Sea louse

A sea louse (plural sea lice) is a name given to any oceanic stinging larvae, which includes many juvenile cnidarians (notably "Linuche unguiculata"), and isopods. [http://news.nationalgeographic.com/news/2001/05/0530_sealice_2.html] [http://www.eol.org/taxa/17063791] On humans, contact with the skin can seem similar to a dull jellyfish sting and cause a rash, sometimes referred to as swimmer's itch. In several islands of the southern Caribbean, including St Lucia, Grenada, and St Vincent and the Grenadines, sea lice are also known as 'sea ants' and are reputed to sting bathers who urinate in sea water.

almon and sea lice

There is reported concern that sea lice flourishing on salmon farms can spread to nearby wild juvenile salmon and devastate these populations. [ Martin Krkosek, Jennifer S. Ford, Alexandra Morton, Subhash Lele, Ransom A. Myers, and Mark A. Lewis (14 December 2007), [http://www.sciencemag.org/cgi/content/summary/318/5857/1711 Declining Wild Salmon Populations in Relation to Parasites from Farm Salmon] . "Science" 318 (5857), 1772.] Sea trout populations in recent years have seriously declined due to infestation by sea lice from salmon farms. [cite book |author=Clover, Charles |year=2004 |title=The End of the Line: How Overfishing is Changing the World and What We Eat |publisher=Ebury Press |location=London |isbn= 0-09-189780-7] However, there is still very little known about the larger ecological interactions and it is too early to pinpoint, conclusively, that aquaculture is a major source of lice that infect wild salmon.

As sea lice develop from eggs to adults, they shed their exoskeletons in a series of moults. This creates a number of identifiable life stages. Sea lice in the first two stages are called nauplii. Nauplii can neither feed nor attach themselves to fish. In the next, copepodid, stage, the lice can attach themselves to fish. They then moult through four chalimus stages during which they are anchored to a host fish. As pre-adults (two stages) and adults (one, final stage), they can crawl about the host fish. It appears that they are most damaging to the host fish in these final, motile stages.

Sea lice have always been relatively common on adult salmon as they return to spawn. However, sea lice cannot tolerate fresh water, and drop off the fish as they encounter reduced salinities. Natural infection dynamics on wild salmon are not well understood. However, lice are typically very rare on juvenile salmon in areas far from fish farms.

Smaller host fish appear to be particularly vulnerable. Hence, pink salmon ("Oncorhynchus gorbuscha"), which migrate out to sea immediately upon emergence from spawning gravel, are particularly at risk. Nonetheless, larger species, specifically including wild Atlantic salmon ("Salmo salar") have been found to have lethal lice loads near fish farms. Sea lice are also economically damaging to the fish farms themselves; in one recent year, sea lice cost salmon farmers more than US$100 million for treatment and lost production, which represents about 20% of their total costs.

Currently, fish farmers rely heavily on the chemical emamectin benzoate (SLICE) for controlling sea louse infestation rates. Many governments now impose limits on sea louse infestation levels on fish farms. The adequacy of existing regulations, and the environmental impacts of the use of SLICE are highly controversial. Public opinion is particularly polarized in the northeast Pacific where a moratorium on expansion has been lifted by the British Columbia government while the Alaska government is maintaining a total ban on salmon farming in its waters.

References

*cite web |url=http://www.watershed-watch.org/sealice.html |title= Watershed Watch an organization that promotes salmon conservation in British Columbia. Watch their descriptive video on Sea Lice and Salmon
*cite news |url=http://www.sfu.ca/mediapr/news_releases/archives/news03060601.htm |title=Study provides first direct evidence sea lice kill young wild salmon |publisher=Simon Fraser University |year=2006
*cite web |url=http://www.sfu.ca/cstudies/science/sealice.htm |title=Wild salmon and sea lice |publisher=Simon Fraser University