King of fish threatened

THERE are few natural predators capable of catching a fully grown mature salmon. A dolphin is capable of hunting down the king of fish but would probably prefer easier prey; seals are a risk in confined areas where the salmon can be trapped, particularly during colder months. But this powerful creature, when fully grown, is superbly equipped to out-swim almost anything else in the sea.

Humans also pose only a limited threat: it is only "lightly fished" and while a few are caught in nets meant for the likes of mackerel and herring this is not thought to make a significant dent in their numbers.

So it may come as a surprise to some to learn that when salmon leave Scotland's rivers and travel to traditional feeding grounds in the Norwegian Sea and off Greenland, they are being slaughtered as never before.

Forty years ago, nearly half the smolts leaving freshwater for salt would return to breed. Now as few as 10 per cent of fish are succeeding in making the same journey.

And, according to a new study of returning fish, there is further bad news: those that do return are becoming thinner and thinner. This is alarming because salmon stop feeding and rely on fat reserves to make their epic trip back to the headwaters of their birth river to breed. The females also rely on stored fat to make eggs.

The reason for this alarming picture appears to be changes in the distribution of plankton populations - caused by climate change - which mean there is less food for the salmon while at sea.

Surveys of the numbers of salmon going out to sea and returning have been carried out on the North Esk since 1964 by Fisheries Research Services staff. Scientists have noted a "marked upward trend in marine mortality rate over the period in which monitoring was carried out" (see graph).

And the new study by Professor Chris Todd of thousands of grilse - young salmon which have spent a single winter at sea - found that over the last ten years, the average weight of the fish fell by 11 to 14 per cent.

Prof Todd, a marine ecologist at St Andrews University who was speaking at an Atlantic Salmon Trust conference on the fate of salmon at sea in Edinburgh yesterday, told The Scotsman: "Our analyses indicate that this is closely linked to ocean climate warming in the north-east Atlantic. Probably we are seeing the effects of a lack of feeding for salmon at sea, arising from temperature-driven shifts in the distribution of the plankton communities upon which salmon depend.

"It is likely that the salmon still are migrating to the correct part of the ocean, but when they get there the food simply is not available to them."

The worst affected are up to 30 per cent underweight and fat reserves have been found to be 80 per cent below those of a salmon in good condition.

"To ensure the future of wild salmon in an ever-changing environment we do need to especially encourage anglers to release as many females as possible to give them a chance of successfully spawning," Prof Todd said.

Some might think the decline of the salmon is being linked to climate change by those eager to convince the public of the need to cut carbon emissions. But Richard Shelton, research director at the trust, does not believe in "anthropogenic" global warming and is convinced the changing climate is the salmon's main problem. He cited seals, sea lice from fish farms and bycatch by fishing boats as factors, but said: "My own view - and I think it is the view of nearly all the marine scientists who have looked into it - is if there is any one reason, it is problems finding food relatively early in their lives driven by changes in the marine climate.

"There is no short-term answer to it even if you believe anthropogenic forces are the main reason behind climate change and I don't believe that."

A lack of food means the marine salmon are finding it increasingly difficult grow into the giant super-fish it is capable of becoming. A smaller, weaker, slower salmon is easier prey.

"Fish just don't die of old age at sea," Dr Shelton said. "They die of being predated one way or another or being caught by a fishery. The longer you are small, the greater the range of predators capable of catching you."

The Scotsman's manifesto to protect the seas

THE Scotsman has launched a campaign for urgent steps to be taken to protect our precious marine life.

We want:

• a network of marine reserves and protected areas to be created to safeguard properly sites such as St Kilda, one of just 30 marine World Heritage Sites, the Sound of Mull, an important area for whales and dolphins, and Loch Sween with its lagoons and tidal rapids;

• a system of marine planning, effectively zoning areas for appropriate use, to safeguard important fishing grounds from offshore wind farms and other developments and allow humans to exploit the seas in the most sustainable way;

• a single marine management organisation for Scottish waters to ensure this system operates as efficiently as possible;

• Scotland should also be given control of conservation to the 200-mile boundary with international waters. At present, the Scottish Government controls out to 12 miles, with the UK government responsible for the waters beyond that.