Chapter 1 – Where Do Sea-Run Trout Come From?
The Complete Guide to Sea-Run Trout Fishing by Allan Burgess
In the late 1800s, it was widely believed that silver-coloured sea-run brown trout; and darker coloured resident river brown trout, were two different species. It is now accepted that they are the same species. Although many knowledgeable people on the subject are convinced that they are different strains of the same brown trout species.
Interestingly little research has been undertaken into the mysteries of sea-run brown trout in New Zealand. Although much can be pieced together, and other things assumed, there are still many questions left unanswered.
For example; how many brown trout enter certain rivers? What percentage of brown trout are sea migratory? Where do they go while at sea? There are many things we don’t know about them.
Originally our brown trout originated from Europe. They were introduced into New Zealand from stocks that had already been established in Tasmania, Australia. The first unsuccessful shipment of brown trout ova was sent to Tasmania from Europe as early as 1848. However, they were not successful until 1864.
The problem was transporting ova by sailing ship from Great Britain such a long-distance across the heat of the tropics. Back then the journey took many weeks. The New Zealanders thought it prudent to wait and see how the Australians fared rather than attempting to import their own brown trout ova from Great Britain themselves. The Southland and Canterbury Provincial Councils made very significant financial contributions to the Australian cause.
Importations into New Zealand began as early as 1867. Numerous further importations took place over the following 20 years. When attempting to import trout from one country to another it is more likely to result in success if ova are transported instead of live fry. Ice can be used to keep the ova cool which slows their development without any detrimental effects on the numbers that hatch.
Numerous different importations took place with ova from different places resulting in a mixture of genes including both resident river fish and known sea-migratory populations. The best sea-run trout fisheries in New Zealand are located in the rivers of the South Island’s east coast, particularly Canterbury. There are also good numbers of sea-run browns in Otago and Southland’s coastal rivers.
The main reason for the excellent sea-run brown trout fishing in Canterbury may lie in the nature of the rivers themselves. The Hurunui, Waimakariri, Rakaia, Rangitata and Waitaki Rivers are all subject to flooding, discolouration, low-flows, and constantly changing channels that generally provide poor habitat and forage for trout. We know that as juvenile trout grow from fry in their small hatchery streams they steadily migrate to larger water where there are more prey and shelter. Perhaps eventually going to sea is a natural continuation of this process.
Perhaps the sea-running browns in Canterbury are sea migratory as a counter to these constantly changing river conditions. In the spring and summer when there are enormous numbers of whitebait and smelt, together with terrestrial insects, the sea-runs return to take advantage of this bounty. We can think of them living in both the river and sea migrating back and forth in order to best take advantage of suitable prey species.
This type of migratory behaviour is not in the least unusual among fishes. Vast schools of kahawai and barracouta arrive off the coast to take advantage of the seasonal abundance of sprats and pilchards over the summer months. Then they move north or out to deeper water over the winter months.
Research overseas with sea-run rainbow trout (steelhead) has shown that some of the ova hatch and the fish later become silver before heading out to sea. When they return and enter the rivers to spawn in the stream of their birth they assume the typical river fish colouration. After spawning, they become silver again and can repeat this spawning cycle several times throughout their lives.
Sea-run rainbows spend at least one winter at sea. I think we can assume that this pattern is similar for sea-run brown trout in New Zealand. So in answer to the question of where do sea-run trout come from; probably they remain at sea for part of their lives, particularly during the winter months, returning to the lower rivers when their food supply of whitebait and smelt returns, and when they are ready to spawn.
Sea-run trout are bright silver in 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, particularly the smaller ones, also have red spots. Brown trout living in the tannin-stained streams and lakes on the West Coast of New Zealand’s South Island are often a buttery yellow with a slight greenish tint to their skin colour.
The skin colouration of brown trout can change depending upon where they live. Presumably, they change colour to better match their surroundings, making it more difficult for their prey to see them, and also to make it harder for predators to catch them in turn. The change to the darker river colouring may also help to attract a mate.
Brown trout don’t usually have spots on their tails which makes it easier to distinguish them from rainbow trout. To me, brown trout look quite different from salmon even though sometimes the colour can be very similar.
In Lake Coleridge, up in the Canterbury high country, the rainbow trout and the landlocked Quinnat salmon can be difficult to tell apart with both species tending to become quite silver in colour. There is a limited food supply in Lake Coleridge and most of the fish are in relatively poor condition
for their length.
Bright silver sea-run brown trout returning to the rivers from the sea eventually become darker as they head upriver to spawn. But unlike salmon that die soon after spawning sea-run brown trout can repeat the process several times over their life-span. Brown trout spawn in autumn and early winter. Both salmon and trout only spawn in freshwater. So even if they are in fact moving in and out of the rivers more regularly in search of food supplies we know that they have to return to the rivers to breed.
