Clayoquot Sound, B.C. Sea Lice Study Update
Audrey Thompson, Biologist, Wild Fish Conservancy
Wild salmon declines across the Northwest are blamed on many things including harvest, competition with hatchery salmon, degraded freshwater habitat, pollution, and disease, not to mention natural pressures. Salmon life history is complex and teasing apart the bottlenecks in salmon survival is difficult. With so many factors at play it is difficult to identify specific problems, and therefore difficult to create effective management solutions.
There are exceptions to the rule, however, and Clayoquot Sound, Vancouver Island, is one of them. As in so many other places, the native salmon runs of Clayoquot have dwindled to a fraction of their historical levels. Clayoquot has some pristine old-growth ecosystems that are relatively untouched by humans. Even though these freshwater habitats are not degraded, salmon here are still in crisis -- something is broken. The science staff at Wild Fish Conservancy saw a unique opportunity to study salmon that have started their life cycle with a clean slate in a wild river, and began searching for answers.
The first human influence Clayoquot salmon fry encounter is aquaculture facilities along their migration corridors. Scientific literature has documented that these facilities are correlated with an unnatural abundance of salmon lice. Salmon lice are a natural part of the environment and are relatively harmless to adult salmon, but can have impacts on vulnerable juveniles that can lead to decreased fitness and possible mortality. WFC researchers wanted to know if sea lice are a problem for out-migrating chinook and chum salmon in Clayoquot Sound where aquaculture facilities are a prominent feature of the landscape, and began research in the spring of 2009 to answer that question.
In 2009 and 2010, WFC biologists found chum fry in fjords with salmon farms had higher lice infection rates than fry in fjords with few or no farms. Fry caught closer to the ocean and later in the season had the highest infection rates, though the timing and intensity of the infestation was slightly between years. This trend can be attributed in part to seasonal warming of the ocean and more time spent in saltwater. What cannot be attributed to environmental variables is the fact that the magnitude of the infection was different in different fjords, where temperature and salinity were similar. Fjords with the most farms had the highest lice infection rates, while fjords with few or no farms had very low infection rates. A late and cold spring in 2009 resulted in an approximately four-week overlap between peak lice production and peak smolt migration to the sea. In 2010, with warmer spring water temperatures, the lice bloom began earlier and overlapped for a longer duration with smolt outmigration meaning higher infection rates, and faster lice maturation before smolts left the fjords than in 2009.
Overall, it seems like sea lice may be part of what’s broken for salmon in Clayoquot Sound, but the story is still incomplete and there are many other factors to consider. Clayoquot Sound has some of British Columbia’s best remaining habitat for salmon, and if there is any place where there is still hope for recovery of salmon runs, this is it.