A closer look at Sea Lice on 15 Salmon Farms

There has been a lot of talk about sea lice infestation of fish farms lately. According to a recent article from the North Island Gazette, there were more than the ‘acceptable’ number of parasites on fourteen sites this Spring. The President of Cermaq Canada just sent an industry perspective of this issue to the Strathcona Regional District Board. I decided to take a closer look at the sea lice on 15 salmon farms.


I used the 2019 industry sea lice count database that Stan Proboszcz, fisheries biologist with the Watershed Watch Salmon Society, quotes in the North Island Gazette.

However, lacking his scientific background, I decided to look at five fish farms (each) from Cermaq Canada, Grieg Seafood BC and MOWI Canada West (formerly Marine Harvest Canada).

Seven of these sites were selected from the list in the North Island Gazette. There is an (L) following their names in the charts below. The remaining sites were chosen from two groups: farms that appear to be strongly challenged by sea lice and those that are not. My decision to look at 9 farms from one group and 6 from the other is arbitrary.

A true representation would be more diverse and not so evenly divided among the three companies.

Looking at healthy looking salmon swimming by the net in cage #5, Phillips Arm – courtesy Marine Harvest Canada (2016).

Sea Lice

Amy Jonsson, Communications and Engagement Manager with Cermaq Canada, explained, “Sea lice occur naturally in the marine environment and their abundance is influenced by seasonal and year-to-year variations in ocean salinity, temperature and other environmental conditions. DFO’s Conditions of Licence for aquaculture require strict ongoing inspection of farmed fish to monitor sea lice levels and implementation of management measures so that sea lice numbers are at their lowest during the outmigration of wild juvenile salmon, from March 1 to June 30 of each year.”

Screenshot from Alexandra Morton’s YouTube video Hard Evidence shows abnormally thin fish looking out through the net.

The Accepted Number Of Sea Lice

Fisheries and Oceans Canada set the permissible limit at 3 lice per fish between March 1 and June 30, when wild salmon migrate out to sea.

“This limit was set by DFO science based on risk assessment and potential risk to wild salmon,” wrote Jonsson.

According to the Living Oceans Society report Lousy Choices II ,

“In three of four regions studied by independent scientists this year, wild
juvenile salmon have been found infected with lice at levels certain to result in death. Infestation rates exceeded 90 percent of the sampled outmigrating fish and the intensity of infestation—averaging up to 9 lice per fish—is probably lethal to all wild salmon.”

“In the fourth region independently studied this year, the Broughton Archipelago, lice levels were remarkably low on wild juveniles (season average 1.3 lice per fish; infestation rate 34%), with some samples completely clear of lice. This is the first outmigration to follow on the closure of 6 of the Broughton’s salmon farms, in accordance with the historic Broughton Agreement that places the farms under co-management with First Nations. The Nations’ first priority was to open up an ‘exit corridor’ for outmigrating salmon.”

Limit Remedial Time to 10 Days

Proboszcz told the North Island Gazette, “There’s no impetus for the industry to change if there’s no fines or repercussions. DFO says they can take a licence away at anytime, but have there been any examples of fines? I haven’t heard of any.”

Farms that exceed the accepted number of lice are currently given 42 days to clean up their act. 

One of the recommendations in the Lousy Choices II report is that the remedial time be limited to ten days. 

David Kiemele, Managing Director of Cermaq Canada, wrote the SRD that his company is already implementing this.

He added, “As part of our new Conditions of License (March 1st 2020), there is an increased monitoring and management requirement in February to ensure that farms are below the threshold going into the outmigration period.” 

Do Chemical Baths & the Hydrolicer Work?

Lousy Choices states: “Nearly 70 percent of bath and mechanical treatments failed to control sea lice for more than 4 weeks; and many of those treatments failed to reduce lice levels at all.” 

Kiemele disagrees with this analysis:

“The Lousy Choices II report indicates that the Hydrolicer has a low efficacy rate on the basis that farms may require an additional treatment four weeks later. Treating our farms multiple times is factually correct. In some circumstances, we have treated our farms for a second time within weeks, and the reason is not connected to the efficacy of the treatment.” 

