Humpback salmon
The humpback salmon is originally native to the Pacific Ocean. It is an alien salmon species that is establishing itself in Norwegian rivers and the Atlantic system.
Humpback salmon
The humpback salmon is an alien species in Norway, originally native to the Pacific Ocean, the Bering Sea and northern parts of Asia and North America. It is anadromous, meaning it spawns in freshwater, but lives most of its life in the sea. The species was first observed in Norway in 1960, particularly in Troms and Finnmark.
The humpback salmon is the smallest of the Pacific salmon. The male develops a humpback and a hook on the upper jaw during spawning, and both sexes die shortly after spawning. It has a fixed two-year life cycle. In Norway, it spawns mainly in August, often in lower river sections with gravel and good water flow.
The fry hatch before Christmas and remain in the substrate until spring before migrating into the sea as smolts. The species lives in schools, has a slender body shape and feeds pelagically on crustaceans and fish. Mature fish usually weigh around 2 kg. In Finnmark, migration occurs from mid-June to early August, with spawning in August to early September.
Establishment and development
Humpback salmon were first recorded in Norwegian rivers in 1960, particularly in Finnmark and Nord-Troms. Early observations and catches coincide with Russian releases on the Kola Peninsula from 1956, which were successful from 1959. Large quantities of fertilized eggs were retrieved from the Pacific Ocean (Sakhalin and the Kuril Islands), and new releases from Magadan and Kamchatka in the 1980s gave particularly good results in 1985. This led to self-reproducing populations in the Umba River at the White Sea. Subsequent generations were bred locally, and sustainable populations developed in the Barents Sea area.
The influx to the Norwegian coast increased in the 1970s, but catches were variable until 2015. From 2017 there was a sharp increase in the number of rivers with humpback salmon and in total catches. In 2021, the species was observed in 271 Norwegian rivers. Although the numbers were often low, there was a high increase in many rivers. Despite withdrawal measures, humpback salmon have spawned in a number of rivers, and natural recruitment (eggs and fry) has been documented in many watercourses, especially in Finnmark, but also in Troms, Nordland, Trøndelag and Vestland.
It is uncertain how much of the migration is due to Norwegian stocks and how much comes from Russian rivers. Genetic documentation of return to Norwegian rivers is lacking. Nevertheless, developments indicate that there are self-reproducing stocks in Norway, probably established from around 1989. The humpback salmon has established itself as an invasive species with potential for further growth and spread.