The deadly parasite

Sea lice - a threat to wild salmon

Sea lice - lethal to wild salmon and sea trout

More than 1000 fish farms, positioned along the Norwegian coast, hold continually more than 300 million salmon in their pens. In comparison, the total numbers of wild salmon returning to Norwegian rivers are between 0.5 and 1.0 million.

Sea lice occur naturally in sea water and prior to fish farming, were not of any significant threat to wild salmon, sea trout and arctic char. However, because of the enormous numbers of salmon and rainbow trout held in fish farms throughout the year, an abnormally high sea lice concentration has developed in fjords and coastal areas where there is fish farming. Fish that escape from the fish farms add to the spread of sea lice.

When smolts leave their rivers and migrate to the oceans to feed they pass numerous fish farms on their way. If the farmed fish areas contain extensive numbers of sea lice during the spring and early summer the smolts have to make their way through a significant concentration of sea lice.

This can be lethal to the young fish. Sea lice attach themselves to the skin and large numbers of smolt die due to lesions and infections. Some areas on the west coast of Norway have experienced up to 95% fatality of migrating smolt due to sea lice.

Resistant sea lice are a threat to the wild salmon

Chemical treatments are mainly used to contain the populations of sea lice in fish farms. Some remedies are mixed with the fish feed while others are placed directly in the water in the pens. Major concern has arisen as in parts of the fish farming areas the sea lice have become resistant to treatment. This situation is bound to increase in severity if resistant sea lice continue to spread to new fish farms further afield. Without effective treatment, the sea lice population is set to explode. If this happens it will have grave consequences for the wild salmon and sea trout stocks in Norway

Sea lice

Sea lice (Lepeophtheirus salmonis) are parasites that exist on slime, skin and blood from salmonoids. Sea lice only survive when the host is in salt water. Lice have always existed
naturally on salmon, sea trout and arctic char without
being any lethal threat to the wild fish.

New action and increased effort against sea lice

The threat against wild salmon and sea trout stocks is
already very serious. With increased resistance to treatment and the increasing number of fish farming licences, the sea lice situation can turn out to be dire. The Government should, with no time to lose, implement all actions that the strategy for sustainable aqua culture puts forward. The Norwegian Association of Hunters and Anglers, Norwegian Salmon Rivers og World Wildlife Fund - Norway are in joint agreement about the demand for increased action against sea lice:

• Licensing for new fish farms for salmon and trout should
  stop until a new and dedicated action plan to fight the sea
  lice is planned and implemented.
• Fisheries and Environment authorities should secure a
  substantial and continuing surveillance of sea lice populations on wild salmon and sea trout.
• When there is a damaging level of sea lice on wild salmon
  and sea trout in any coastal or fjord area, immediate action
  should be taken to delice and abandon fish pens.
• The use of giant pens that prevent effective sea lice counts
  and direct sea treatment should be banned.
• There should be an evaluation of the need to extend national salmon fjords in order to secure migrating corridors and sharpen up administration processes.

Related:

• Resistant SEA-LICE threatening wild salmon stocks along the Norwegian coastline