Rainbow trout (Oncorhynchus mykiss) were first introduced to New Zealand in the early 1880s. They are descended mainly from Californian steelheads. These are rainbow trout that migrate to sea and spend most of their lives there. However, New Zealand rainbow trout do not migrate to sea even though some of the rainbow trout ova imported into New Zealand came from sea-run fish or steelhead stock.
NIWA report that one brown trout specimen that was tagged near Christchurch was later recaptured in the Mataura River (a distance of several hundred miles), while another tagged in the Wanganui River system turned up in Taranaki 125 days later.
In another article by Gavin James of NIWA, it was found that trawler-caught salmon taken in the Canterbury Bight fed mainly on fish, with sprats making up 76 percent and juvenile hoki 5 percent of their diet. Salmon also ate the reddish swarming krill known as Munida. As far as I am aware there has been no research published on what sea-run trout eat at sea. I would assume that their diet while in the ocean would be similar to that of the salmon but it may not be. They are almost certainly going to be eating whatever is seasonally abundant at the time. While carrying out research for this book I was surprised at just how little information there is available about sea-run brown trout in New Zealand. Most of what is known is passed down from successful anglers rather than resulting from extensive scientific study.
Sea-run brown trout usually have flesh that is more orange, firmer and better eating than resident river brown trout. Many anglers complain that river-dwelling browns taste like mud!
Sea-run brown trout enter the river mouths in pursuit of whitebait and smelt. They are therefore timing their run to coincide with the arrival of these prey species. I have caught sea-run brown trout that have disgorged huge numbers of silveries as I have lifted them from the water. Their stomachs being jammed packed with smelt. Sea-run trout can disappear from the lower rivers almost overnight should this rich food supply suddenly dry up.
Over the years I have fished the Rakaia River mouth in the company of other anglers night after night. Each night many fish are caught. Then suddenly one evening no one will be catching any sea-runs at all. They may all but disappear for nights on end. Then perhaps a week later they are back. They do seem to come and go at times. Perhaps the whitebait and silveries have become scarce so they have decided to move elsewhere!
Keep in mind also that salmonids are very flexible with regard to life in both fresh and saltwater. Sea-run brown trout will move in and out of the surf zone as river conditions and the food supply dictates. I have on many occasions been fishing at the mouth of the Rakaia River and witnessed as many trout being caught on the seaward side of the shingle spit as I have in the river itself. It can seem strange to be trout fishing in the sea but sometimes that is where the fish are feeding.
The numbers of smelt and whitebait returning to the rivers at times is just phenomenal. I have dipped my whitebait net into the water and caught dozens of smelt (also known in Canterbury as silveries) in just a few seconds.
The numbers of smelt entering the rivers must run into many millions. I have seen a smelt jump out of the water with a trout in pursuit only for the same smelt to be taken by a diving tern.
Brown trout, like all salmonids, grow very quickly when there is a good food supply. So the huge bonanza of whitebait and smelt starting in the spring cause the sea-run brown trout to grow quickly and put on condition.
You can see from the pictures in this book that some of the sea-run trout appear quite thin while others are deep-bodied solid looking fish.
Interestingly whitebait and smelt lay their eggs in margins of freshwater, rivers, creeks and lagoons. After hatching the small larval fish are washed out to sea where they spend the winter. The juveniles then return from the sea in the spring. So smelt and whitebait are also sea-migratory.
Many readers may be unaware that large sea-run brown trout are sometimes caught from ocean beaches miles from any river-mouth. In my experience, these are usually bigger fish in top condition. I have done a great deal of surfcasting over the years. One thing I like to do after putting out a baited hook rig when surfcasting is to spin fish with a ticer on a long rod and try to pick up a kahawai or two. Even when there are no birds working it is surprising how often this is successful. On occasion, I have hooked and landed a big sea-run brown trout as an unexpected bonus. I have landed sea-run browns at Birdlings Flat, Conway Flat, Kaikoura and Marlborough while spinning for kahawai.
It always amazes me that big trout can spot and catch small whitebait and smelt in fast-flowing water that is often discoloured from snowmelt. Furthermore, the sea-run browns are quite happily able to continue successfully hunting even when it gets dark.
Later in the season, after Christmas, as the rivers clear, and salmon anglers fish the river mouths by day, the trout become harder to catch and are more productively targeted at night. During the long summer evenings, after hot days when there are still plenty of smelt running, night fishing for sea-run trout is very pleasurable and more productive than during the day.