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]

A recent study has further proven that the effects of sea lice are passed up the food chain.[10] In this study, 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).

[1] http://www.sciencemag.org/cgi/content/abstract/sci;318/5857/1772

[2] http://www.worldwildlife.org/what/globalmarkets/aquaculture/WWFBinaryitem11790.pdf  

[3] http://www.georgiastrait.org/files/share/PDF/08_11FraserSeaLiceScienceUpdate-12.pdf  

[4] http://www.livingoceans.org/files/Maps_PDF/FF_sealice_on_juvenile_salmon_june2008.pdf  

[5] Review "Sea lice and salmon in Pacific Canada: ecology and policy" Martin Krokosek; Frontiers in Ecology and the Environment 2009  

[6] http://www.sciencemag.org/cgi/content/abstract/sci;318/5857/1772

[7] 1989 State of Alaska ban on finfish farming offshore http://www.commerce.state.ak.us/oed/seafood/seafoodfaqs.htm  

[8] Ban applies to State waters from 0-3 miles offshore http://findarticles.com/p/articles/mi_hb5261/is_12_21/ai_n29227587/  

[9]  http://rspb.royalsocietypublishing.org/content/early/2009/07/02/rspb.2009.0771.long

[10] http://www.sosfoundation.ca/files/Sea_lice_escape_predation_on_their_host.pdf