The farmers were using underwater noisemakers to ward off predators, but the sound kept the whales from their feeding grounds as well. A Canadian government study found harbor porpoises also avoid the noise and there is some evidence herring, wild salmon and other fish may be impacted. A year ago the salmon farms near Morton's home and research station agreed to turn off the noisemakers and since then some of the whales returned, she said. The B.C. fisheries lab in Nanaimo, on Vancouver Island, may have a better solution to predators. Scientists there began tossing dead fish to a seal when she came to visit.
Few farms are likely to adopt predators though.
The predator nets are effective unless a strong current pushes the outer net against the inner net, allowing sea lions to snatch bites of the trapped fish. New pen designs may be even more effective. Some hold the net taut so it cannot be moved by currents. Others screen off the pen so predators won't see the fish. The public toilet Better nets might reduce the number of escaping salmon, but even penned salmon hurt the habitat, say environmental groups.