What's happening to Atlantic salmon?

To find out more about what the ICES community is doing to understand the decline in salmon stocks we spoke to Niall Ó Maoiléidigh, the Chair of the new Diadramous Fish Committee.

How is ICES involved with North Atlantic salmon?

ICES has a long history of involvement with salmon and has had a specific salmon working group (Working Group on North Atlantic Salmon) since 1979.

"Generally speaking, salmon stocks are in decline in many parts of the North Atlantic"

ICES has been providing scientific advice to the North Atlantic Salmon Conservation Organization (NASCO) since it was established in 1983, with the objective of contributing to the conservation, restoration, enhancement, and rational management of salmon stocks. The advice ICES provides to NASCO is similar to that provided for other fisheries and stocks, and covers:

1 Fisheries and catches;
2 The status of stocks;
3 The expected abundance of stocks;
4 The conservation requirements; and
5 The catch appropriate to meet these conservation requirements.

Where the salmon advice differs somewhat from that for other species is related first to the large number of individual stocks (600 in North America and 1 500 in the Northeast Atlantic) for which advice must be provided.

Second, as the oceanic migrations of salmon cover a wide geographic area of the North Atlantic, this means drawing scientific expertise and information from all salmon-producing nations, from Canada and the USA on the North American side and from Russia to Portugal in the Northeast Atlantic. ICES also provides catch advice annually for the two high-seas mixed-stock fisheries of West Greenland (mainly North American and Southern European stocks) and the Faroes (mainly Scandinavian stocks).

About 25 scientists meet annually, through ICES, as the Working Group on North Atlantic Salmon; their report forms the basis for the advice to NASCO from the Advisory Committee on Fishery Management (ACFM).

What is the status of salmon stocks in the North Atlantic?

Generally speaking, salmon stocks are in decline in many parts of the North Atlantic. This is despite fairly restrictive management measures and reductions in fisheries and exploitation rates.

ICES reports on the status of salmon stocks in the North Atlantic, using "sea age" to distinguish between them, as the biological characteristics, migrations, and relative contributions to spawning potential can be very different among the various stocks. The two main "sea age" categories are:

1. Maturing salmon that will return to spawn in their native rivers after one winter at sea. These are called maturing 1-sea-winter or 1SW salmon.

2. Non-maturing salmon that remain at sea for more than one winter before returning to their native rivers to spawn. These are called non-maturing 2SW or multi-sea winter (MSW) salmon in subsequent years.

Starting in the Northwest Atlantic, there has been a consistent decline in recruitment over two decades in North America (Canada and USA) for both maturing and non-maturing salmon.

Fig.1 North American salmon stocks

This has most significantly affected the non-maturing component where recruitment is now less than the minimum recommended level - the so called spawning escapement reserve (SER) - needed to meet conservation requirements in North America (see Figure 1, right).


There has been a similar decline in recruitment of salmon (maturing and non-maturing) in Southern Europe (mainly Ireland, UK, and France) where these stocks are at or only just above the SER (see Figure 2, below).

In general, the overall situation for Northern European stocks (mainly Russia, Norway, Finland, Sweden, and Iceland) does not appear to be as severe.

Fig.2 Southern European salmon stocks

The main decline in recruitment has been shown for the non-maturing component of these stocks, although both components appear to be above the SER at present, with improvements noted in more recent years.

Why do you think that Atlantic salmon populations have declined?

Unfortunately, there is no one answer to this question. Certainly, marine survival, i.e. between the time of smolt migration from freshwater and the return of the adults from the sea, has been much lower than in the past.

There is a well-established relationship between marine habitat (measured as the relative index of the area suitable for salmon at sea using sea surface temperature data) and recruitment, which is statistically robust enough to forecast the abundance of salmon in any year prior to the fisheries.

However, "fish don't eat temperature" as one of our Canadian salmon scientists would remind us, so the exact mechanism by which salmon mortality is affected is not clearly understood.

There is some evidence emerging that sea temperatures affect migration speeds and routes and can affect the extent to which migrating salmon are killed by predators, as well as having more indirect effects on food availability.

The other main culprits to a lesser or larger degree have been overfishing, freshwater habitat deterioration, and various impediments to the upstream movements of adult salmon and the downstream migration of smolts.

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