Sea lice are decimating Atlantic salmon, and climate change is making the situation worse

A Dalhousie University researcher is among a team of scientists tracking a big threat to Atlantic salmon: sea lice.

Climate change can increase risks of disease in marine ecosystems and pose an additional threat to the health of Atlantic salmon, according to a recent paper published in Nature’s peer-reviewed journal, Scientific Reports, and authored by scientists from Canada, Finland, and Norway.[1]

The experimental work undertaken in a Dalhousie University lab shows that as climate change warms ocean waters, the negative effects that sea lice have on their salmon hosts will worsen. Sea lice are an external parasite that attach to and feed off salmon.

“Our waters are getting warmer along coastal Nova Scotia,” says Dalhousie University biology professor Jeffrey Hutchings, one of the paper’s authors. “They’ve been getting warmer for a while and they will continue to get warmer. So we were looking at this interaction of increasing water temperature and the degree to which this might exacerbate the negative influence of sea lice on salmon growth and survival. And we found that it exacerbated it quite a bit.”

Hutchings calls climate change the “elephant in the room” and something that “we are not accounting for” in any of our coastal industries, including how warming ocean waters will affect Atlantic salmon.

And anything that affects sea lice infestations has major implications for open-net pen salmon farming.

Hutchings and his co-authors note that open-net pen salmon farming is the most lucrative form of aquaculture globally, but that in the past two decades, sea lice have challenged “the economic and ecological sustainability of the industry.”

This has led the federal government to push for a phase-out of open-pen salmon farms in the Discovery Islands on Canada’s West Coast, but not on the East Coast.

Odd, that, especially because sea lice are as much of a concern in Atlantic Canada as they are in British Columbia, and possibly even more.

Two coasts, double standards

“Sea lice counts in parts of the Bay of Fundy – where open-net pen site density is highest in Atlantic Canada – can exceed numbers produced in British Columbia, where they have had devastating impacts on wild salmon populations,” says Simon Ryder-Burbidge, marine conservation campaigner at the Ecology Action Centre. He points to the 2020 sea lice management report for New Brunswick of the Atlantic Canada Fish Farmers Association, in which sea lice counts for certain regions showed upwards of 40 lice per fish twice between January and April.

“Those numbers are insane,” Ryder-Burbidge tells the Examiner. “For reference, two to six sea lice can kill a wild salmon smolt, depending on the size of the fish.” A smolt is a young salmon that is ready to migrate to the sea.

Ryder-Burbidge notes that the risk assessment for sea lice on salmon in Norway uses a mortality rate based on lice-per-gram of a salmon smolt, which corresponds to 0% mortality if there are fewer than two lice per fish, 20% if there are two to four lice, 50% if there are four to five lice, and 100% if there are more than six lice for a 20-gram salmon smolt.

Sean Godwin is an ecologist and a postdoctoral fellow at Dalhousie University, and lead author of the recent study on the effects of water temperature on sea lice. In an interview from British Columbia, where he continues to research sea lice and salmon farming, including into resistance of sea lice to the chemicals used to treat them in open-net pen salmon farms on the Pacific Coast, Godwin said that the numbers of sea lice reported in Bay of Fundy fish farms are “absolutely wild” compared with what happens out West.

He points out that the Atlantic Canada Fish Farmers Association’s 2020 sea lice report shows only the counts for adult female lice, whereas there are four stages of “motile” (capable of motion) sea lice — pre-adult male and female, and adult male and female — that are counted on the West Coast. Godwin says that to compare the Atlantic Canada sea lice numbers to those on the West Coast, it would mean multiplying the 40 female lice per fish by at least two.

Such numbers of lice would not be tolerated in Pacific Canada or in Europe, Godwin says. “If we had something that gets up to like six or seven [lice per fish] for a sustained period of time, it’s a huge deal, newsworthy out here. Six or seven motile lice would be like three adult female lice. And that report shows you have farms hitting 40 female lice.”

In British Columbia, just three motile lice per fish is the threshold that triggers costly but mandated delousing treatments.

