How sea lice from salmon farms may cause wild salmonid declines in Europe and North America and be a threat to fishes elsewhere

Abstract

Fishes farmed in sea pens may become infested by parasites from wild fishes and in turn become point sources for parasites. Sea lice, copepods of the family Caligidae, are the best-studied example of this risk. Sea lice are the most significant parasitic pathogen in salmon farming in Europe and the Americas, are estimated to cost the world industry E300 million a year and may also be pathogenic to wild fishes under natural conditions. Epizootics, characteristically dominated by juvenile (copepodite and chalimus) stages, have repeatedly occurred on juvenile wild salmonids in areas where farms have sea lice infestations, but have not been recorded elsewhere. This paper synthesizes the literature, including modelling studies, to provide an understanding of how one species, the salmon louse, Lepeophtheirus salmonis, can infest wild salmonids from farm sources. Three-dimensional hydrographic models predicted the distribution of the planktonic salmon lice larvae best when they accounted for wind-driven surface currents and larval behaviour. Caligus species can also cause problems on farms and transfer from farms to wild fishes, and this genus is cosmopolitan. Sea lice thus threaten finfish farming worldwide, but with the possible exception of L. salmonis, their host relationships and transmission adaptations are unknown. The increasing evidence that lice from farms can be a significant cause of mortality on nearby wild fish populations provides an additional challenge to controlling lice on the farms and also raises conservation, economic and political issues about how to balance aquaculture and fisheries resource management.

High host densities dilute sea lice Lepeophtheirus salmonis loads on individual Atlantic salmon, but do not reduce lice infection success

“…are external parasites responsible for multi-million dollar losses in the salmon industry worldwide (Costello 2009a), and for some of the major ecological impacts associated with marine aquaculture (Krkošek et al 2007, Costello 2009b, Torrissen et al 2013. Sea lice have a multiple-stage life cycle which includes free-swimming larvae and attached moult stages.…”

The effect of temperature and fish size on growth of juvenile lumpfish (Cyclopterus lumpus L.)

“…The parasitic sea louse Lepeophteirus salmonis (Krøyer) has been reported to cause increased cortisol levels, alterations in physiological homeostasis, osmotic imbalance and mortality in salmonids (Grimnes & Jakobsen 1996;Bjorn et al 2001;Heuch et al 2005;Sivertsgard et al 2007) and salmon farms are assumed to be among the main causes of mortality in juvenile wild salmonids, constituting a contributing factor to decreasing stocks of wild fish (Bjorn et al 2001;Krkosek et al 2007;Costello 2009). The high concentration of potential hosts for lice in sea pens has been a problem since the onset of the salmon farming industry in the 1970s.…”

“…Furthermore, such medical treatments are often expensive (Costello 2009), stressful to fish (Burka et al 1997) and hazardous to the environment (Burridge et al 2010). …”

Relationship of farm salmon, sea lice, and wild salmon populations

“…B ecause salmon aquaculture production has rapidly increased over the past three decades, the potential for environmental impacts of salmon farms has generated heightened scientific and public interest (1,2). One concern about salmon farms is that they are the source of ectoparasitic sea lice infestations that might reduce the marine survival of wild salmon (3,4).…”