Pacific salmon may be more resistant to sea lice
than their Atlantic counterparts and more research is needed to
determine if sea lice found in fish farms are impacting wild
salmon, says a new study, released today by The Fraser Institute.
"Large gaps remain in our understanding of the impact of sea lice
on Pacific salmon and whether or not fish farms contribute to the
problem," said Dr. Kevin Butterworth, co-author of
Sea Lice: The Science Behind the Hype
, and a Research Associate at the Centre for Aquaculture and
Environmental Research at the University of British Columbia.
"Through our research, we've found that Pacific salmon appear to
be less susceptible and more resilient to sea lice than Atlantic
salmon. Much of the information available on the impact of sea
lice is from Atlantic salmon, not Pacific salmon."
The study, co-written with Dr. K. Fiona Cubitt, Dr. Bengt
Finstad, and Dr. R. Scott McKinley, points out that in B.C.
waters, 14 different species of sea lice exist, but only two
species pose a potential threat to wild and farmed salmon.
Butterworth said the difficulties in distinguishing between sea
lice species can contribute significantly to the public
perception of the impact of sea lice on both wild and farmed
salmon. If these species are not correctly identified, the
inferences that fishermen and the general public make about the
origin of the sea lice on juvenile Pacific salmon can be
The study shows that wild salmon vastly outnumber farmed salmon
in BC, with 128 salmon farm tenures in BC, compared to more than
9,600 distinct stocks of wild Pacific salmon. Additionally,
over-wintering wild coho and chinook salmon and schools of wild
sticklebacks in coastal waters provide ideal, potential hosts
upon which the sea lice can over-winter, ready to infect
out-migrating wild smolts in the spring. As a result, there is
potentially a larger reservoir of sea lice associated with wild
fish than with farmed salmon. This is the opposite of the North
Atlantic, where due to the severe depletion of wild fish stocks,
it is primarily the salmon farms that contain the largest pool of
potential hosts upon which sea lice can over-winter.
Additionally, Butterworth and the other researchers determined
that sea lice are native and prevalent in the North Pacific Ocean
and are found on 90 per cent of salmon.
"There is no doubt that sea lice transfer from wild salmon to
farmed salmon. There are no sea lice on farmed salmon when they
are transferred from freshwater hatcheries to the sea farms to be
grown through to market size."
But he points out that many questions remain about the movement
of sea lice from farmed salmon in net-pens to wild Pacific
salmon. The study suggests more research is needed to answer two
1. Is the number of sea lice transferred from farmed salmon to
wild Pacific stocks large enough to have an impact on the
infestation level in the wild stocks?
2. What is the minimum number of sea lice on individual Pacific
salmon species at which point the health of the salmon is
"It remains important that sea lice are monitored on farmed and
wild salmon until the relationship is better understood. But
until these questions are answered, we can not conclude that sea
lice found in salmon farms are significantly impacting wild
Pacific salmon," Butterworth said.