A panel of scientists that was often at odds has told the Cohen Commission that sea lice can't be fingered as the cause of the decline of sockeye salmon stocks, but the parasite may be a contributing factor.
Simon Jones, a research scientist with the Department of Fisheries and Oceans, and Sonja Saksida, executive director of the Centre for Aquatic Health Sciences, told the federal commission that they don't think sea lice are having a major, direct impact on sockeye populations, or that salmon farms are the cause of lice infestations in wild stocks.
But Craig Orr, executive director of the Watershed Watch Salmon Society, and Mike Price, a biologist with the Raincoast Conservation Foundation, said that sea lice are likely doing significant damage and that fish farms are a big source of infestations.
All four witnesses replied in the negative when asked if sea lice "acting in isolation" could have caused the collapse of sockeye salmon stocks.
"No … but nor do I believe sea lice do act in isolation," said Mr. Price, expressing the view that lice are part of a complex and still emerging picture.
While all four were sworn in as expert witnesses on the subject of sea lice, their diverging views on the topic underscored one of the main difficulties Mr. Justice Bruce Cohen of the B.C. Supreme Court is facing in his inquiry. Science is not certain on many of the topics that have come under scrutiny, because so little is known about what happens to salmon in their early life stages.
"There is this big black hole … you don't know what happens to fish when they leave freshwater," said Dr. Saksida, who suggested water temperatures, salinity and the abundance of food may be more important factors than sea lice.
Dr. Jones told the commission the science on sea lice in the Pacific is still relatively new, and that's why the picture remains so murky. He said studies in Europe and on Canada's East Coast are of limited help, because the sea lice found in the Pacific are genetically different from those in the Atlantic.
"The science of sea lice in British Columbia is still in its infancy," he said, noting that studies of B.C. sea lice date back only to 2002. "There is still an awful lot we have to learn."
But Mr. Price and Dr. Orr said studies they have been involved with make it clear that wild salmon are being infested with sea lice that originate in salmon farms.
Mr. Price said by looking at young salmon before and after they swam past salmon farms, they were able to confirm that lice infestations intensified in wild salmon stocks, after they encountered farms.
Dr. Jones, however, said there may be other explanations. He suggested, for example, that the increase in lice might be attributed to the fact the young salmon had been at sea longer by the time they got past the salmon farms, which are concentrated near the north end of Georgia Strait.
Dr. Jones added that research he's done has shown that tiny fish, known as the stickleback, carry large numbers of lice, and that could be a source of infestations in wild salmon. He also said his laboratory tests show that pink salmon – which are thought to have been devastated by lice infestations around farm sites in the Broughton Archipelago – aren't that vulnerable to lice.
However, that prompted Dr. Orr to question the "real world" value of Dr. Jones's study, saying that, in nature, pink salmon would be exposed to sea lice two to three times longer than those in the lab tests.
Dr. Orr also said it is almost impossible to determine the indirect toll of sea lice, because infected fish swim differently, attracting predators and getting eaten, rather than being killed by parasites.