To spread salmon hatches-there is no doubt that the number of lice on wild fish has increased in accordance with the increase in the number of farmed fish, says researcher. Irene Mårdalen freelance journalist published on Sunday 24. November 2019-04:30
Figure 2. areas with a relatively high density of copepodites on a scale from 0-1 (Quantity per square meter).
"Sea trout in Nordhordland had more than 50 lice on average per fish. In the Sognefjord, the numbers were more than 30 lice per sea trout. The wild salmon in the Sognefjord had over 20 lice each for three out of four weeks where the fish were monitored.
Results are from the Institute of Marine Research and the Norwegian Institute of Natural Research (NINA), after they monitored sea trout and wild salmon for a period of four weeks earlier this year.
The monitoring shows, among other things, that all the fish in Bjordal had lice, and that on average they had over 30 lice each. In Balestrand, 95 per cent of the fish had lice, and they also had over 30 lice each.
On the other hand, there is little lice in southern Norway, with the exception of the sea trout in the Flekkefjord.
LITTLE LICE IN THE NORTH
In the Boknafjord, little lice were found on trawled salmon, but more lice on sea trout caught in ruse. Sea lice were found in Hardanger and Rogaland, and smaller than in 2018.
The figures show that there is generally little lice on wild fish in Northern Norway. Data from the catch of sea trout early in the season showed that there were few lice on the fish from Nordland and Troms. The same applies from Nord-Troms to Finnmark. The exception is the Altafjord, where there was little lice early in the season, but more during the summer.
FACTS ABOUT THE MONITORING OF SALMON LICE
· There are up to 400 million farmed salmon in Norway and an estimated 2.5 million wild salmon fish
· In 1992, the Norwegian Institute of Natural Research (NINA) and the Marine Research Institute started monitoring wild fish in Norwegian waters. The background was that wild fish with large amounts of lice were discovered
· Today trawlers, snags and nets are used to catch salmon and sea trout to monitor the amount of lice. In some places, a cage with farmed salmon is also used to measure the infection pressure at a particular location.
· In addition, the Marine Research Institute's salmon lice distribution model is used to estimate the amount where no physical monitoring is carried out.
· Monitoring is carried out on behalf of the Norwegian Food Safety Authority and the aim is to investigate the extent of salmon lice on wild fish as a result of the aquaculture industry
· Monitoring is carried out along the entire coast where farming is conducted.
(Sources: NINA and the Marine Research Institute)
- There is no doubt that the number of lice on wild fish has increased in accordance with the increase in the number of farmed fish. And even though the industry is very good at treating farmed fish, there are still a large number of lice larvae that spread from farms to Norwegian fjords, says senior researcher Bengt Finstad at NINA.
The aquaculture industry is increasing the number of lice on wild fish
Senior scientist Ørjan Karlsen at the Institute of Marine Research is also sure that the increase in lice on wild fish is mainly due to the aquaculture industry. This despite the fact that the aquaculture industry spends billions of dollars on reducing the number of lice in the farms.
- The growing production of the aquaculture industry has meant that we have a much larger number of farmed fish. This means that the lice have more hosts. A louse larva hatched in a plant can spread several miles into the sea and settle on a wild fish. A wild fish therefore does not need to be near a fish farm to be infected by lice, says Finstad.
Lice despite; Neither Finstad nor Karlsen believes we should reduce the number of farms, as long as this is sustainable production.
- Sustainable operations constitute an important industry and it is quite possible to have an active and good industry as the wild fish are protected, says Finstad.
Hard to get rid of lice
The aquaculture industry in Norway takes many measures against lice. Northern salmon - which produces as many as 40,000 metric tonnes of salmon and rainbow trout a year - aims to keep control of the lice.
- We take a number of preventative measures. The basic thing is production planning, where we strive for zone and coordinated set-aside of the plants, says Lars Fredrik Martinussen, communications manager at Nordlaks.
This means, among other things, that they collaborate with the neighbor breeder to clear the entire Tysfjord for fish at the same time between each release. Without salmon, the lice also disappear. In addition, they put protective skirts against salmon lice around the cages.
Other aquaculture companies also use lump fish to reduce the amount of lice. In addition, the industry is working to increase the size of the fish to reduce the time the salmon spend on reaching the slaughter weight in the sea.
The industry works with breeding to produce fish that are more resistant to salmon lice. In addition, efforts are being made to produce fish feed that will help prevent the lice from feeding on the fish.
There are also mechanical methods and medications that can remove the salmon lice from the farmed fish.
Not just lice that threaten the wild fish
Professional manager Ketil Rykhus at Sjømat Norge agrees that salmon lice in the aquaculture industry should be combated. At the same time, he is concerned that the research communities do not forget other factors that contribute to better living conditions for wild salmon.
- If the aquaculture industry is to grow, the number of lice must be reduced. At the same time, we know that - by reducing the number of salmon lice - we might just save an extra wild salmon for every 100 smolt (small salmon) that swim from the river into the sea, says Rykhus.
At the same time, he believes that the aquaculture industry should be concerned with having as little lice as possible for the sake of fish welfare.
Reference:
Rune Nilsen and others: Salmon lice infestation on wild salmon fish along the Norwegian coast in 2019 , final report to the Norwegian Food Safety Authority, September 2019
FACTS ABOUT SALMON LICE
· Parasite that settles on salmonids (salmon, sea trout and sea trout)
· The parasite eats off the fish's mucus, skin and blood
· Only live in salt water
· Fish with a lot of lice can weaken and die from damage
· A salmon lice can live for at least 15 months
· Fish with salmon lice do not taste any different than fish without lice. If the fish has lice damage, it can be downgraded
· It is not dangerous for humans to eat salmon that have had lice
https://forskning.no/fisk-fiskehelse-fiskesykdommer/slik-sprer-lakselusa-seg/1596768?fbclid=IwAR1KdDTFKoElhLdDdL4OiL0VL1MdOJOTW3lMgg8p2au7YMc8UBmbBYomm9w
https://www.hi.no/hi/nettrapporter/rapport-fra-havforskningen-2019-35
