Do farmed salmon transfer sea lice to wild salmon?
Sea lice are a naturally occurring parasite that can affect both farmed and wild salmon. Pacific salmon species have lived with consistent background levels of sea lice for centuries, and have developed a natural tolerance to this parasite. Because of this, farmed Atlantic salmon are somewhat more susceptible to sea lice in the Pacific and farmers raising Atlantic salmon must be even more diligent in their monitoring of and response to sea lice on their farms. Sea lice can be transferred in both directions between farmed and wild salmon. Their levels are controlled on farms through proper siting, raising only a singe age-class of salmon on a farm to break the life cycle of the sea lice, and through the strictly-controlled use of medication if an outbreak does occur. In general, farm fish carry lower levels of sea lice than wild adult salmon, due to the ability to control lice levels on the farm.
