The sea trout, lake trout and river trout are three different varieties of the same species. They all belong to the species Salmo trutta – the Latin name for the European trout. But what determines whether a small trout becomes one or the other? In fact, very little is known about this question. However, it is known that it is partly hereditary, partly determined by external circumstances.

Smoltification

If the little trout is to become a sea trout it must first – like the salmon – smoltify. This is a complicated process through which the little dark trout becomes silvery and slender of body. It will then be able to withstand saltwater. Typically the fish are 1-4 years old when they reach smolt size – in Denmark normally 2 years old. And then the smoltifying fish migrate downstream towards the sea in the spring, which happens in the darkest hours of the night. If they survive this first difficult period, they will grow quickly on a diet of bristle worms, crustaceans and small fry.

After a year or two in the sea, the sea trout becomes mature. It will then return to the stream where it was born in order to spawn, and will gradually assume its colourful spawning attire, which is most pronounced among the males. The skin becomes thicker and slimier as the otherwise very loose silvery scales become embedded in the skin. The males grow a very characteristic hook in their lower jaw and finally become brown all over. In contrast, the females keep their shape and only turn from silvery to brass-coloured while they are filling up with roe.

The dominance of the fair sex

As mentioned, females dominate the stock of sea trout. However, the males, which are in a minority, often become mature after spending only six months at sea. They then ascend to spawn – and are often of a size that is below the minimum fishing limit. The females usually stay an extra year in the sea before becoming mature. They are therefore considerably bigger than the males, and unlike the salmon, most trout survive spawning and are able to breed several times. The females have the highest survival rate.

When the fish become mature, they start moving back towards freshwater. During their search for freshwater they often come quite close to the shore – especially during the small hours of the night – and are thus very likely to end their lives in the gillnets some anglers set up quite illegally on the shore itself.. As the females spend longer at sea than the males, it is they who are most exposed to this netting. At the same time, the females are of greater importance to the population, which makes this netting close to the shore doubly unfortunate.

The time of ascent

The time of their ascent varies from one stream to another, but generally the biggest streams have the earliest ascent – in early summer or even late spring. In contrast, the smallest rivers and brooks do not experience their ascent until just before breeding. The decisive factor here is the amount of water, and before the autumn rains come there is simply not enough water in these small streams. In exactly the same way, dry summers may delay the ascent in the bigger streams. Equally, the small streams may experience an earlier ascent in rainy years.

In the springtime, you ought to turn your attention to the smaller, silvery and not yet mature ”Greenlander”, which often migrate into the lower reaches of the streams. This migration occurs primarily from areas with high salinity – and particularly during cold hard winters. What forces the Greenlanders into the freshwater of the rivers is the combination of low water temperature and the high salinity of the sea and fjords. Cold winters therefore usually mean a good ascent of Greenlanders in the rivers, and good fishing for these wonderful fish at the start of the season.

Favourite haunts of the Greenlanders

The Greenlanders typically stay in the quieter places in the river – in big “holes” where the backwater circles round and round and may be a little warmer than the surrounding water. In all events, they are to be found in places where they do not have to fight the current. Their metabolism is low in the cold water, and they save their energy. On the other hand – and unlike the spawners – they feed, and are therefore to be caught. Unfortunately many of them are females that are just below the minimum size limit and have to be put back.