Årbok 2013

Sea lice as a problem for wild salmon and sea trout

Foredrag på NTVA-møte i Trondheim 15. oktober 2013

Atle Kambestad, Seniorrådgiver, Miljødirektoratet

Norway is the most important area for North Atlantic salmen. holding approximately 465

different stocks of this species. Salmen contribute a streng cultural, recreational and

economic value. More than 100 000 anglers fish salmen each year, trailing about 1.4 billion

NOK in value. An additional 1000 professiona'l fish salmen in the sea.

The most important information for the authorities is given by the Norwegian ScientifiC

Advisory Committee for Atlantic Salmen Management. They calculate the annual number of

spawners returning from the ocean to Norwegian rivers. This has declined the resent years,

from about 1 million in the mid 1980's, to about 400 000 the past years. The most important

reason for the decline the latest years is low sea survival, but there are also several other

important factors. There are regional differences in !his development. The largest decline in

returning spawners is in the west region, where the aquaculture is !argest.

Escaped, farmed salmen is the most common negative factor on wild-stock salmen,

according to the official Norwegian salmen stock register. Sea lice is the second most

common factor. Historically there have been five important factors with great impact on the

Norwegian salmen stocks. Acidification and hydropower plants started as a problem for the

salmen and sea trout in the late 1900's, and '"ere at their strengest from about 1950 to 1990.

Later several acts have reduced their impact. lndustrial pollution from Europe that resulted in

acidification from rain, has also been reduced. The parasite, Gyrodactylus salaris, was

introduced in the 1970-ties, bul has new bee111 removed from most of the infected rivers. We

are !hen left wilh two faclors !hal are not u,der control; sea lice and escapees of farmed

salmen. Both of them from the salmen fanming industry. These factors can make further

damage in the future.

In areas with most dense salmen farming, sea lice is already responsible for severe mortality

of sea traut and wild salmen. The Institute

Marine Research has calculated the mortality

on sea trout and salmen to be as high as 50 - 90

in some of the worst regions. These

levels are a potential risk of extermination of some of the stocks,

maintained in the future.

In two salmen stocks in western Norway,

th~

measured leve! of increased mortality due to

sea lice is 15

measured in the past 15 years. This reduces the surplus for angling,

and might cause the river fishing to be closed. In the county with most salmen farming,

Hordaland, most of the salmen rivers and many of the sea trout rivers are already closed. All

salmen fishing with nets in the sea has been banned in this county, as the only one in

Norway. The situation of salmen and sea trout in Hordaland is by far more serious than in the

other regions in Norway.

The amount of sea lice on each farmed salmon has been reduced much the latest 15 years,

due to acts from the Norwegian Food Safety Authority. Bul the total number of sea lice is still

high, because of the great growth in the salmen farming industry. There are now at least

1200 times more farmed salmen than wild salmen in Norway. Some new and improved

treatments against sea lice in the farms are being developed, but in a short term the big

concern is sea lice developing resistance against the most important, chemical treatments.