Fish populations are plummeting and, for once, it’s not a result of overfishing. In an important new paper in Nature, researchers show that parasitic sea lice from fish farms are causing wild salmon populations to collapse. The problem is so severe that there could be a 99 percent decline in certain wild salmon populations over the next four years, the scientists report.
Sea lice are parasites that attach themselves to salmon, feeding on their skin and tissues. Salmon farms, with their density of fish, are fertile breeding grounds for these lice. The farms, as it turns out, are also often located along the migration routes that juvenile salmon take to the ocean. As the young salmon migrate past these farms, they often pick up the parasites. Though adult fish can survive these infestations, research has shown that wild juveniles not only contract, but also die from, sea lice from these fish farms.
But until now, it wasn’t clear how seriously this transmission was affecting wild populations. In this new paper, researchers at the University of Alberta studied wild salmon populations in an archipelago about 260 miles northwest of Vancouver. Young salmon there have to swim through nearly five miles of fish farms on their way to the sea. They found a steep population decline over the past four years—more than 80 percent of the salmon that annually return to the archipelago, they calculated, died as a result of the sea lice. What’s more, they report, the sea lice have been even more devastating to the area’s wild salmon population than commercial fisheries were. The findings cast serious doubt on the safety of many kinds of fish aquaculture. Let’s just hope it doesn’t give commercial fisheries an excuse to ramp up their business.
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