Sea Lice Parasites
A study reported in the journal Science in December 2007 documents just how much of a threat
is posed to wild salmon by the sea lice that amplify in salmon farms.[1]
Sea lice are parasites, which naturally occur in the wild.
They latch onto and feed off salmon. Normally, they attach themselves to adult
fish, usually in numbers too low to cause harm to adult wild salmon. When adult
salmon enter fresh water rivers to spawn, sea lice die off because they can
only survive in salt water. This ensures that under natural conditions there
are no sea lice when emerging juvenile salmon (smolts) head out to the open
ocean in the spring.[2],[3]
The problem is that sea lice numbers amplify in the heavily populated factory-farm conditions found on salmon farms, where there can be up to a million fish on one site.[4],[5] When an infestation breaks out, it can transform farms, some of which are located at the mouths of important spawning rivers, into a year-round source of sea lice.
The juvenile pink and chum salmon do not have the protection of scales when they emerge from the rivers. These fragile juvenile migrating wild salmon swim near the farms or directly through the open net-cages, where they can take on a sea lice infestation that they are too small to survive.
The effects of sea lice infestation on some annual runs of wild salmon have been devastating. Up to 2001, there was no problem with sea lice on juvenile salmon in B.C. With the advent of Atlantic salmon open net-cage farms there was a 98% crash in pink salmon returns in the Broughton Archipelago in 2001 with a subsequent 97% collapse in 2002.[6]
Interestingly, Alaska does not have in-shore salmon farms and does not report sea lice on juvenile salmon.[7],[8]
A 2009 review of sea lice science has confirmed that open net-cage farms are the most significant source of sea lice on juvenile wild salmon and that "the most likely cause of the global decline in wild salmonids in areas with farms was sea lice transmission from farms".[9]
Recent studies have further proven that the effects of sea lice are passed up the food chain. One study (Biology Letters, 2008) proved that in approximately 70% of trials, the sea lice on juvenile pink and chum salmon escaped predation by moving onto the predator (coho smolts or cut-throat trout).[10] Two studies in the October 2010 Journal of Applied Ecology proved that coho salmon are impacted as sea lice are passed up the food chain. One study indicated that sea lice transmitted from pink salmon prey to coho predators increased infection on coho by 2 to 3 fold in salmon farming areas[11]. The second paper found that infected coho in the Broughton Archipelago suffered a 7-fold decrease in productivity during a period of recurrent sea louse infestations associated with salmon farms.[12]
Yet a further study (PLoS One, February 8, 2011) provides the first link between salmon farms and elevated levels of sea lice on juvenile Fraser River sockeye salmon.[13]
[5] Review "Sea lice and salmon in Pacific Canada: ecology and policy" Martin Krokosek; Frontiers in Ecology and the Environment 2009
[7] 1989 State of Alaska ban on finfish farming offshore. Click for Source 7.
[8] Ban applies to State waters from 0-3 miles offshore. Click for Source 8.
