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Bergen, Norway

Thorstad E.B.,Norwegian Institute for Nature Research | Todd C.D.,University of St. Andrews | Uglem I.,Norwegian Institute for Nature Research | Bjorn P.A.,Norwegian Institute of Marine Research | And 6 more authors.
Aquaculture Environment Interactions | Year: 2015

Salmon farming increases the abundance of salmon lice, which are ectoparasites of salmonids in the sea. Here we review the current knowledge on the effects of salmon lice on wild sea trout. Salmon lice feed on host mucus, skin and muscle, and infestation may induce osmoregulatory dysfunction, physiological stress, anaemia, reduced feeding and growth, increased susceptibility to secondary infections, reduced disease resistance and ultimately mortality of individual sea trout. Wild sea trout in farm-free areas generally show low lice levels. In farm-intensive areas, lice levels on wild sea trout are typically higher, and more variable than in farm-free areas. Lice on wild sea trout are found at elevated levels particularly within 30 km of the nearest farms but can also extend to further ranges. Salmon lice in intensively farmed areas have negatively impacted wild sea trout populations by reducing growth and increasing marine mortality. Quantification of these impacts remains a challenge, although population-level effects have been quantified in Atlantic salmon by comparing the survival of chemically protected fish with control groups, which are relevant also for sea trout. Mortality attributable to salmon lice can lead to an average of 12-29% fewer salmon spawners. Reduced growth and increased mortality will reduce the benefits of marine migration for sea trout, and may also result in selection against anadromy in areas with high lice levels. Salmon lice-induced effects on sea trout populations may also extend to altered genetic composition and reduced diversity, and possibly to the local loss of sea trout, and establishment of exclusively freshwater resident populations. © The authors 2015. Source

Skaala O.,Norwegian Institute of Marine Research | Johnsen G.H.,Radgivende Biologer AS | Lo H.,Norwegian Veterinary Institute | Borgstrom R.,Norwegian University of Life Sciences | And 5 more authors.
Marine Biology Research | Year: 2014

Extensive use of aquatic habitats, mainly for hydropower and aquaculture, has a negative impact on anadromous salmonid populations of the Hardangerfjord region, western Norway. High infection levels of salmon lice, and high proportions of escaped farmed salmon in spawning rivers, appear to violate the goals in the 'Strategy for an Environmentally Sustainable Aquaculture Industry' set by the Norwegian government. An overview of the anadromous populations in the fjord, their status and the major threats are presented. A conservation plan with mitigation efforts consisting of seven steps is presented: (1) genetic assessment of Atlantic salmon and anadromous brown trout populations, (2) reducing gene flow from escapees, (3) reducing infection pressure from salmon lice, (4) conduct an assessment of the freshwater habitats for anadromous salmonids and then implement it in order to restore smolt production, (5) efforts to reduce risk of river pollution from agriculture and industry and minimize impacts from hydropower production, (6) when and where necessary and practical, plant out eyed eggs from the Norwegian Genebank to increase parr and smolt production, and finally, (7) monitor spawning populations and parr densities to evaluate potential effects of the mitigation efforts. Experience and knowledge gained through the plan will be useful for other regions with similar challenges. We call for an initiative to establish a national fund under democratic and public control, where funding can be obtained for projects which focus on mitigation efforts and conservation of salmonid populations. © 2014 The Author(s). Source

Thorstad E.B.,Norwegian Institute for Nature Research | Todd C.D.,University of St. Andrews | Uglem I.,Norwegian Institute for Nature Research | Bjorn P.A.,Norwegian Institute of Marine Research | And 6 more authors.
Marine Biology | Year: 2016