Godwin says that in British Columbia, raw data on sea lice is all public and transparent, whereas in Atlantic Canada there is very little data transparency, because industry and the federal Department of Fisheries and Oceans (DFO) are not required to publicly report their sea lice counts as they are on the West Coast.

But that seems to be no deterrent to the industry.

Big plans for more open-net fish farms in Nova Scotia

Cooke Aquaculture has plans to massively expand its salmon farming off Nova Scotia, and has applied for two new sea sites and the expansion of an existing site in Liverpool Bay. (Linda Pannozzo has reported extensively for the Examiner on current and proposed open-pen salmon farms in Nova Scotia here, here, here, here, and here.)

There has been a proliferation of groups opposed to open-net pen salmon farming in ocean waters off Nova Scotia and to government support for it, and several of them have joined forces as the Healthy Bays Network, which calls itself “Nova Scotia’s public voice in opposition to the open net-pen salmon industry, advocating for healthy bays full of wild marine life and free of pollution.”[2]

Among the many concerns about open-net pen salmon farming are the pollution it causes and its negative effects on marine ecosystems and other aquatic species including lobsters, the amount of wild fish needed to feed the farmed salmon, and the diseases and genetic risks they pose to wild salmon health and populations. [3]

Now, it looks as if there is yet another concern that needs to be factored in: climate change.

Warmer water, more sea lice, more health problems

Godwin and his co-authors of the recent study write that the sea lice outbreaks increase in frequency and severity, and also develop more rapidly in warmer water, which may further reduce the survival of the fish hosts. (The Examiner also contacted Cooke Aquaculture to ask its reaction to these findings, but has had no reply.)

Godwin is also lead author on a paper that made waves last year and garnered considerable media attention because of its findings that from 2011 to 2016, salmon farming companies on the West Coast had been under-reporting the number of lice on their fish.

Speaking about his more recent paper during a Dalhousie University biology department seminar, he noted:

We found that the consequences of sea louse infestation for juvenile Atlantic salmon do seem to be mediated by temperature; the results are pretty clear. And as temperature increased, so too did the effects of sea lice on the growth rate, the body condition [how “plump a fish is], and the survival.

Godwin also said that a complementary experiment led by Kate E Medcalf at Dalhousie found still more ways that higher temperatures and sea-louse infestations harmed salmon, impairing their internal organs.

He tells the Examiner that the experiment in the Dalhousie lab had to be done with hatchery fish, as the scientists “obviously couldn’t have caught a thousand wild Atlantic salmon and done this experiment on them.”

Says Godwin:

One of the reasons I’m still on the West Coast is that I can actually study these questions here. You can’t really study the effects of salmon farms on wild salmon out there [on the East Coast] because there are so few wild salmon. I can’t go out and catch wild salmon in the ocean, and see how many sea lice are on them. Those populations are so small that you just can’t do that. It’s always been that way. Pacific salmon have always been more abundant than Atlantic salmon, but also [wild] Atlantic salmon are in dire straits in Atlantic Canada.

However, Godwin doesn’t think that the use of hatchery fish affects the results.

He says the laboratory study at Dalhousie University has implications for both farmed and wild Atlantic salmon populations around Nova Scotia and more broadly:

We know that sea lice outbreaks on salmon farms harm wild salmon, and they can harm wild salmon populations. And we also know from our paper that the effects of sea lice on salmon survival and growth and body condition will get worse at higher temperatures, so as sea lice transfer between wild and farm populations, we expect that the effects of these sea lice will get worse as our oceans warm.

Godwin tells the Examiner that the transmission can go both ways and it can happen over long distances:

So it’s not just farm to wild, sea lice will also move from wild to farmed [salmon]. The way it works is they just grow to adulthood, and then they have these [sea lice] egg strings, that the eggs get released into the ocean and then they hatch as larvae, and then the larvae attach to wild fish. It’s not like the fish just had to swim past the [salmon] farm right next to it. It is more like a larval plume, like a cloud, that extends like 30 kilometers from the farm.

None of this bodes well for already severely diminished wild Atlantic salmon populations.

They’ve already been decimated by a barrage of threats that have arisen since the arrival of Europeans and their destructive ways on these shores.

A short history of Atlantic salmon seems appropriate here.

