Scientists put faith in DNA tracing system as time runs out for wild Atlantic salmon

 

A last-ditch attempt to save the wild Atlantic salmon from extinction will use the latest DNA techniques available, The Times has learnt.

Researchers working on the Salmon at Sea (Salsea) project have described it as the final chance to determine why stocks of the fish have declined so dramatically. They hope that the groundbreaking decision to take DNA samples from fish in the Atlantic and trace them to the exact river or tributary they were born in will provide clues to their demise and help to revitalise the country’s £100 million recreational wild salmon angling industry. In the early 1970s about 12,000 tonnes of salmon were being landed annually, compared with just 2,000 tonnes in 2005. Mal-colm Windsor, the secretary of the North Atlantic Salmon Conservation Organisation, the intergovernmental body behind the multimillion-pound project, said: “Big offshore fisheries have been closed down, Irish drift nets have been banned, rivers have been cleaned, habitats are being improved. We have done everything we can possibly do: the only thing left is the sea.”

He added: “Time is not on the side of the wild Atlantic salmon and the point of no return is getting closer.”

Salsea, which is to begin its activities next year, will use specially adapted trawlers to track and count the fish in the ocean, something that has never been attempted before. Some of the salmon will be captured and microsatellites of DNA from their scales will be compared against a genetic atlas, allowing them to be matched with one of the 2,000 rivers and tens of thousands of tributaries in the northern Atlantic countries.

Mr Windsor said that because the salmon is an “aquatic canary”, signalling by its presence the quality of the water through which it migrates from freshwater rivers to shallow seas, deep oceans and back to its birthplace, the project could provide further evidence of the impact of climate change. “When we find the fish at sea we will know where it came from and the state of the stocks. We will find out about the salinity and temperature of the water they are in and whether climate change is the problem.”

Anglers in Wales, where about 400,000 visitors fish for salmon and trout each year, confirmed that stocks had been in unrelenting decline for years. Gethyn Thomas, of the Carmarthenshire Fishermen’s Federation, said there had been unconfirmed reports that trawlers from other European countries were landing migrating salmon illegally and hiding them under legally landed fish. “They come into the estuaries under the cover of darkness and they may be hiding the salmon,” he said. “It’s a policing matter and the government agencies are squeezed for cash. But I think there may be a lot of contributing factors. We are doing our best on the River Tywi with a restocking programme but it seems it is out of our hands.”

Garth Roberts, a fellow fisherman, added: “There have been several years of poor returns and there’s no underestimating the importance of salmon fishing to Wales.” In Scotland, salmon fishing on the River Tweed alone is estimated to be worth £18 million annually.

Ivor Llewelyn, the deputy director of the Atlantic Salmon Trust, said that the introduction of catch-and-release schemes had helped to slow the decline in the past couple of years, especially in Scotland. But he added: “There are still worrying signs for the future. There has been a dramatic fall in the numbers that are returning to spawn.”

Of further concern is the state of the stocks that do return to their birthplace. On some rivers, stocks are 30 per cent lighter, while the numbers of fish measured below the previous average length of 60cm (24in) is now five times what it used to be on some rivers.

Researchers fear that the salmon’s oceanic food sources of krill and shrimp, which thrive in deep, cold waters, are declining because of rising sea temperatures. There are also fears that the two million salmon that have escaped from fish farms in recent years are infecting wild salmon with lice and weakening their genetic identity through crossbreeding.

Mr Windsor said: “If we can halt this decline we can help regenerate communities in some of the remotest communities. Every river that the salmon returns to will be able to offer new opportunities and jobs – the salmon is a cash register.”

Fish and ships

— Salmon carry a genetic identity tag in each scale

— Analysis can detect the lineage of a fish and identify the river population to which it belongs

— A genetic atlas for the North Atlantic salmon population is in production Research vessels will record salmon numbers passing through nets

— This will provide a detailed picture of the salmon entering, living in and leaving its ocean environment

— Possible causes of declining numbers include: escaped farmed salmon changing genetic structure and diluting homing instinct, pollutants, global warming disrupting the food chain, parasites or predators, by-catch in the ocean fisheries for mackerel and herring, illegal fishing

Source: North Atlantic Salmon Conservation Organisation