An understanding of when and where sea trout Salmo trutta L. are located at sea is essential to the effective management of local populations and in evaluating their vulnerability to salmon lice and other anthropogenic threats. Here we review the available literature on sea trout life-history strategies, behaviour and habitat use in the marine environment, including feeding, growth, survival and homing. There is considerable variation in life-history strategies among individuals and populations and in the timing and duration of marine migration(s). Females tend to adopt the anadromous strategy more than do males. Smolts typically leave rivers in spring (March–June in European rivers), but also at other times of the year. Post-smolts may remain at sea during the summer and return to freshwater to over-winter; adults thereafter spend summers at sea and winters in freshwater, or they can remain at sea until they later return to freshwater for spawning. Sea trout frequently are recorded at sea during winter and can tolerate full-salinity sea water at water temperatures as low as 1–2 °C. Sea trout often remain within 80 km of their river of origin, but also may undertake longer-distance marine migrations (>500 km). The duration and timing of marine migration both are likely governed by trade-offs between mortality risk and growth potential in different habitats, and the most beneficial strategy may vary among individuals and populations. Reduced marine growth and increased marine mortality will reduce the benefit of marine migrations and may result in selection against anadromy. © 2016, Springer-Verlag Berlin Heidelberg. Source

Glover K.A.,Norwegian Institute of Marine Research | Glover K.A.,University of Bergen | Bos J.B.,Norwegian Institute of Marine Research | Urdal K.,Radgivende Biologer AS | And 8 more authors.
Biological Invasions | Year: 2016

Each year, hundreds of thousands of farmed Atlantic salmon escape from fish farms into the wild. Some of these escapees enter freshwater, and manage to interbreed with native populations. To hinder further genetic introgression in native populations, the use of sterile triploid salmon within commercial aquaculture is being examined. However, if triploid escapees migrate into freshwater, they may still have ecological impacts on local populations. In the present study, we used microsatellite DNA genotyping to determine the ploidy of 3794 farmed escapees captured in 17 Norwegian rivers in the period 2007–2014. Although a previous study has reported an average of 2 % triploids in Norwegian fish farms during this exact period, here, we only observed 7 (0.18 %) triploids among the escapees captured in freshwater. In addition, we identified three trisomic escapees. For the triploids where the within-river capture location was determined, they were only observed in the lower reaches and not on the spawning grounds. It is concluded that propensity for triploid Atlantic salmon to migrate into freshwater following escape from a fish farm is significantly lower than for normal diploid salmon escapees. Therefore, commercial production of triploids should not only be seen as an effective way of stopping genetic introgression, it will also significantly reduce the numbers of escapees entering rivers, which in turn limits ecological interactions and potential disease transmission. © 2016 The Author(s) Source

Arechavala-Lopez P.,Norwegian Institute for Nature Research | Arechavala-Lopez P.,University of Alicante | Thorstad E.B.,Norwegian Institute for Nature Research | Todd C.D.,University of St. Andrews | And 8 more authors.
Revista de Biologia Marina y Oceanografia | Year: 2015

Salmon lice are external parasites on salmonids in the marine environment. During recent years, sea lice abundance has been increased due to the presence of salmon farming using on-growing floating seas-cages. Amongst salmonids, sea trout is especially vulnerable to salmon lice infestations, because during their marine residence they typically remain in coastal waters, where open net cage Atlantic salmon farms typically are situated. In this report the existing knowledge about the effects of salmon lice on sea trout populations in the NE Atlantic coastal waters has been reviewed, assessing the current situation of this problematic. Salmon aquaculture increase the salmon lice abundance, which affect negatively on sea trout populations as an increase in marine mortality, changes in migratory behaviour and reduction of marine growth. These conclusions are based on published studies that range from those investigating the effects of salmon lice on individual fish, both in the laboratory and the field, to analyses of their impacts on populations in the wild. In sum, the combined knowledge from the reviewed studies provides evidence of a general and pervasive negative effect of salmon lice on sea trout populations, especially in intensively farmed areas. The effects induced by elevated salmon lice levels inevitably imply a reduction in numbers and body size of sea trout returning to freshwater for spawning, affecting the local population dynamic and recreational and commercial fisheries in the most impacted areas. © Universidad de Valparaiso. All rights reserved. Source

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