Sea Lice AND Salmon - Farmed And Dangerous

Sea Lice &Salmon Farming1. WHY ARE SEA LICE OFTEN MENTIONEDIN DISCUSSIONS OF SALMON FARMING?Although sea lice occur naturally in the NorthernHemisphere, lice infestations have onlyrecently put wild salmon populations at risk.The stocking of thousands of fish in smallareas makes fish farms ideal breeding groundsfor lice, and drastically increases the number oflice in surrounding waters. Understandably, licefind it easy to parasitize farmed fish because oftheir high densities. Additionally, the stress levelsassociated with crowding make farmedsalmon more susceptible to lice infestation. [50,51] Nor should we forget that 80% of BC’sfarmed salmon are of the Atlantic variety, [10]which are inherently more susceptible to sealice than many other salmon species. [57, 58]Fish farms are typically located in shelteredbays and inlets near rivers on or near themigratory routes juvenile salmon use to reachthe ocean. In the pre salmon-farming era, sealice numbers were typically low in the springbecause the number of available hosts incoastal areas was also low. That salmon farmscreate an unnatural reservoir of sea lice isespecially serious for juvenile wild pink andchum salmon heading for the ocean simplybecause of their small size and because of thestresses associated withchanges that occur when theyenter saltwater. One or twosea lice may be enough to killa juvenile pink salmon newlyarrived in saltwater. Muchhigher numbers have beenobserved recently on juvenilepink salmon near BC’s salmonfarms.2. DO SEA LICE MOVE FROMFARMED TO WILD FISH?There is much debate about whether sea lice onnet-penned farmed salmon can infect wildsalmon in their natural environment. For 10years, industry and government have insistedthat the sea lice in salmon farms do not constitutea risk to wild salmon. Meanwhile, significantfindings—including a growing body of circumstantialevidence from studies throughoutthe Northern Hemisphere—suggest the opposite:that sea lice are dangerous to wild salmon.Common sense suggests that sea lice cantransfer from farmed to wild salmon. Farmedsalmon juveniles are raised in large, landbasedfreshwater tanks. Because sea lice cannotsurvive in fresh water for more than twoor three weeks at most, [60, 70] juvenile farmedsalmon host no sea lice when they are transferredto marine net pens.The sea lice’s free-swimming stage, and theopen nature of salmon farm net pens, makefarm smolts vulnerable to infestation fromolder farmed salmon [61] and/or nearby wildsalmon. Sea lice outbreaks can occur becausethe breeding conditions for sea lice are idealon a salmon farm. Untreated, sea lice outbreakscan result in large numbers of freeswimminglarvae in and around the salmonfarm. The distance these larvae travel from thefarm depends largely on ocean currents.Adjacent tosalmon farms,where thousandsof fish arecontained insmall areas, sealice populationscan becomevery large.One or two sea lice may be enoughto kill a juvenile pink salmon.Alexandra Morton photoSea Lice and Salmon: Elevating the Dialogue11