“ … The frequency of use of a tool like the Hydrolicer is entirely dependent on the abundance of sea lice in the ecosystem; meaning the higher the number of sea lice in the ecosystem, the more frequently we will need to treat our farms. Sea lice numbers can fluctuate depending on several factors such as water temperature, salinity and the in migration of wild salmon. Once lice enter our farms, as with any farmed animal, the parasites can undergo an amplification effect. Because of these dynamics, we monitor lice levels on a weekly basis and plan to treat the farms when lice levels are seen to be increasing.”

So what does the data I collected suggest? 

Data from Greig Seafood Salmon Farms

High & Low monthly counts from five Greig Seafood Salmon Farms in 2020, using data published by Fisheries and Oceans. Farms appearing in the list of 14 have an (L) beside their name. – Roy L Hales

I examined data from three of the Greig Seafood farms in Nootka Sound that are in Proboszcz’s list of 14 problematic sites (Altrevida, Gore and Williamson).

On February 7, the infestation rate at Atrevida was only only 0.55. This number climbed to 1,63 when a second test was made, on February 27th. After that the numbers took off. They were 6.30 on March 6th. Treatment failed, and the number climbed to 7.10 by March 17th. By the end of the month, the count was 9.38 lice per fish. The treatments appear to have been successful after that, but needed to be repeated on a monthly basis.

A month after a highly successful cleansing, the lice count at Gore was 5.14 on February 13th. Two cleansing operations appear to have failed and by March 7th the count peaked at 9.78. The next treatment brought the number down to 4.39 and by March 18th it reached the far more acceptable 0.89. This cycle of high counts followed by treatments was repeated the following two months.

After four treatments, the sea lice problem at Williamson was finally brought under control by February 1st. The number was rising by the end of the month, but still an ‘acceptable’ 1.65. Then, on March 21st, the count was 3.58. After two more treatments, a test taken on April 16 found only 0.53. However, this pattern was repeated in May.

As previously mentioned, these sites were chosen because of their lice problems.

While the data follows the pattern described in Lousy Choices, it does not tell us where the lice originated. Environmentalists are concerned about farms infecting migrating salmon, but previous industry studies have shown that migrating salmon can also infect the pens. Assuming this is correct, are sea lice being introduced to the pens throughout the migration period?

Is the infection spreading both ways?

I also selected two farms in the Esperanza Inlet (Esperanza and Hecate) because of their low lice counts in January. While Esperanza approached the threshold in May, I have seen no data showing either site exceeding it.

Data From MOWI Salmon Farms

sea lice at five MOWI salmon farms
High & Low monthly counts from five MOWI West Salmon Farms in 2020, using data published by Fisheries and Oceans- Roy L Hales

The three MOWI farms that I chose from the list of 14 (Shaw Point, Cougar & Mahatta East) also appear to conform to the pattern of multiple treatments suggested by Lousy Choices II. 

I specifically chose Koskimo because of its low lice count in January. This changed in March, when the numbers climbed from 1.65 to 4.67 per fish. Remedial action was taken and the figures from April are much better. This is the only site chosen for its low January count that later crossed the threshold.

The only salmon farm I have actually visited was the Marine Harvest Canada facility in Phillips Arm, during October 2016. Walking into the control room, I saw the surveillance screen that you see further up the page. Alexandra Morton had just released the video Hard Evidence.” Marine Harvest allowed me to direct their cameras, so that I could look for the aberrantly thin salmon and ‘sickly’ fish behaviour Morton described. I did not find anything like it. Nor, looking the lice count above, does Phillips Arms have much of a problem with sea lice.

Data From Five Cermaq Salmon Farms

sea lice at five Cermaq salmon farms
High & Low monthly counts from five Cermaq Salmon Farms in 2020, using data published by Fisheries and Oceans – Roy L Hales

The five Cermaq Canada sites I chose are all in Clayoquot Sound.

“We acknowledge we had two challenging years in 2018 and 2019 in Clayoquot Sound, and in response, we have dedicated significant capacity and resources towards lowering sea lice levels at our farms. We have been successful in achieving that goal,” writes Kiemele.