Salmon stocks are “depleting”

A 2016 paper that provides “Mi’kmaw perspective on advancing salmon governance” by Shelley Denny and Lucia Fanning of Dalhousie University, states that salmon — or plamu — are “one of many animals that contributed to Mi’kmaq sustainability.” The authors write:

Historically, salmon were a staple food that was dependable, predictable, and could be found in most rivers in Nova Scotia. As one of the last fish harvests of the season before travelling inland to escape winter, the women would preserve the salmon through smoking over an open fire using heated rocks (A. Marshall, personal communication, November 15, 2014). Today, because of a lack of abundance and concern for local populations, it is often reserved (though not exclusively) for special occasions such as pow-wows or other large gatherings where the serving of a large fish such as salmon is preferred.[4]

As Kwilmu’kw Maw-Klusuaqn (KMK) – the Mi’kmaq Rights Initiative – points out, the Mi’kmaq of Nova Scotia “have a Right to harvest Salmon under the Food, Social and Ceremonial (FSC) fishery,” while also noting that “salmon stocks are depleting.”

KMK continues:

It is important now, more than ever, that the Mi’kmaq help create, report and collect accurate data, based in Mi’kmaw science. Conservation is a responsibility of us all; together, the Mi’kmaw Nation needs to ensure that salmon will be available for seven generations to come.

June 1st, 2015 the Assembly [of Nova Scotia Mi’kmaw Chiefs] rolled out the Mi’kmaq Plamu/Salmon Management Plan for Nova Scotia, in cooperation with KMK, the Unama’ki Institute of Natural Resources (UINR), and Mi’kmaq Conservation Group (MCG). This Plan was created to balance the Right to Salmon harvesting for the Mi’kmaq of Nova Scotia, while respecting the conservation.

A litany of threats

A 2011 paper called “Canada’s Species at Risk Act and Atlantic salmon: Cascade of promises, trickles of protection, seas of challenges,” on which Hutchings was one of three authors, says this about the diminished state of wild Atlantic salmon populations 10 years ago:

Although Atlantic salmon was once an important commercial and recreational fishery, a spiritual component of traditional Aboriginal family and community, and a centrepiece for thriving ecosystems, today salmon populations are severely depressed and extirpated [locally extinct] from many river systems in Europe and North America. By 1970, the species’ production capacity had been reduced to 32 per cent of its estimated original productivity. Since 1970, salmon abundance has declined dramatically, and today stands at the lowest level known in history. According to a 2001 assessment, salmon have become extinct in 84 per cent of American rivers, and are critically endangered in the remaining 16 per cent.[5] (emphasis added)

The situation for Atlantic salmon in Canada may be “less bleak” but it’s still grim. Says the same paper:

While Canada’s prospects seem less bleak with several rivers containing healthy salmon populations, particularly in the northern range of the Canadian distribution, most Canadian salmon populations appear to be in various stages of decline. From 15 conservation units of anadromous [fish that migrate up rivers to spawn] Atlantic salmon reviewed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in Eastern Canada, five have been assessed as endangered; one threatened; four are of special concern; four are not at risk; and one population is considered to be data deficient.

In other words, populations of wild Atlantic salmon populations are in deep trouble.

Some of the problem stems from the damage that humans have wrought on the freshwater rivers in Atlantic Canada, where the fish spawn and spend the early years of their lives before they head off into ocean waters and begin making regular migrations to and from destinations as far away as Greenland.

That is particularly true for stocks from the southern range of salmon in eastern Canada, which includes Nova Scotia. Jeffrey Hutchings tells the Halifax Examiner that salmon populations here “are doing much worse than the more northerly populations of Atlantic salmon in eastern Canada.”

Hutchings acknowledges the factors that affect salmon in freshwater, such as:

… dams, which can affect migration up river and down river, and issues associated with land-use practices and the degree to which land use increases the siltation of rivers, which can be a problem for fish that are trying to breathe clean, clear water, as well as habitat alterations.

Acid rain has also taken a severe toll on the rivers along Nova Scotia’s Atlantic Coast — and on the wild Atlantic salmon populations that depend on them along the “Southern Uplands,” as the Examiner reported here.

