Lousy Sea Lice, potential impacts on wild and farmed salmon.


Image by Bill Keay of the Vancouver Sun

Sea lice on a juvenile Pink salmon.

Salmon lovers may be dreading the already observable, or soon to increase prices of salmon, thanks to parasitic sea lice plaguing Norwegian and Scottish fish farms. Such news should not only concern Canadian consumers, but a strike fear with those involved within Canada’s $670 million (as of 2015) salmon farming industry. Why? Well these same sea lice (also known as sea louse) can harm farmed and wild salmon within our shores.

What exactly are sea lice?

There are two species of sea lice (C. clemensi & L. salmonis) largely responsible for impacting Canadian salmon farming. These small parasites generally don’t impact large adult fish, relying on the parasitic interaction to leach life from salmon, but not kill them. But in smaller juvenile fish sea lice have a more significant impact, and are more susceptible to mortality cause by sea lice.

Wild Salmon and Aquaculture

Prevalence of sea lice (Catligus clemensi) on sockeye salmon increases with proximity to salmon farms, and even further downstream of salmon farm (Price et al. 2011)

The potential impact salmon farms may have on sea lice, and the consequent impact on wild salmon has been heavily scrutinized. This topic has received enough attention to garner it’s own research area by the Canadian DFO.   As of recent, numerous studies have begun to illustrate that salmon farms do impact wild salmon, as increased sea lice parasitism has been observed on chum, pink & sockeye (right) populations in proximity to salmon farms.

Why does this occur?

Salmon farms densely pack a large number of salmon within a confined area, in which higher density facilitates increased sea lice density in the water. These salmon farms with high densities of sea lice are situated along migratory pathways of juvenile salmon, in which expose juvenile salmon to sea lice that normally wouldn’t be present at the time of migration.

Managing Sea Lice

So not only do the sea lice directly affect the salmon in the farms, but may also harm wild salmon. As such the industry has researched several strategies to mitigate sea lice populations.


Land or closed system aquaculture pens

  • Prevent any interactive affects between farms and wild salmon>
  • Increased cost to farm

Introducing natural predators

Novel mechanisms to remove sea lice


Sea lice and salmon farm interactions have been heavily debated, and will likely continue to be. I believe that salmon aquaculture does in fact impact wild salmon, but such affects may have been masked by the effectiveness of pesticide treatments. With recent findings, to promote conservation and sustainability of salmon aquaculture requires continued research and application to minimize the sea lice impact on both farmed and wild salmon.

Image References


Price MHH, Proboszcz SL, Routledge RD, Gottesfeld AS, Orr C, Reynolds JD (2011) Sea Louse Infection of Juvenile Sockeye Salmon in Relation to Marine Salmon Farms on Canada’s West Coast. PLoS ONE 6(2): e16851. doi:10.1371/journal.pone.0016851