SEA LICE LEVELS HIGH IN PARTS OF NORWAY

Sea lice levels high in parts of Norway. There are so many sea lice on wild fish in Western Norway and Central Norway that it probably has negative effects on survival in many areas.

This is stated in this year’s first report from the monitoring of sea lice on wild salmonids.

“At the start of the monitoring, it looked like there might be fewer lice this year, but as the fieldwork progressed, the number of salmon lice on the trawl-caught salmon increased,” says Ørjan Karlsen, head of salmon lice monitoring at HI in Norway.

Salmon farming has resulted in more lice

Sea lice are a natural parasite on salmonids. The large number of farmed salmon means that the number of hosts has also increased, thus the number of lice has also increased. Sea lice that originate from lice on farmed fish are transported around with the current until they reach the stage where they infect fish. They are found both in the fjords and along the coast.

The sea lice feed on the fish skin. If the fish is very small such as smolt, or has very many lice, it can eventually develop large wounds. These in turn make it more susceptible to disease in addition to general debilitation, and in the worst case, it dies. Researchers are therefore monitoring sea lice on wild salmonids.

Seeing no improvement despite many measures

Wild salmon are particularly vulnerable to sea lice in spring/early summer when the young fish (salmon smolts) swim from the rivers where they have spent the first years of their lives and out into the nursery areas in the sea.

“To get to the nursery areas, they have to swim through the areas with salmon farming,” says Karlsen.

At this time, the fish is still small, often around 20 grams, and therefore cannot tolerate getting very many lice on them.

If there are few lice in the fjords and along the coast during the period when salmon smolts migrate, they can get out to sea with little lice.

“Unfortunately, it has been many years since this last happened. Despite the fact that a number of measures have been implemented by industry and the authorities, we do not yet see any clear improvement. Lice infection on salmon naturally varies in the fjords we have studied. The results from this year are probably even a notch worse than in recent years, probably very few salmon smolts have made it through the lice belt uninfected, says Karlsen.

Sea trout live among the lice all summer

Sea trout are also exposed to salmon lice. Unlike salmon, sea trout stay in fjord and coastal areas throughout the summer. This makes it even more vulnerable to sea lice than wild salmon that “only” swim through the lice belt.

“Unfortunately, the amount of lice that we are seeing now means that this is likely to severely affect sea trout. This seems to apply to the vast majority of the areas studied in Western Norway and Central Norway,” says Karlsen.

Has trawled in Nordfjord for the first time in several years

The field surveys carried out in connection with the monitoring of salmon lice are carried out every year using the same methods. Most of the areas being investigated are also fixed, but new this year is that trawl surveys have been carried out in Nordfjord for the first time in several years. In total, more than 1000 emigrating post-smolts of salmon have been caught in Nordfjord and the Sognefjord. Preliminary analyses indicate that there were relatively large numbers of lice in both of these fjords.

About the monitoring

The Norwegian Food Safety Authority and the Ministry of Trade, Industry and Fisheries (NFD) are commissioners for HI’s monitoring programme for salmon lice on wild salmonids (NALO). The monitoring is carried out in cooperation with NINA and NORCE.

Published: 23.06.2023 Updated: 26/06/2023 Written by: Beate Hoddevik

Photo courtesy: Institute of Marine Research

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