Experts find a way to track onslaught of sea lice

DNA research at the University of Guelph has provided insight into a perplexing environmental problem on British Columbia's west coast, where fish farms have been blamed for lice epidemics that have devastated wild salmon stocks.

Researchers have long known that fish farms are incubators for lice and that wild salmon stocks in the vicinity of farms, particularly in the Broughton Archipelago off northeast Vancouver Island, have suffered from devastating lice infestations.

But because lice are almost invisible at the larval stage, it has been impossible for researchers to track the parasites as they drift with ocean currents from host to host.

That has left the route of transference to be largely a matter of guesswork.

Now a team led by Elizabeth Boulding, a professor in the Department of Integrative Biology at the University of Guelph, has used DNA barcoding techniques to trace the path of transmission of lice to and from wild fish.

DNA barcodes are short genetic markers that - much like barcodes on supermarket items - allow researchers to quickly identify differences between species, or population differences within a species.

In an interview, Dr. Boulding said the research, while preliminary, shows it is now possible to map out both where and when lice move from farms to passing wild salmon.

"The reason this is important is that we can now ... tell how far away [farm] lice have to be, before there is no longer a danger of their larva being transmitted to the wild salmon," she said.

Environmentalists concerned about a collapse of pink salmon in the Broughton Archipelago have been arguing that salmon farms should be moved away from the migration routes of wild salmon.

Dr. Boulding said her research confirmed that the lice on the farmed and wild salmon in the archipelago were the same, but lice were different in another coastal region. The research also showed that after leaving the farmed fish and affixing to wild salmon, some changes took place that showed up in the DNA barcode marker.

Being able to find such distinctions within lice populations means it should now be possible to tie specific farms to lice on wild salmon and to determine where and when the transfer occurred.

"If you took lice off the juvenile pink salmon that were swimming by a farm and you found the gene sequences in the juvenile wild salmon were the same as those currently on the farm, that would be kind of a smoking gun," she said.

Her study relied on widely selected samples, collected in different years, and did not attempt to link specific farms to lice on wild salmon.

Dr. Boulding said more research is needed, but it's clear from the data gathered so far that fish farms and young baby salmon aren't a good mix.

"At the moment it seems what we have to do is remove the net pens in space and time from the baby wild salmon swimming out from the freshwater, into the estuary and past the salmon pens," Dr. Boulding said.

The research paper by Dr. Boulding's team appears in the current issue of the journal Aquatic Research.