Increasing numbers of lice

In Hardangerfjorden, sea lice infection rates increased in June in relation to May, particularly on sea trout in the outer part of the fjord. An increase in sea lice levels was also observed in Herdlefjorden (Hordaland) and off Namsenfjorden (Trøndelag). In the other fjord systems studied, results show that sea lice levels on wild salmonids remain low.

By Beate Hoddevik Sunnset

The current situation, with few sea lice in the spring followed by a slight increase at the start of June, is reminiscent of 2009, and is described in a preliminary report sent by The Institute of Marine Research to the The Norwegian Food Safety Authority today. Last year there was a significant increase in sea lice infection rates over the summer and autumn, and it is possible that the same will happen this year. Rising sea temperatures result in greater numbers of sea lice, as egg production increases when it is warmer. Currents in the fjords and along the coast can also affect the situation, although it is uncertain how big an impact they have.

Delayed smolt

Salmon smolt migrate out of the fjord in the spring, and during the migration they can be attacked by lice. The exact timing of the smolt migration depends on factors such as the water temperature and freshwater discharge into the fjord, and this year it appears that the migration will take place somewhat later than last year in a number of rivers, which means that the salmon smolt may not get out of the fjord systems by the time sea lice concentrations increase. (mener laksen kom seg ut ok?). Sea trout stay in the fjords throughout the summer, and may therefore face problems if lice numbers increase.

Monitoring the national salmon fjords

The Institute of Marine Research has been tasked by The Norwegian Food Safety Authority and the Ministry of Fisheries and Coastal Affairs with coordinating the monitoring of sea lice infection rates in wild salmonids, particularly in the most important national salmon fjords. This is being done in collaboration with the Norwegian Institute for Nature Research (NINA) and consultant biologists from Rådgivende Biologer AS.

This year the programme's field work will be carried out from the middle of May until the middle of August at selected locations along the length of the Norwegian coast. The report that has been sent to The Norwegian Food Safety Authority today contains preliminary data from the first monitoring period (10 May-10 June), covering the section of the coast from Hardangerfjorden in the south to Namsenfjorden in the north. The data are based on preliminary observations/counts carried out in the field. The final report will be produced in late autumn/winter 2010.

Facts about sea lice

Latin name: Lepeophtheirus salmonis
Distribution: occur naturally in Norwegian waters. Their numbers have risen significantly in parallel with the growth of the aquaculture industry.
Biology: sea lice are parasites with ten life stages, three of which are free-swimming, four of which are stationary and three of which are mobile. They attach themselves to salmon in the third life stage.
Size: adult female: 12 mm (approx. 29 mm including egg strings); adult male: 6 mm.
Diet: the skin and blood of salmonids. The lice only start feeding when they have attached themselves to a host fish (stationary and mobile stages).
Reproduction: all year round, but reproduce increasingly quickly as temperatures rise in spring.
Dispersal: free-swimming stages spread on currents in fjords and coastal waters.
Treatment: biological methods (wrasse) or chemicals (medication).