Sea Lice and Juvenile Salmon: Fatal Combination

December 2003 - January 2004

This is an article from WaveLength Magazine, available in print in North America and globally on the web.
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by Alexandra Morton

2.1 gram pink salmon that died with one louse.

As the planet’s most intelligent species, we have been slow to learn that breaking natural laws comes at a terrible price. Over the past three years, I have studied the sea lice epidemics that have emerged in the waters around my home in the Broughton Archipelago, located off the northeast coast of Vancouver Island. Concurrent with these epidemics has been the greatest collapses of pink salmon numbers in recorded history.

Is there correlation between the proliferation of salmon farms, sea lice epidemics and the collapse of wild salmon stocks? I believe so, as do a number of international respected scientists, some employed by the federal Department of Fisheries and Oceans (DFO).

Our politicians can no longer risk the optics of ignoring this little pest. Absolutely everywhere net-cage salmon farming is practiced, lice outbreaks occur. The management of this parasite has become critical to conserving the last wild salmon stocks in Canada, Scotland, Norway and Ireland.

Sea lice are not ugly or nasty. For a parasite they are positively chaste, turning out astonishingly few offspring. Scientists marvel that they exist at all. To the lice, each fish is a planet unto itself, safe haven from the abyss. Youngsters are forced to disperse. They must sink or swim in the dog-eat-dog world of the plankton layer before growing what it takes to latch onto a fish.

L. salmonis, the louse, gambled and has become a specialist. As its name implies, it can only attach to salmon. On an adult salmon its touch is light, as it does not want to kill its planet. But for tiny pink and chum smolts first voyaging to sea, even one louse can be fatal.

In Norway, scientists are encouraged to study sea lice on salmon farms for the express purpose of protecting wild salmon, because where salmon farms operate in their long narrow fjords, wild salmon decline by 98%. The cause is considered to be lice. They found that young Atlantic salmonids can survive with about one louse for each gram of their weight. These salmon species spend a year or more in rivers so when they enter the sea they are large enough to bear about 10 lice. Norway mandates stiff measures on salmon farms to try to keep lice on nearby wild salmon below that number.

In BC, however, this limit on lice cannot work, as pink and chum salmon are much smaller than any other salmon when they go to sea. Pinks and chum are newly hatched when they leave their natal rivers, and in the Broughton Archipelago weigh about 0.3 of a gram when they reach the fish farms. This means they are likely much too small to survive even a single louse.

Sea lice are a natural phenomenon, but they die when carriedupriver by spawning salmon. As a result the coast is clear of lice when the baby fish appear in the spring. But tying a salmon farm to shore is like building a heated subdivision in the tundra. Now instead of dying off, the lice over-winter, multiplying relentlessly on the merry-go-round of confined fish, releasing billions of larvae to feed on the tiny pinks and chums in spring. The biological principle sustaining both louse and fish has been shattered, resulting in plague and pestilence. When will we ever learn?

The fish farmers’ attempt to reduce lice with the pesticide SLICE solves nothing, while generating a bigger problem. When a pink salmon dies of fewer lice, it is just as dead, and we can expect SLICE to indiscriminately kill the essential food species young salmon depend on, as well as our shrimp and prawns—in fact, all crustaceans.

Surely, destroying wild salmon is not a requirement to farm salmon. The solution is uncomplicated; salmon farms and very young wild salmon must never meet. Currently salmon farms are located deep in the best wild salmon nursery grounds of BC, and this is not working. The farm salmon are dying of viruses and the wild salmon are dying covered in lice. Because salmon farms can be moved and better contained, and our wild salmon cannot, the answer is clear: move the farms and better contain them. Our political leaders and DFO will have to be pressured to take this step, because from here in the Broughton, it is painfully clear that wild salmon will not survive unless we, the people who value them, ensure this happens.

© Alexandra Morton, R.P.Bio, has been observing, recording and reporting on salmon farming since 1987 when the first farms came to her area.