While the data from Millar Channel conforms to the pattern described by Lousy Choices, the counts from Bawden & Ross Pass clearly do not. I selected these farms because of their high counts on January 3rd, 2020. The ratio was 4.19  & 3.90 lice per fish respectively. Both sites were treated and subsequently found to be in compliance. Instead of the four weeks suggested by Lousy Choices, three months passed before these farms needed to be treated again.

On April 6 Ross Pass was found to be approaching the threshold (2.88) and on April 8th Bawden exceeded it (3.85). Both sites were treated and subsequently found compliant. 

Statistics from the two Cermaq sites I chose because of their low lice counts in January (Dixon Bay & McIntyre Lake) remained low throughout the period being studied.

Scenario One: An Industry Survey

According to an industry financed survey of fish farms conducted by Mainstream Biological Consulting in March, April and May 2020:

  • Juvenile Chum in Clayoquot Sound region: – 6% had three or more lice; 5% had two lice and 89% had one or no lice.
  • Juvenile Chum & Pink Salmon in the Discovery Islands: – 2% with three or more lice; 3% with two lice; 95% one or no lice.
  • Salmon in the Broughton Island Region: – “A total of 904 individual samples underwent lab analysis for sea lice infestation … 206 individuals were infested with 307 sea lice.”

This suggests that only a relatively small number of salmon are infested with lice to the degree depicted in photo below.

sea lice levels
Sea lice on a juvenile salmon. “What’s an analogy … it’s like a beaver-sized parasite just chewing on me, and putting holes in my body,” Proboszcz said. – Tavish Campbell photo used by the North Island News.

Scenario Two: Lousy Choices II

A much different picture is presented by the Lousy Choices II report, which is based on surveys of migrating wild salmon:

” … 38 percent of farms operating during the 2020 spring outmigration
failed to keep lice levels under the treatment trigger of 3 lice per fish (based on data to the end of April, representing half of the outmigration period.) … We noted 11 instances where SLICE™ was used successfully after bath and/or mechanical treatment had failed to reduce lice loads below the management threshold. As resistance to the drug becomes more commonplace, this technique will fail more often. Had it failed in these 11 cases, we would have seen 64 percent of farms exceeding the management threshold. This augers poorly for the future of lice control under existing regulatory measures.”

Comparing The Data

Assuming that all the data is correct, only three of the fifteen farms I looked (Atrevida, Gore and Shaw Point) reached the infestation level (9 lice per salmon) that Lousy Choices reports was common in wild salmon by the time they reached the Discovery Islands.

Though most of the farms I looked at were chosen because they were infested, only eight exceeded the accepted number (3 lice per fish) during March. This number dropped to seven, but includes a farm whose count appears to normally be much lower, in April.

This suggests that there were probably more lice on wild salmon and they probably were infecting the pens.

However the lice count at seven of the sites I looked at – Atrevida, Bawden, Cougar, Gore, Ross Pass Shaw Point and Williamson – was already over the limit in January.

So, the Spring migration was not the sole source of this problem.

In fact, the infestation may have been spreading both ways.

Lousy Choices points to a noticeable drop in the Broughton Archipelago’s infestation levels after six salmon farms were removed.

What Does It All Mean?

The Lousy report adds:

… Although there is, unaccountably, no clear evidence to indicate
what levels of infestation sockeye can survive, even the DFO’s aquaculture scientists agree that sockeye experience a significantly elevated stress response and alterations in blood chemistry indicative of dehydration when exposed to lice in a laboratory setting. In the wild, infestation has been demonstrated to reduce their ability to compete for food, which likely governs their chances for survival.

Eight Recommendations

The authors of the Lousy Choices Report made eight recommendations on how to improve the industry:

Cermaq Responds

According to David Kiemele, Cermaq Canada “is already implementing six of these eight recommendations to [a] varying extent.”

“The remaining two recommendations – Recommendation 2: DFO should set limits on the total abundance of lice per farm and area; and Recommendation 4: Lower the sea lice treatment threshold to at least 0.5 female lice per fish – are complex due to the interpretation of risk and regional and seasonal variables, and both conversations being held within several industry, stakeholder, Rightsholders, and government working groups in which Cermaq is participating.”

Top photo credit: Seafarm from the Surface – courtesy Marine Harvest Canada (2016).