Photo: Sea lice: An old problem that won't go away

(Credit: Watershed Watch via Flickr)

By John Werring, senior science and policy adviser

Some things — like sea lice — just won't go away. Sea lice are a naturally occurring parasite of ocean fish and need hosts to survive. A sea louse's preferred host is an adult salmon, and the more fish there are in the water the greater the number of lice. Since wild salmon migrate, sea lice numbers in waters near the shore are typically low when the salmon are at sea and spike when the salmon return in the fall. When juvenile salmon migrate out of their home streams in the spring and enter the salt water, sea lice numbers are usually low (because they have no hosts to feed on during the winter), so encounters between fish and lice are fairly rare. There have been very few documented events where natural sea lice numbers are so high that they actually become a problem for wild fish.

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Fish farms have altered this natural balance. Millions of farmed salmon are held captive in pens for up to two years, providing sea lice with a year-round supply of hosts and allowing the lice to breed in enormous numbers, including when wild salmon are absent. When sea lice reproduce, their microscopic offspring are carried away from farms on ocean currents, leaving more in the surrounding environment. Thus, when juvenile fish exit their home rivers in spring and enter the sea in areas where there are fish farms, they can encounter far higher numbers of lice than evolution has prepared them for. This has led to entire stocks of wild salmon lost to sea lice.

The David Suzuki Foundation, along with the Coastal Alliance for Aquaculture Reform, has worked during the past decade with government and the aquaculture industry to come up with strategies to protect wild B.C. salmon from parasitic sea lice. We convinced them that reducing farms along major salmon migration routes was an effective strategy; we convinced them to monitor and publicly report weekly sea lice numbers on farms during the salmon out-migration period; and we convinced them to treat farms with high sea lice infestations well in advance of the wild salmon migration.

We could monitor how farms were doing ourselves because the data were timely and publicly available. This has changed. New research by Alexandra Morton suggests that this year's wild salmon in the Broughton Archipelago are heavily infested with sea lice. This means one of two things: either effective sea lice management strategies are not being followed, or they are and the chemicals used to treat fish for sea lice, such as SLICE, or emamectin benzoate, are not as effective as they once were. Maybe the lice have developed resistance to the chemical treatments.

To know for sure requires data from the Department of Fisheries and Oceans Canada. Since it took over management of the aquaculture industry (fish farms) in 2010, DFO has collected quarterly data on the prevalence of sea lice on farmed salmon as well as information about the amount of chemicals being used to treat for lice. By the time DFO reviews, formats and translates this data into publically available reports they are hopelessly out of date, sometimes by as much as nine months. In practice, that means up-to-date data about the source of a serious environmental problem are not available.

Meanwhile, DFO scientists have determined that "environmental conditions have been ideal this past season for high challenge levels of sea lice in the Broughton: the warm, dry winter may have contributed to faster sea lice development ... compared with a normal year." (From personal email correspondence from Fisheries and Oceans Canada.)

They argue this is why wild fish are showing lice infestations, yet they won't let us see farmed fish data even though farmed fish are hosts for sea lice too.

There's something fishy going on and wild salmon are the big losers.

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May 20, 2015
http://www.davidsuzuki.org/blogs/healthy-oceans-blog/2015/05/sea-lice-an-old-problem-that-wont-go-away/

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