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Warming temperatures in 2015 caused more lice infestations in young salmon, study says

While many young people experience head lice, young salmon are experiencing a similar, but more severe, problem: sea lice.

Salmon lice, Lepeophtheirus salmonis, are common parasites found on adult wild and farmed salmon, but a recent study has found that lice have been creeping onto juvenile salmon in BC in 2015, likely due to warmer temperatures. The study, published in the August issue of the Canadian Journal of Fisheries and Aquatic Sciences, found that lice levels last year were the highest observed since 2005. It predicted that the lice outbreak will cause a 9 to 39 per cent mortality rate in young salmon from 2015.

According to quantitative ecologist Andrew Bateman, University of Alberta postgraduate and one author of the study, lice generally affect adult salmon that live away from spawning grounds, so wild juvenile salmon rarely encounter the parasite. But juvenile fish swimming out to sea from rivers pick up lice as they pass the salmon farms, which have high salmon population densities that are optimal conditions for lice reproduction.

Bateman said lice can wound young salmon by feeding on their skin, mucous, and blood. Lice can also cause wounded fish to swim at the rear of their schools, where they are easier for predators to catch.

“If you were to imagine the effects of sea lice on salmon in (a human context), it would be similar to having a leech the size of your head stuck to your body,” Bateman said.

In order to manage lice on farmed salmon, Bateman said farms in British Columbia place a chemical called SLICE in fish feed. The SLICE chemical was performing fairly well in handling the sea louse levels, but Bateman said warmer temperatures in 2015 likely caused lice to reproduce much earlier in the season than usual. And because the SLICE chemical was administered at around the same time as it had been in previous years, it was less effective overall.

Bateman said better communication techniques could be implemented between scientists and farmers to help allow fisheries tailor chemical usage specifically towards the lice problem. And because some farmers count the number of lice per fish to assess the need for sea lice management chemicals, Bateman suggested that farmers count the number of lice per region, as those numbers take both wild and farmed salmon into account.

In the long term, Bateman said moving the farms onto land would reduce the spread of lice between wild and farmed salmon.

“From a consumer perspective, it’s important for people to know more about what they eat,” he said. “From an ecological perspective … wild salmon have a large impact on the terrestrial and oceanic ecosystem.”

One Comment

  1. Ever heard of balance in Journalism? This reads like an advertisement and is clearly advocacy dressed as science. Apparently the quantitative ecologist from Alberta knows very little about the complex life cycle of the sea louse. To speak of relationships amongst sea louse/ farmed salmon/ and wild salmon and not mention the known, well documented, and significant source of wild/endemic/natural sea lice in British Columbia is not only irresponsible but deliberately misleading.

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