The science of sustainable seafood, explained

Experts Weigh in on Farmed Salmon Escape in Washington State

A few weeks ago in Puget Sound, a net pen used for farming Atlantic salmon broke and allowed over 150,000 salmon to escape. Fear of these non-native fish interfering with native salmon have led to questions on potential impacts and a call to reevaluate salmon farming policy in Washington State. In particular, many Native American and First Nation Tribes (most of which are reliant on wild salmon fishing) have called for an end to farming salmon in Puget Sound.

Below we feature two comments on the situation. The first, by Casey Ruff, gives a Tribal perspective on the situation; the second, by Carl Walters focuses on the scientific implications.

Comment by Casey Ruff, Skagit River System Cooperative

While there is certainly some very compelling evidence from previous work quantifying negative effects of Atlantic salmon net pen aquaculture via transfer of parasites, from my limited knowledge of existing literature, I am aware of only one instance where there was evidence of successful natural spawning of escaped Atlantic salmon in the wild. There have been accidental releases of Atlantic salmon from net pens in the past, and individual adult Atlantic salmon associated with these releases have been observed in tributaries in the Skagit River during the fall time frame. To be clear, these fish weren’t observed spawning. Unfortunately, there wasn’t any coordinated monitoring effort that occurred as a result of these earlier accidental releases, so nothing was really learned in terms of the potential impact of those earlier release groups on wild populations. Therefore, while I am generally concerned about the potential risks of accidental escapements of Atlantic salmon to threatened populations of Puget Sound salmon stocks via interbreeding, competition/predation, or disease transfer, unfortunately we just don’t know a lot about the long term effects of escaped adult Atlantic salmon on wild Puget Sound salmon stocks.

For this incident, both state and tribal agencies are coordinating existing monitoring efforts to include sampling protocol for any adult or juvenile Atlantic salmon encountered. The sampling metrics include collection of diet samples, scales and otoliths for aging purposes and identifying the origin of the fish, kidney and spleen samples, pathology samples, length and weight for condition factor, and tissue samples for DNA confirmation of species which will be important should any juveniles be encountered.

Luckily, there are a number of River systems in the Puget Sound such as the Skagit River with existing adult and juvenile monitoring frameworks including nearshore, estuary/delta, smolt traps and spawning ground surveys. I would hope that the existing monitoring frameworks would allow some inference to be made regarding the long term impact of this particular release. Specifically, spawning ground surveys in the fall should allow the detection of any spawning activity by Atlantic salmon and subsequent smolt trapping and juvenile monitoring in the delta/estuary and nearshore would hopefully enable the detection of successful reproduction. As of Tuesday, September 5, there were approximately 186,000 Atlantic salmon unaccounted for; they are being encountered in river systems throughout the Puget Sound. In the lower Skagit River for example, at least 50 adult Atlantic salmon have been caught in tribal net ceremonial subsistence fisheries targeting Chinook salmon and coho salmon test fisheries. Thus far, all of the Atlantic salmon sampled in Skagit River have had empty stomachs which would indicate that these fish aren’t feeding at all. Hopefully we can learn something from this coordinated monitoring effort that will help inform the assessment of risk of Atlantic salmon aquaculture to Puget Sound salmon stocks.

Regarding actions that could reduce the risk of accidental adult escapement in the future, it seems that the existing net pens in Puget Sound are placed in areas with significant tidal exchange to help minimize the risk of the risk of disease transfer of parasite colonization. However, this increases the risk of accidental escapement of adults as a result of the combined effect of a compromise in the net pen structure and a large tidal event as occurred with the current escapement incident from the Cooke net pens. So in effect, they are trading one risk, which has been quantified to some degree, for a lesser understood risk.

In Puget Sound, wild Chinook salmon stocks area threatened under the Endangered Species Act and therefore have the potential to limit both terminal and mixed stock fisheries coast wide on any given year. It seems that given the present unknowns regarding the risks of escaped adult Atlantic salmon to native salmon stocks, my preference would be that regulatory actions require existing Atlantic salmon net pen operations in Puget Sound marine areas be discontinued or at a minimum not be allowed to expand, as was being evaluated by state agencies up until the recent accidental release incident. Land-based aquaculture programs would certainly be preferable, although my knowledge of different possibilities is extremely limited.

Casey Ruff is the Director of Harvest Management for the Skagit River System Cooperative.

Comment by Carl Walters, University of British Columbia

We have been farming Atlantic salmon in B.C. since the mid-1980s, and there have been many escapes but little evidence of successful reproduction.

There remains a legitimate concern about diseases. There have been repeated warnings in B.C. about sea lice. More worrisome are viral diseases: Infectious Salmon Anemia (ISA) has been found in B.C., and so has Heart and Skeletal Muscle Inflammation (HSMI). Fortunately, there is as yet no clear evidence that these diseases have persistently impacted survival of native salmon species. There have been various attempts to correlate the declines that we have seen in marine survival rates of some salmon stocks with fish farming, and this worked about as well as other correlative studies of salmon survival—the rule seems to be publish quickly, before your correlation breaks down.

For a good review of the history of Atlantic deliberate introductions and escapes in Washington and BC, and lack of evidence of their establishment in any of our streams, see here.

Carl Walters is a Professor Emeritus at the Institute for the Oceans and Fisheries at the University of British Columbia.

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