run habit has ever been demonstrated.

However, freshwater spawning “residuals” were observed soon after the introduction of the species. In recent times the numbers of spawners have, on occasions, been counted in the thousands. Juveniles from these fish originally had free access to the sea, and substantial numbers almost certainly migrated to the sea.

Though there are now dams on the river, the juvenile out-migration to the sea is almost certainly still occurring to some degree. Despite this, there is no evidence that sea-run sockeye return to spawn.

The idea of developing a sea-run stock of sockeye has been frequently promoted. I would reason that because of the failure of the longstanding natural experiment in the Waitaki, any such proposals are almost certain to fail. Similarly, the introduction of pink salmon and chum salmon would also fail because of their known habit of extensive offshore migrations in North America.

The same may be true for most coho stocks. None of these Pacific salmon has “residual” freshwater populations except where egress from freshwater is completely denied.

Rainbow trout – Steelhead?

Rainbow trout in North America either complete their life cycle totally in freshwater or go to sea and return to freshwater only to spawn. The latter are known as “steelhead” or “steelhead rainbows”. This sea-run fish is also known to range large distances offshore.

Ova for New Zealand came from rainbow/steelhead runs from Sonoma Creek, a tributary to San Francisco Bay. Like the sockeye, freshwater stocks have firmly established, but there is no evidence for sea-run “steelhead” rainbows, despite reports to the contrary.

Scales taken from any so-called “sea-run” rainbow trout will clearly resolve such claims, although none so far have been forthcoming. No doubt some rainbows do go to sea, but because they go too far they get lost, like other far-ranging salmonids.

Brook Char

The brook char is another North American salmonid and was originally introduced into New Zealand from New York State. It also has freshwater populations and is known to go to sea, in this case seldom any great distance but sufiicient to invade new catchments.

Its widespread distribution in the headwaters of New Zealand rivers exceeds its early liberations. Therefore it seems that it has dispersed more widely via the sea, and in keeping with its North American habit, limited sea migration would achieve such dispersion. To date, no evidence of any sea residence in New Zealand brook char has been found.

European Salmonids

Two European salmonid species introduced into New Zealand repeat the same pattern shown by the North American introductions. Atlantic salmon from various European rivers go all the way to Greenland, but in some catchments, there are “residual” freshwater stocks.

Ova for New Zealand came from sea-run stocks. Introduction resulted in the establishment of “residual” freshwater stocks in Lake Te Anau, but no sea-run fish, even though access from the lake to the sea was available.

Because of its normal extensive offshore migration, the migrants almost certainly got lost in the completely different ocean and current regimes of the South Pacific.

Brown trout

European brown trout are mainly freshwater residents but, like the eastern North American brook char, do undertake limited migrations into the sea, and can invade new catchments by this means.

The brown trout stocks introduced into New Zealand show the same pattern. Most are caught in freshwater, but a small number are caught at sea, usually in gill nets close inshore.

It is claimed by some that there are runs of New Zealand “sea trout”. By inference, these are discreet self-perpetuating stocks possessing the sea-going characteristic. For this to be true such runs require a mechanism of separation to maintain their discreetness.

This could be by way of behavioural mating differences, temporal or spatial spawning separation, etc. However, evidence from scales does not support this belief.

A more plausible explanation is that a proportion of brown trout populations can and do go to sea, but these return at spawning time and interbreed with resident freshwater stocks.

They are not discreet. Southland rivers like the Pomahaka and Mataura are reported to have “sea-run” stocks of brown trout. It may be that local conditions encourage a higher proportion of fish to go to sea, and so these fish may be more apparent in spawning runs than are seen in other rivers.

Scales which show sea growth and one or more spawning checks with a return to the sea are very rare. This would not be the case if we were sampling a discreet spawning run of sea trout. I have repeatedly asked proponents of this concept to provide scale samples from discreet stocks of “sea-run” trout. To date, none have been forthcoming.

To sum up, we were lucky with the choice of chinook salmon. There never will be a run of wild sea-run sockeye salmon, Atlantic salmon, pink salmon, or chum salmon if they are ever introduced. “Steelhead” rainbow trout runs do not exist and are never likely to in New Zealand. Brook char are an unknown quantity, but it would not be a surprise for some to be taken close inshore.

Malcolm Flain was a scientist at MAFFish Christchurch.

This post was last modified on 28/05/2022 2:12 am

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