Fish farm removal had little impact on sea lice numbers: study

Photo: DFO

Overall, sea lice on farmed and wild fish prevalence has not changed much over the past five years.

There has been little change in average sea lice levels in juvenile wild salmon in the Discovery Islands, following the removal of open-net salmon farms, despite claims of a 95% decrease, according to a new report by the BC Salmon Farmers Association.

The report by Brian Kingzett, the association’s science and policy director, used sea lice monitoring data collected by independent biological consulting firm Mainstream Biological Consulting.

It is worth noting that the claim of a 95% decline in sea lice in wild salmon after some fish farms were removed is also based on Mainstream data.

Kingzett's report concludes there has been virtually no change in the level of sea lice on wild salmon in the area of the Discovery Islands, where some open net salmon farms were ordered removed by the minister of Fisheries and Oceans in 2020, over concerns that open-net fish farms posed a potential disease transmission threat to migrating wild salmon.

“Since 2017, out-migrating juvenile wild salmon have been monitored annually by independent professional biological consultants in multiple salmon farming regions of British Columbia,” Kingzett says in his report.

“During this time there has been no trends showing an increase in sea lice levels in wild salmon that have migrated past salmon farms in the Discovery Islands region. Sampling has continued in 2021 and this trend has not changed with the departure of salmon farms from the Discovery Islands.”

The claim that there has been a 95% decline in sea lice on wild salmon in the area after fish farms were removed in 2020 is based on data from a single sub-region where salmon farms have been removed: Okisollo Channel and Owen Bay.

“This claim has been taken up by multiple media and social media sources and used as a justification that the ministerial decision was correct,” Kingzett says in his report. “This claim is simply not true.

“Sea Lice levels on juvenile salmon in the Discovery Islands are low and did not change after decreased production in the area,” Kingzett writes.

Alexandra Morton – an independent researcher who has led the campaign against open-net salmon farms in in B.C. – said the 95% decline is based on the industry’s own reporting. It is drawn from data for chum and pink salmon in the Okisollo Channel and Owen Bay, where salmon farms have been removed.

She points out Mainstream’s own reporting showed a prevalence of sea lice of 71.4% and 78.6% in chum salmon in Okisollo and Owen Bay, respectively, and 63.2% and 70.6% prevalence rates for pink salmon. These numbers are based on small samples of chum and pink.

“In 2021, they don’t offer prevalence, but if you do the math their data reports only 6.45%, 10% of chum were infected in Okisollo/Owen Bay,” Morton explained in an email.

She said "the BC Salmon Farmers Association headline that lice levels are 'unchanged' is not supported by the data they have."

More broadly, there does appear to have been little change in sea lice prevalence in wild salmon over the last five years in both the Discovery Islands and Broughton Archipelago.

Salmon farms can amplify sea lice infestations, but sea lice infestations can also occur naturally. A natural abundance of wild salmon, for example, could result in higher levels of sea lice, regardless of whether fish farms are present or not. In other words, there are natural causes that also need to be factored in.

The Department of Fisheries and Oceans appears to have no data of its own on sea lice on wild salmon in the region. It appears to confine its monitoring of sea lice to fish farms only.

“Fisheries and Oceans Canada (DFO) staff regularly conduct site inspections at farms, which include sea lice counts on farmed fish,” DFO said in a statement to BIV News. “The average number of sea lice on farmed fish has remained fairly stable over the last 5 years, including since December 2020.”

That also appears to be the trend in the Broughton Archipelago, according to a 2021 report by the Salmon Coast Field Station (SCFS) – which Morton co-founded.

“Sea louse numbers on juvenile salmon in 2021 were comparable to levels over the last five years, and higher than the period 2008-2014,” an SCFS 2021 report concludes. “Of the pink and chum examined, 58% had at least one louse, and louse counts averaged 1.16 lice per fish.”

That average intensity of about 1.16 lice per fish in the Broughton Archipelago generally matches what the Mainstream data found in the Discovery Islands.

The data collected since 2017 by Mainstream found average sea lice counts of 1 to 1.21 per fish in pink salmon, and a prevalence rate ranging from 1.8% to 13.7%, between 2017 and 2020.

In 2021, there was 1.14 lice per fish and prevalence rate of 8.8%.That is in post-exposure areas – i.e. after wild fish would have been exposed to salmon farms.

So looking at that specific dataset, there was indeed an overall decrease in the prevalence of sea lice and average number per fish between 2020 and 2021, but it was nowhere near 95%.

It’s important to note that, though some open-net salmon farms in the Discovery Islands have been removed, not all have been.

So until the entire region is clear of fish farms, it is a bit premature for any conclusions to be drawn by either side, said Andrew Bateman, salmon health manager for the Pacific Salmon Foundation.

“I would say it’s premature to draw firm conclusions,” he said. “From PSF’s perspective, the BC Salmon Farmers report from yesterday presents some good raw data information, but it’s not analyzed in a way that allows us to draw conclusions.

“We have no reason to doubt the actual data behind the report,” Bateman said. “I’d say it’s more the way the data have been presented and summarized that, I would argue, paints somewhat of a biased picture. It’s an industry report, and it’s presenting an industry perspective.

“What you find, when you dig into their more detailed annual reports, is that they actually found the same pattern for that same sub-region in the Okisollo Channel,” Bateman said. “Between 2020 and 2021, their counts of sea lice declined drastically on fish that they caught in that Okisollo Channel.”

What is needed is ongoing monitoring of wild salmon in the Discovery Islands after all open-net salmon farms are out of the area before any definitive conclusions can be drawn.

“There are different perspectives in this whole debate, and different sides can cherry pick information to make different points,” Bateman said. “I think it’s important that we step back and, once all the data are in, and as the data come in, that we try to take a more detached perspective and assess things little bit more rigorously.”

“A careful, impartial assessment of those data after a number of years would be an excellent course of action.”