The sea trout moved in as the ice receded and formed the River Karup valley. In other words, the sea trout’s history goes back more than 10,000 years in time.
That the sea trout still thrive there is not a given thing. Like most rivers in Denmark, and in the rest of the world, the River Karup and its many smaller tributaries have survived against all odds, and throughout most of the 20th century, the river’s stock of sea trout went from poor to terrible. As early as 1918, a hydro power plant was established in the village of Karup. This effectively barred the way for migrating sea trout to reach the spawning beds in the upper reaches of the river system.
In the 1930s, pollution from a potato starch factory destroyed a large part of the spawning grounds, from the village of Karup and 20 kilometers downstream. This and other polluting factories, like an industrial slaughterhouse and an intestinal cleaning factory, were built with complete disregard to wildlife. Though the local anglers struggled to change the tide, it took more than an angler’s patience until things finally changed: The potato starch pollution in the river, for instance, had devastating effects for all life in the river and it continued for nearly 45 years! Stocking of sea trout fry from other rivers were tried as a means to rebuild and strengthen the fish stocks. Later it became clear that this was only a short-term solution. Biologists proved that local strains by far outperform hatchery strains of trout. As a matter of fact, the success of wild trout in surviving and reproducing in the wild is much superior. As a consequence, stocking of young fish changed completely to fry from incubated eggs derived from mature wild sea trout caught within the River system by electro-fishing in the autumn. Today, the population of sea trout in the River Karup is self-sustaining and the stocking of fry has stopped. Over the years, many, many volunteers from the local angler’s associations have worked for countless hours to improve the physical conditions in the river system. In the main river as well as in the tributaries, barriers have been removed: previously, people built dams and stream crossings for roads prevented fish from migrating upstream. Where it had been straightened out, natural bends in the river were restored, its meanders given back and new spawning beds of gravel were established.
Bigger than average fish
The River Karup sea trout stay longer in the sea before returning to spawn compared to most sea trout found in other rivers. Fish tagging has shown that after having left the river as smolts, the majority of the sea trout from the River Karup leave the fjord and migrate to feeding areas as far away as the northern part of the Baltic Sea. This may be part of the explanation for the river’s truly unique type of sea trout which is known for being short, fat, and heavy. Many of the very big sea trout caught in River Karup have returned several times to spawn in the river.
Record sea trout
Denmark's biggest rod caught sea trout weighed 14.4 kilos (31½lbs) and was caught in River Karup by Kristian Plejdrup in 1939. It stood as a world record for decades. Mr. Plejdrup’s majestic fish was stuffed and it is displayed at the Trevad Trout Park Hatchery.
In 1991, a sea trout of 16.3 kilos (almost 36lbs!) measuring 108 centimeters was found dead in the River Karup. This giant fish had left the river as a smolt when it was two years old. It had spawned once prior to its final run up the river and had spent a total of 6-7 years in the sea.