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