Hindrer Nordhordlandsbroen smoltens utvandring?

Den dramatiske nedgangen av laksebestanden i Vosso har brakt flere institusjoner sammen for å undersøke betydningen av menneskeskapte forhold for denne utviklingen. De siste årene har søkelyset i hovedsak vært rettet mot lakselus og andre faktorer som kan påvirke smoltutvandringen. Havforskningsinstituttet har undersøkt hvilken betydning Norhordlandsbroen kan ha

Possible influence of salmon farming on long-term resident behaviour of wild saithe (Pollachius virens L.)

-The culture of Atlantic salmon is one of the most developed aquaculture industries in the world. The production from smolt to market size usually takes place in sea cages in open waters, and these structures tend to attract wild fish, as they do for other farmed species. For salmon farming, saithe (Pollachius virens) is one of the most-frequently observed species around sea cages. An important question is whether the large concentration of salmon farms in some areas might alter the natural behaviour and migration pattern of wild saithe. We tagged 62 wild saithe with acoustic tags and followed their movements for up to 2 years in an area in Southwestern Norway with many salmon farms. Furthermore, nearly 2000 saithe were tagged with external T-bar tags to study migration beyond the study area. The recaptures of the T-bar tagged saithe from offshore areas suggest that the offshore migration routes of saithe are similar to published results from before salmon farming became significant in the area. However, a large proportion of the saithe population appears to remain in the release area and was observed at the salmon farms for much of the time. We conclude that the aquaculture industry is influencing the local saithe distribution. Large-scale population effects are more difficult to prove, but it is possible that the dynamic relationship between the coastal and oceanic phases has been altered

Effects of pre-release acclimatization period on salmon return rates

42.000 1+smolts of Atlantic salmon were size graded into two size groups and released during three weeks in spring 1993; one group of small and one of large smolts on each of the four release days. Approximately 25% of the fish had been individually tagged using Carlin-tags. The fish were transferred to net pens in a small marine bay in which estuarine salinity gradients had been established by a tarpaulin barrier. The smolts were held in the net pens for three days prior to the first and third release day and seven days before the second and fourth release day. Total recoveries of Carlin-tagged grilse in 1994 showed higher return rates for smolts acclimatized for three days compared with seven days. The difference was small for large smolts, but significant for small smolts, as return rate for the three days acclimatization was twice that of seven days acclimatization. The retum of precocious mature males, males that were mature prior to release, were clearly higher than that of other smolts. Possible causes for these differences are discussed

Vekstmønster hos laksepar - styring og konsekvenser

Sluttrapport for NFFR-prosjekt 1402-V 701.29

Hindrer Nordhordlandsbroen smoltens utvandring?

Den dramatiske nedgangen av laksebestanden i Vosso har brakt flere institusjoner sammen for å undersøke betydningen av menneskeskapte forhold for denne utviklingen. De siste årene har søkelyset i hovedsak vært rettet mot lakselus og andre faktorer som kan påvirke smoltutvandringen. Havforskningsinstituttet har undersøkt hvilken betydning Norhordlandsbroen kan ha

Impact of early salmon louse, Lepeophtheirus salmonis, infestation and differences in survival and marine growth of sea-ranched Atlantic salmon, Salmo salar L., smolts 1997-2009

The impact of salmon lice on the survival of migrating Atlantic salmon smolts was studied by comparing the adult returns of sea-ranched smolts treated for sea lice using emamectin benzoate or substance EX with untreated control groups in the River Dale in western Norway. A total of 143500 smolts were released in 35 release groups in freshwater from 1997 to 2009 and in the fjord system from 2007 to 2009. The adult recaptures declined gradually with release year and reached minimum levels in 2007. This development corresponded with poor marine growth and increased age at maturity of ranched salmon and in three monitored salmon populations and indicated unfavourable conditions in the Norwegian Sea. The recapture rate of treated smolts was significantly higher than the controls in three of the releases performed: the only release in 1997, one of three in 2002 and the only group released in sea water in 2007. The effect of treating the smolts against salmon lice was smaller than the variability in return rates between release groups, and much smaller that variability between release years, but its overall contribution was still significant (P<0.05) and equivalent to an odds ratio of the probability of being recaptured of 1.17 in favour of the treated smolts. Control fish also tended to be smaller as grilse (P=0.057), possibly due to a sublethal effect of salmon lice

