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Killer lice Add to ...

Ye ugly, creepan, blastit

wonner,/ Detested, shunn'd,

by saunt an' sinner,/

How daur ye set your fit upon her,/ Sae fine a Lady!

- From the Robert Burns poem, To A Louse, On Seeing One On A Lady's Bonnet,

At Church

For anybody who relishes the unctuous feel of lox on bagel, the crunch of crispy salmon skin in a B.C. roll, or the odour of a Chinook tail on the barbecue, these can be confusing times.

Wild salmon are virtually extinct in the Atlantic Ocean, yet tens of millions of Atlantic salmon are being raised in farms in the Pacific; the U.S.-based Safeway supermarket chain has announced that it is curtailing purchases of disease-ridden farmed salmon from Chile; and returns of wild salmon on the British Columbia coast seem to be declining from year to year.

Choosing farmed salmon, some people will tell you, means consuming some of the most toxic chemicals known to humanity. Opting for wild-caught salmon, others insist, could make you complicit in driving already fragile salmon stocks to local extinction. No wonder so many people end up settling for chopped cucumber in their maki rolls at the sushi bar.

Yet there really is no need for confusion. Where you stand on the wild-or-farmed-salmon issue should come down to what you think about a thumbtack-sized crustacean that survives by eating the scales and skin off the same fish that we love to eat - an ugly, creeping, little beastie known as the sea louse.

I was first shown sea lice on salmon smolts by Alexandra Morton, an American-born marine biologist who has lived in a floathouse in Echo Bay, in the Broughton Archipelago, for more than 20 years. The Broughton, a jumbled jigsaw puzzle of islands scattered off B.C.'s mid-coast, is home to sea otters, great blue herons and, until recently, a resident population of killer whales. It is considered one of the richest pockets of biodiversity on the coast - or at least it was until the salmon farms came along.

Aboard her boat one afternoon, Ms. Morton told me how she had welcomed the first net cages when they were towed into local bays in the late 1980s: She hoped that they would provide employment for local people. But then the killer whales were driven away by the acoustic devices the farms used to discourage them and other predators, fishermen started pulling up prawn traps and clams dripping with rotting pellets and salmon feces, and the wild salmon began to disappear.

In the late 1990s, a Scottish tourist at a fishing lodge near Ms. Morton's floathouse asked, "Do you have the scourge of the sea lice yet?" The visitor explained that after the salmon-farming industry came to Scotland, sea lice started appearing in great quantities on wild fish; he had seen the same parasites on the salmon he had just caught in the Broughton.

Alarmed, Ms. Morton took out a dip net and pulled up dozens of wild juvenile pink salmon. They were bleeding from the eyeballs and the base of the fins. Most of them were covered with brown flecks - juvenile sea lice. As they grow, changing their body shape every few days, these parasitic copepods strip mucus, scales and skin from the growing fish. While a full-grown salmon has an armour coating of scales and can survive an infestation, the parasites exhaust the young fish and quickly kill them off.

Using hand seine nets to sample local waters, Ms. Morton established that the salmon farmers were raising millions of adult farmed Atlantic salmon along the migration routes of wild Pacific salmon - in exactly those inlets and estuaries where juvenile wild Pacific fattened up before going to sea. Suddenly, the decline of wild salmon populations did not seem like such a mystery: The 27 farms in the Broughton, had, by crowding normally nomadic fish into tightly packed nets, become ranches for sea lice, concentrating and fatally passing on parasites to wild salmon when they were at their most vulnerable.

In 2002, government scientists predicted that 3.6 million pink salmon would return to the Broughton. Fewer than 150,000 did - a 97-per cent-population crash.

Though the salmon farming industry has done its best to muddy the waters, Ms. Morton has science, as well as some of the leading fisheries scientists in the world, on her side. Analyzing data from Ireland, Scotland and Atlantic Canada, the late Ransom Myers of Dalhousie University showed that disease and parasites spread by farmed salmon reduced the survival of local populations of wild salmon and sea trout by more than 50 per cent per generation. In December, 2007, Ms. Morton and colleagues from the University of Alberta and Dalhousie published a paper in Science, one of the world's most prestigious peer-reviewed science journals, projecting the complete collapse of pink salmon in the Broughton by 2011 if the sea lice continue to infest fish.

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