Donal Hickey: The sea has the answer to dwindling salmon stocks

By Donal Hickey

AS most Irish and European rivers are now closed for normal, wild salmon fishing, a respected Norwegian salmon scientist has called for new thinking on why stocks are seriously dwindling.

Dr Jens Christian Holt challenges reasons cited, in recent years, for the decline, which include climate change, sea lice from salmon farms, crossbreeding with farmed salmon, and the unintended catching of salmon by trawlers. But, from his research over three decades, he believes overfeeding and predation are major factors behind diminishing salmon and sea-bird stocks in Western Europe. He says Atlantic mackerel stocks have grown out of proportion, leading to excess demand on the food of whales, seals, sea birds, salmon, and mackerel itself.

This lack of food has also led to starvation and very slow growth of young salmon at sea, which are now more vulnerable to predation and disease than before the mackerel “explosion”. For instance, a young salmon from the Corrib catchment, in the west of Ireland, makes a perilous journey to the Norwegian Sea feeding area, swimming alongside hungry mackerel during its 2,000km migration.

Irish and British salmon stocks have diminished more than Norwegian stocks, despite 1.3m tonnes of salmon being farmed in Norway and only 200,000 tonnes in Ireland and western Scotland. Dr Holt says that southern salmon have to travel for much longer distances than the average Norwegian young salmon and are therefore at greater risk of becoming mackerel prey.

He also says today’s fish-farming practices are unsustainable and should change to enclosed or semi-enclosed systems, for environmental reasons and the sustainable growth of the industry. “Sea lice is a factor for the marine survival of salmon in some areas, but it is a relatively small factor today and should not be the point of focus in the recovery of European salmon stocks,” he adds.

Following two years of successful mackerel-spawning, in 2016 and 2017, in the Norwegian Sea and Norwegian coast, these waters are now full of juvenile mackerel. Consequently, the worst may be yet to come for salmon from the southern European salmon regions. Parallel with the European salmon collapse is a collapse in the number of western European sea birds that depend on plankton, fish larvae, and small fish for their food. The worst-hit species is the kittiwake, which is numerous on the Skelligs, off Kerry, and which competes with mackerel for its food.

Much is unknown about salmon at sea and Dr Holt says there’s been too much of a focus on what’s happening in rivers and coasts. We must look out to sea for a new view on why salmon and seabirds are not as numerous as they were.