Experiences with recapture of escaped farmed salmon in Norway

Monitoring and statistics of the amount of escaped salmonids in the sea in Norway is limited. Recapture is encauraged in several counties by allowing a sea fishery targeting escapees from 1. October to 28. February. Low recapture rates have generally been obtained following large escape events. Telemetry studies of the post-release behaviour of cultured salmon in the Hardanger Fiord have shown 1)that the salmon dive frequently the first days after escape, 2) but then move close to the surface the next weeks. and 3) that they spread rapidly. The recapture effort should preferably cover a large area for at least 4-5 weeks and not be limited to the vicinity of the fish farm. NORSK SAMMENDRAG: Overvåking og statistikk over mengden rømt oppdrettslaks i sjøen i Norge er mangelfull. Gjenfangst av rømt fisk er i flere fylker organisert ved å tillate et generelt fiske etter rømt fisk fra 1. oktober til 28. februar.Gjenfangstfiske etter større rømmingsepisoder har generelt gitt lave gjenfangster. Pågående telemetristudier av adferden tii simulert rømt laks i Hardangerfjorden har vist 1) at laksen dykker etter rømming, 2) at den trekker opp mot overflaten etter noen dager, men 3)at den da allerede har spredd seg utover et stort område. Gjenfangst bør ikke begrenses til rømmingslokaliteten, men spres over et stort areal og kan opprettholdes i minst 4-5 uker

Estimating the temporal overlap between post-smolt migration of Atlantic salmon and salmon lice infestation pressure from fish farms

To be able to design effective management to alleviate wild fish from parasite infestation pressure from fish farms, it is pivotal to understand when post-smolts migrate past areas of potential exposure to salmon lice Lepeophtheirus salmonis. Here, data from release groups of coded-wire-tagged Atlantic salmon Salmo salar smolts and their subsequent recaptures in a trap net in the outer fjord 12 to 97 km from the various release sites were used to estimate the smolts’ progression rate and their arrival time in an outer fjord in Norway. The arrival time estimates to the outer fjord are compared with modelled infestation pressure from local fish farms. The overall progression rate varied from 0.8 to 31.2 km d-1 (0.05 to 2.20 body lengths s-1), with mean and median values of 8.8 and 7.8 km d-1, respectively (0.60 and 0.54 body lengths s-1). The progression rate varied with water discharge from the rivers into the fjords, fish length, condition factor and smolt origin. Simulated arrival time and capture of wild smolts suggest that smolts from the different rivers arrive in the outer fjord system with a difference of up to 4 wk. The arrival time for the rivers with the longest migration was estimated to be from mid-May throughout June. Infestation pressure from fish farms increased from the beginning of June in 2 of 3 study years, suggesting that an increase in lice exposure from fish farms will overlap with smolts from late-migrating populations in some but not all years

Impact of parasites on salmon recruitment in the Northeast Atlantic Ocean

Parasites may have large effects on host population dynamics, marine fisheries and conservation, but a clear elucidation of their impact is limited by a lack of ecosystem-scale experimental data. We conducted a meta-analysis of replicated manipulative field experiments concerning the influence of parasitism by crustaceans on the marine survival of Atlantic salmon (Salmo salar L.). The data include 24 trials in which tagged smolts (totalling 283 347 fish; 1996-2008) were released as paired control and parasiticide-treated groups into 10 areas of Ireland and Norway. All experimental fish were infectionfree when released into freshwater, and a proportion of each group was recovered as adult recruits returning to coastal waters 1 or more years later. Treatment had a significant positive effect on survival to recruitment, with an overall effect size (odds ratio) of 1.29 that corresponds to an estimated loss of 39 per cent (95% CI: 18-55%) of adult salmon recruitment. The parasitic crustaceans were probably acquired during early marine migration in areas that host large aquaculture populations of domesticated salmon, which elevate local abundances of ectoparasitic copepods-particularly Lepeophtheirus salmonis. These results provide experimental evidence from a large marine ecosystem that parasites can have large impacts on fish recruitment, fisheries and conservation