What's Happening to Atlantic Salmon
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. 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:
- fisheries and catches;
- the status of stocks;
- the expected abundance of stocks;
- the conservation requirements; and
- 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:
- 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.
- 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. 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).
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). In general, the overall situation for Northern European stocks (mainly Russia, Norway, Finland, Sweden, and Iceland) does not appear to be as severe. 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.
Do salmon get caught as a by-catch in marine fisheries?
We are becoming increasingly aware of the possible impacts of marine fisheries on salmon survival, particularly at the post-smolt stage (up until August/September of the first year at sea). For some years, the Norwegians have been developing techniques to sample post-smolts at sea using modified surface trawls. This work has provided us with some exciting new insights into the oceanic migrations of European salmon in the first few months at sea when mortality rates are likely to be very high.
One of the more significant findings from this experimental work has been that post-smolt catches are generally made with large mackerel by-catches. This has raised the possibility that similar commercial trawl fisheries for mackerel in the same areas could also be taking post-smolts. Initial estimates provided by the Working Group in 2002 suggest that this could be a significant proportion of the total recruits available. It is certainly an area of investigation, which we need to pursue in association with our colleagues in other fisheries Working Groups.
Have there been any recent breakthroughs in our understanding of salmon life histories?
The whole area of marine survival has been regarded as a "black hole" until very recently. Studies undertaken, in particular by Norwegian and Scottish scientists, to design and set up marine sampling programmes have paid enormous dividends in a relatively short time. These studies have provided new information on migration routes, timing, and oceanographic factors, which influence the early migrations.
These studies have been complemented by highly innovative work in North America and Europe using data storage tags on kelts (spent salmon returning to sea after spawning) and nearshore tracking systems, again using new electronic tags. We have also learned a lot recently by better use of existing data in new modelling and simulation approaches, particularly in the Northeast Atlantic area which has had the benefit of nearly three years of an EU-funded concerted action (SALMODEL: A coordinated approach towards the development of a scientific basis for management of wild Atlantic salmon in the Northeast Atlantic).
While a lot is happening or beginning to happen, it will take some time to bring all of this new information into a more global understanding of the key processes involved in salmon migration and marine survival. But the first steps are now being taken.
How do you think the current decline in salmon stocks could be halted?
One of the worrying features of the continuing decline in recruitment is that despite all the very significant closures or restrictions in fisheries on both sides of the Atlantic and in the mixed stock high-seas fisheries of West Greenland and the Faroes, the expected benefits from these measures have not materialised in all areas. Obviously, without these measures the situation would be even worse, but it must be acknowledged that there have been huge efforts in recent years to allow more fish to spawn.
While marine conditions for salmon have shown some improvement in recent years -- in terms of more sea area with optimum temperatures -- it appears that the expected response from the stocks to this increase has been slow or has not yet occurred. Clearly, we need to give salmon stocks every chance to respond to the improved conditions and this can only be done by meeting conservation limits. This is likely to mean even greater restrictions in fisheries, and in some areas stock rebuilding will be necessary. While it is important to understand how marine conditions affect mortality, action must be taken to ensure the best use of the stocks that are available.
For further information please contact Niall Ó Maoiléidigh at:
Salmon Management Services Division
Marine Institute
Abbotstown
Dublin 15
Ireland
E-mail: niall.omaoileidigh@marine.ie
Atlantic salmon life cycle
Eggs: Pea-sized orange eggs are deposited on the riverbed in the autumn.
Alevin: Salmon alevin emerge and hide from predators in the riverbed gravels. They are 2 cm or less in length.
Fry: The young fish wriggle up into the water column, and are called fry.
Parr: When the fry reach a length of 5–8 cm, vertical markings or parr marks appear. Parr remain in the river for 2–6 years.
Smolt: At a length of 12–24 cm, a silvery sheen replaces the parr marks and the smolt’s body and physiology changes to allow it to survive in saltwater as it moves down river to the sea.
Post-smolt: From the entrance into the sea and up to their first sea-winter the young salmon are called post-smolts. Adult:
Adult salmon live in the sea for 1–2 years. They then move into their native rivers to spawn, after which most of them die.
Kelt: A “spent” salmon returning to the sea after spawning.
Pull quotes: “We are becoming increasingly aware of the possible impacts of marine fisheries on salmon survival, particularly at the post-smolt stage”.
“While marine conditions for salmon have shown some improvement in recent years—in terms of more sea area with optimum temperatures—it appears that the expected response from the stocks to this increase has been slow or has not yet occurred”. newItem
Images:
Figure 1: Salmon recruitment in North American stocks over the last 30 years showing how it has remained below minimum levels since 1993.
Figure 2: Salmon recruitment in Southern European stocks over the last 30 years showing how it has remained below or close to minimum levels since 1996.
Photo 1: caption: "Generally speaking, salmon stocks are in decline in many parts of the North Atlantic." Photo credit: Photo from Erling Svensen www.marinbi.com
Photo 2: caption: "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." Photo credit: Photo from the Natural History Photo Agency (www.nhpa.co.uk)
