Recent work by Martin Krkosek of the University of Alberta has demonstrated strong links between the practice of salmon aquaculture and the incidence of sea lice infestations that threaten wild populations. One study used mathematically coupled datasets on the transmission of sea lice (Lepeophtheirus salmonis) on migratory pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. They concluded that:
Farm-origin lice induced 9–95% mortality in several sympatric wild juvenile pink and chum salmon populations. The epizootics arise through a mechanism that is new to our understanding of emerging infectious diseases: fish farms undermine a functional role of host migration in protecting juvenile hosts from parasites associated with adult hosts. Although the migratory life cycles of Pacific salmon naturally separate adults from juveniles, fish farms provide L. salmonis novel access to juvenile hosts, in this case raising infection rates for at least the first 2.5 months of the salmon’s marine life (80 km of the migration route).
Packing fish together in pens that are open to the sea is an almost ideal mechanism for breeding and distributing parasites and disease. In nature, you would never find salmon packed 25,000 to an acre. Keeping them in such conditions - and making them grow as quickly as possible - generally requires chemical manipulation. The earlier discussion here about antibiotic use and its role in the emergence of resistant bacteria is relevant.
These concerns also exist in addition to the fundamental reason for which fish farming cannot be sustainable: it relies on catching smaller and less tasty fish to feed to the tastier carnivorous fish that people enjoy. It thus lets us strip the sea bare of salmon or cod or trout and compensate for some period of time by using cheaper fish as a factor for their intensive production. Given that those cheaper fish are caught unsustainably, however, fish farming simply delays the emergence of truly empty oceans. And the industry is trying to have farmed salmon labelled ‘organic.’ Ludicrous.
Source: Krkosek, Martin et al. “Epizootics of wild fish induced by farm fish.” Proceedings of the National Association of Sciences. October 17, 2006, vol. 103, no. 42, 15506-15510.
P.S. Shifting Baselines also has some commentary on sea lice and salmon farming.
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“If nothing changes we are going to lose these fish,” Mr. Krkosek said of the wild pink salmon stocks in the Broughton. “The population growth rate for the pink salmon in the Broughton during the infestations has been significantly negative. … extinction probability is 100 per cent and the only question is how long that’s going to take.”
He estimated the stocks will be locally extinct within four years.
“It’s the first time that we’ve had enough detailed data to actually measure the effect of sea lice on wild salmon populations,” said Mr. Krkosek, who looked at DFO records dating from 1970 for 71 salmon rivers.
“What we found is that before the sea-lice infestations began in the Broughton, the pink-salmon populations there were just fine. They had positive population growth rates. … But when the sea-lice infestations began, and they have been recurrent since then, we measured a sharp decline in the population growth rate.”
Mr. Krkosek said wild-salmon populations in an area just north of the Broughton, where there are no salmon farms near spawning rivers, have continued to thrive.
To play devil’s advocate for a moment:
If we can get all the salmon we need from farms, what is the importance of the wild populations?
Here is a typical journey for a Norwegian salmon destined for sale in a supermarket in America or Europe
Nature 451, 23-24 (3 January 2008) | doi:10.1038/451023a; Published online 2 January 2008
Aquaculture: The price of lice
Andrew A. Rosenberg
Wild salmon stocks in Canadian coastal waters are being severely affected by parasites from fish farms. So intense are these infestations that some populations of salmon are at risk of extinction.
during a fishing trip the other week in north wales,uk I found myself lucky enough to catch a salmon. My first thought was “is it not a bit late in the year to be catching salmon and brought on concerns of prehaps global warming affecting the way fish behave. expecially as we have just had our second bloom this year which is a verry unusal affair, I have been told this is another cause of global warming. Upon further inspection of the salmon it did have these “tic like creatures” on one side which i now know are sea lice. it was a fairly large sized salmon at 5 and a half pouns but looked fit and healthy. i know these lice only really affect the baby salmon but what percentage of wild salmon are dying due to reasons of these lice. and should we not be more concerned about other matters such as global warming and overfishing.