Salmon lice infection on wild salmonids in marine protected areas: an evaluation of the Norwegian ‘National Salmon Fjords’

Abstract

In Norway, 29 fjords and 52 rivers have been designated for protection in order to prevent the infection of important populations of wild salmonids with salmon lice of farm origin. We evaluated the effect of this protection on the lice infection pressure for wild salmonids based on lice counts performed on wild-caught sea trout and Arctic charr inside onethird of these protected fjords (known as 'National Salmon Fjords'). Results indicate that these areas may provide a certain extent of protection against lice of farm origin, but their configuration will play a key role in their success. When the size and shape of a protected area are such that fish farms are kept at a minimum distance (calculated here as at least 30 km, but this distance is likely site-dependent), wild fish seem unaffected by the direct lice infection pressure imposed by fish farms. In contrast, the effects of small protected fjords were strongly dependent on the production pattern of the aquaculture industry in the surrounding area, and we found a clear correlation between lice levels on wild salmonids and lice production in nearby salmon farms. To establish more precise management practices, both in National Sal mon Fjords and other fjord systems along the Norwegian coast, the development and validation of accurate distribution and abundance models for the dispersion of planktonic lice larvae is needed; this could also be the basis for an area management system based on 'maximum sustainable lice loads' or 'lice quotas.'

Salmon lice infection in wild salmonids in marine protected areas: Comment on Serra-Llinares et al. (2014)

“…Schram et al (1998) observed the same temporal pattern in lice numbers on wild sea trout Salmo trutta in areas with no salmon farming. Additionally, there seems to be a spatial component in lice abundance on wild fish, suggesting lower lice numbers in the north (Altafjord) (Serra-Llinares et al 2014). A similar spatial pattern in lice abundance was observed in farmed fish (Jansen et al 2012).…”

“…3 in Serra-Llinares et al 2014). Copepodite production in farms was estimated using the reproduction model of Stien et al (2005), with temperature as a determinant of the per capita reproductive rate per female louse.…”

“…The authors concluded that 'results from this analysis support the hypothesis of a positive correlation between production of live infective stages from fish farms and the mean abundance of lice on wild fish in surrounding areas' (Serra-Llinares et al 2014, p. 11). Serra-Llinares et al (2014) deduced that successful protection of wild salmonids in small fjords is 'strongly dependent on the production pattern of the aquaculture industry in the surrounding area' (p. 1). Here we question the design of the correlation and regression analyses presented by Serra-Llinares et al (2014) and suggest an alternative explanation for the close relationship between lice numbers in wild salmonids and adjacent salmon farms.…”

“…Serra-Llinares et al (2014) deduced that successful protection of wild salmonids in small fjords is 'strongly dependent on the production pattern of the aquaculture industry in the surrounding area' (p. 1). Here we question the design of the correlation and regression analyses presented by Serra-Llinares et al (2014) and suggest an alternative explanation for the close relationship between lice numbers in wild salmonids and adjacent salmon farms.…”

“…Serra- Llinares et al (2014) analysed the association between estimated salmon louse production in salmon farms (focusing on copepodites, the infective stage of Lepeophtheirus salmonis) and lice infection levels in the wild salmonids Salmo trutta and Salvelinus alpinus. Using correlation and regression analyses, they found that the estimated copepodite production in nearby salmon farms explained 41% of the variance in the mean abundance of lice on wild fish.…”