Acronym NA
Category
Aquaculture
Title Kunnskapsoppsummering-lakselus og effekter på sjøørret - Knowledge summary: Salmon lice and effects on sea trout Programme National Programme
Instrument (FP6)
Contact Type (FP7)
Strand (Interreg)
NA
Theme (FP7)
Activity Area (FP6)
Regional Area (Interreg)
Action (COST)
NA
Specific Programme (FP7)
NA
Funding source National Coordinator Bengt Finstad Coordinator email bengt.finstad@nina.no
Coordinator institution
NINA - Norwegian Institute for Nature Research (Norway)
Institutions involved
NA
Start year 2013 End year 2014 Funding (€) € 94,667 Website https://www.fhf.no/prosjekter/prosjektbasen/900950/ Summary Salmon lice are an external parasite on salmonids in the sea. Farmed salmon can also be hosts for salmon lice, and open cages with farmed salmon therefore contribute to increased production of salmon lice in coastal areas. The purpose of this report is to summarize knowledge about the effects of salmon lice on sea trout based on a review of international scientific publications in journals and books with peer review. References to so-called "gray literature", such as technical reports, are to a small extent included. The studies that have been reviewed include everything from laboratory and field studies of effects on individual fish to studies of stock effects. Salmon lice eat the host fish's mucus, skins and tissues and cause wounds and tissue damage. Laboratory and field studies have shown that salmon lice can cause imbalances in the fish's osmoregulation (ie salt balance), physiological stress, anemia, reduced appetite and growth, increased vulnerability to secondary infections, reduced disease resistance and increased risk of mortality in sea trout individuals. Sea trout in farmed areas generally have low levels of salmon lice. In farmed areas, the level varies considerably between different surveys and areas, from low levels comparable to farmed areas to such high levels that they involve a risk of significantly increased mortality caused by salmon lice. Several studies have shown higher salmon lice levels in wild sea trout near fish farms compared to further afield. This is particularly prominent in areas closer to fish farms than 30 km. Among salmonids, sea trout are particularly vulnerable to salmon lice because they stay close to the shore during their entire sea stay, in the same type of areas as the fish farms are often located. Based on the studies that have been reviewed, it can be concluded that salmon farming leads to an increased number of salmon lice in the sea, and that despite measures that are routinely implemented, wild sea trout stocks in intensive farming areas have been negatively affected by salmon lice with reduced growth and increased mortality in the sea. The reduction in wild sea trout populations due to salmon lice can in most cases not be quantified due to a lack of comprehensive field data and studies of stock effects. Stock effects of salmon lice have been quantified in salmon by comparing growth and survival in the sea in groups of exposed fish that have been chemically protected against salmon lice with unprotected control fish. There are few such studies in sea trout, but the results for salmon indicate that on average 12–44% fewer spawning fish are potential levels of extra mortality as a result of salmon lice in farmed areas. Studies in salmon probably represent the minimum estimate for mortality in sea trout at the same localities, because salmon smolts migrate quickly through coastal areas on their way to the breeding areas in the sea, while sea trout remain in the coastal areas throughout their stay. Salmon lice do not increase the risk of trout becoming extinct as a species, but lice can change the life history strategy of sea trout. Since only part of the trout migrates to the sea, reduced growth and survival will reduce the benefits of sea migration, and may thus result in selection against sea migration in areas with high lice levels. In extreme cases, such selection can mean that the life story strategy of sea migration disappears locally. Stocks that exploit small streams and rivers with unstable environmental conditions during parts of the year, and which are thus dependent on being in the sea to survive through such periods, are particularly vulnerable. For larger watercourses with stable conditions for trout throughout the year, there is a smaller risk of loss of trout. However, a significant reduction or loss of migrating individuals may result in reduced future recruitment. Loss of growth opportunities for trout in the sea and reduced recruitment for spawning can in total lead to reduced production of trout, and that there are fewer large individuals who are often the target for fishermen. Such individuals also make large contributions to egg deposition in the population. Effects of salmon lice can also lead to a change in genetic composition and diversity among sea trout, and that sea trout stocks can be changed to become more freshwater stationary. Monitoring of wild populations indicates that such changes have already taken place in some watercourses in aquaculture-intensive areas. However, the lack of comprehensive long-term monitoring of sea trout stocks and studies of the stock effects of salmon lice means that it is often difficult to draw such concrete conclusions. The theme for the professional final report is the effects of salmon lice on sea trout, but sea trout stocks are also affected by other man-made influences. There is local and regional variation in the significance of different influencing factors, and the status of sea trout varies within the distribution area. Other man-made influencing factors include climate effects, pollution, overfishing, and diseases caused by viruses, bacteria, fungi and other parasites. Some of these impacts can be linked to increased farming activity, hydropower production and other river regulations, migration barriers and habitat changes. Effects of interaction between two or more such influencing factors can be complex and unpredictable. For sea trout stocks that are exposed to negative man-made influences in both freshwater and the sea, there is a need for coordinated measures.
Keywords
Fish;
Cage aquaculture;
Salmon;
Trout;
Open sea aquaculture;
Parasite;
Marine Region
76
Not associated to marine areas
0
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