Hutchings says that in some parts of Nova Scotia, “acid precipitation remains one of the key factors affecting the survival of especially young Atlantic salmon.”

But there are also problems at sea, says Hutchings, where wild salmon have been experiencing higher mortality.

Open-pen salmon farming a major “stresser”

There is another major “stresser” to wild Atlantic salmon populations, says Hutchings:

That’s the [open-net pen] fishing farming side of things that has been identified by COSEWIC [Committee on the Status of Endangered Wildlife in Canada] and by DFO recovery strategies for salmon, as one of the threats to wild salmon populations from a couple of perspectives.

Hutchings continues:

One has to do with the escape of farmed fish from the net pens because of all kinds of different reasons. And many of those fish end up swimming into the rivers and interbreeding with wild salmon. And we know that the offspring of this interbreeding do not survive as well as do the offspring of pure wild salmon. So when you have this interbreeding of farmed fish with wild fish, it dilutes the genetic strength of those wild salmon populations. That’s an issue because the salmon populations are very small.

And then there’s a related issue has to do with disease transfer, and that’s related to the observation that fish farms, because of the extremely high density of salmon that are in the cages, are basically major sources of sea lice, a pathogen that occurs naturally in the environment, but that occurs at unnaturally high densities in net pen areas.

And climate change, as their recent study shows, is likely to further increase the negative impacts of sea lice infestation.

“Like a nightclub in COVID”

Godwin hesitates when asked what he thinks the solution is to sea lice, and when he does reply, he chooses his words carefully:

From a scientific point of view and using the precautionary principle, with only science in mind, one might say you would want to get salmon farms out the water. There are other things at play here, like economic and social considerations in addition to that.

He says that when salmon are farmed in land-based closed containment systems, rather than in open pens in the ocean, sea lice are no serious problem because the effluent can be treated.

“The issue with open-net salmon farming is that there’s no barrier at all between the farm environment and the external environment, just the net,” says Godwin. “The water and any pathogen or parasite can move freely past that.”

During the Dalhousie University biology seminar in March, Godwin noted:

One of the major sources of concern for marine disease is aquaculture, the farming of marine organisms. Aquaculture operations typically raise a lot of organisms in a really small space. So like a nightclub in COVID, aquaculture facilities provide really ideal conditions for diseases to proliferate.

An average farm, he said, could hold half a million fish, while a larger one can hold “upwards of a million.” Said Godwin:

We expect the abundance and effects of sea lice to increase as our coastal oceans warm. We need to improve the relevant policies both in Canada and globally so that our parasite management strategies in aquaculture are resilient to environmental change for both the sake of wild salmon but also for farmed salmon.

Hutchings tells the Examiner that Australia has been accounting for climate change and how warming waters affect aquaculture for a decade or more. Not so, Canada, where he says, “We don’t seem to have a climate change-related strategy for dealing with the management of our oceans.”

Hutchings says he hopes that the findings of their recent study will lead to more exploration of the effects that climate change will have not just on open-net pen salmon farming but all coastal industries.

[1] Sean C. Godwin, Mark D. Fast, Anna Kuparinen, Kate E. Medcalf & Jeffrey A. Hutchings. Increasing temperatures accentuate negative fitness consequences of a marine parasite. October 28, 2020. Nature Research: Scientific Reports (2020) 10:18467. https://doi.org/10.1038/s41598-020-74948-3

[2] The Healthy Bays Network is an alliance of “the St. Mary’s Bay Protectors, Protect Liverpool Bay, the Twin Bays Coalition representing Mahone and St. Margaret’s Bays, the Association for the Preservation of the Eastern Shore, with support from the Ecology Action Centre, the Atlantic Salmon Federation, and the Nova Scotia Salmon Association.”

[3] In her new book, “Not On My Watch: How a Renegade Whale Biologist Took on Governments and Industry to Save Wild Salmon,” activist and biologist Alexandra Morton, tells how the “sea lice years” began for her in British Columbia, and provides a powerful indictment of the open pen salmon farming industry and government collusion.

[4] Footnotes have been removed from the quotes used here, but can be found in the original document online.

[5] Footnotes have been removed from the quotes used here, but can be found in the original document.

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