September

Humpback salmon. Photo: Henrik Hårdensson Berntsen, NINA

Unwanted competitors on the spawning ground

A colder breeze in the air signals that fall is approaching. The salmon begin to dress in their spawning costumes and line up at the spawning grounds. There is still a while to go before they spawn, but in many rivers there are already fertilized salmon eggs in the river gravel. These are eggs that shouldn't even be there. The parents are a species of Pacific salmon, namely pink salmon.

Humpback salmon is a foreign species that was introduced into watercourses on the Kola Peninsula in the late 1950s. Unfortunately, it has now found its way to Norwegian rivers and is spawning here. In an increasingly large part of Norway, there are many pink salmon.

Humpback salmon can bring diseases and parasites with them, and they can wreak havoc on wild salmon, sea trout and char. Humpback salmon prefer some of the same spawning grounds as our wild salmon, sea trout and char, but they spawn earlier. We know that humpback salmon that are about to spawn are very aggressive. Local salmon fishermen therefore choose to stay away from places where they would normally be.

The juvenile pink salmon, which hatch in early spring, are in a hurry to get to the sea. They only stay in the river for a few weeks before leaving. Humpback salmon fry can be numerous and have a good appetite during their short time in the river. Humpback salmon fry that have hatched far upstream in a river, in particular, can feed heavily on the wild salmon fry on their journey out.

The invasion of pink salmon was particularly large in 2021. Never before have larger quantities been recorded. The rivers in the north of the country were particularly hard hit. We know little about what consequences this will have.

Tanalaks in search of spawning grounds. Photo: Mikko Kytokorpi.