Wild salmonids are running the gauntlet of pathogens and climate as fish farms expand northwards says a new report published by the ICES
The ICES Journal of Marine Science has published a paper called “Wild salmonids are running the gauntlet of pathogens and climate as fish farms expand northwards”
The report claims that salmon farming has dramatically altered the disease dynamics between farmed and wild salmonids. Pathogens are allowed to freely spread through the water due to the open net-pen production, but even though the effects of these pathogens on wildlife are largely unknown, it is generally recognised as a key threat to sustainability.
In the report the authors claim that the conflict surrounding salmon aquaculture is often simplified into the discussion of the effect of sea lice from farmed fish on out-migrating wild salmon smolts, which has led to numerous studies on the impact of this parasitic copepod on marine survival of wild salmon. They say there is now little debate about whether salmon lice can have a negative impact on wild salmon, but it is still highly controversial how much of the declining marine survival of salmon observed in some regions can be attributed to the salmon lice originated from fish farming.
The study claims to have found that in Norway, lower densities of sea lice in the north can be attributable to less intensive fish farming and colder annual temperatures that prolong generation time of the parasite and therefore a lower infestation pressure. This has set the fish farming in Norway on a path to greatly expanding its production in northern regions, setting a course for rapid changes in disease dynamics.
On pathogens the report says that aquaculture facilities can act like a reservoir with potential “spillback” to wild populations leading to the view that the high-density net-pen culture of farmed fish in areas inhabited by wild fish is a pressing issue.
Studies on pathogen dynamics of salmonid populations are emerging and revealing the complex role that these species have in the life cycle of salmon, trout, and charr. Much of the focus has been placed on ectoparasitic sea lice, but molecular techniques and epidemiological studies have begun to reveal the role of a broader number of infectious agents.
The report concludes by saying “ Shifting political will to increase the production of fish farms in northern regions raises questions about what the future might hold for wild salmonid populations as the climate in these regions change more rapidly than that in other parts of the world. We emphasize the importance of considering uncertainties with respect to pathogen dynamics when considering new directives for aquaculture in poorly studied regions of the north until the key research questions are fully addressed and appropriate plans have been implemented to minimize the potential for harm to vulnerable wild salmonid populations.
To read the full report click here.