Chris Gomersall/RSPB Images A large wreck of starving Northern Fulmars in Feb 2004 was the first indication of a major problem for the North Sea's seabirds Zoom In

Seabirds in the North Sea: victims of climate change?

05-01-2005

Researchers suspect climate change is undermining the supply of sandeels, and bears much of the blame for widespread breeding failure around the North Sea.

In February 2004, birdwatchers in eastern Britain were surprised by reports of Northern Fulmars Fulmarus glacialis inland, something highly unusual for a bird that normally winters far out at sea. Shortly afterwards, hundreds of dead Northern Fulmars began washing up along UK coastlines. Similar numbers were reported from France, Belgium, Germany and the Netherlands.

Post-mortems by the Alterra research institute in the Netherlands and the RSPCA in the UK revealed that the birds had died from starvation. Many of them had arrested or unfinished moult patterns, and around 90% were female.

"Healthy birds complete their moults long before February," explains Dr Jan van Franeker, Head of Alterra’s Fulmar project. "The stage at which moult has been interrupted shows these birds had encountered serious energy problems at least four to five months before they died."

C H Gomersall/RSPB Images Seabird colonies in the UK suffered alarmingly from a shortage of sandeels during 2004 Zoom In

"These birds had encountered serious energy problems at least four to five months before they died." —Dr Jan van Franeker, Head of Alterra’s Fulmar project

The fulmar wreck was only the first sign that things were going badly wrong for seabirds in the North Sea in 2004. Summer storms hit the breeding success of many species in the UK, including Atlantic Puffins Fratercula arctica. 1,000 dead chicks were found among the 2,000 breeding pairs of Sandwich Terns Sterna sandvicensis on the Farne Islands, after half the previous June’s total rainfall fell in just two days.

But the birds were already under severe pressure from a shortage of sandeels, the primary food source for the chicks of most British-breeding seabirds, and an important staple for adults.

At the RSPB (BirdLife in the UK) nature reserve at Sumburgh Head, Shetlands, Northern Guillemot Uria aalge breeding numbers were the lowest since monitoring began in 1977. No more than eight chicks were reared by the 108 pairs which tried to breed in the study plot. Egg laying began almost four weeks later than normal.

At Bempton Cliffs in Yorkshire, the RSPB estimated breeding success for Black-legged Kittiwakes Rissa tridactyla as just one chick per five nests, the worst output in nearly 20 years of monitoring. Normally at least one chick would be raised in every nest. The UK Government uses kittiwakes as an indicator of the state of the sea.

The British Isles holds 60% of the global population of Great Skuas Stercorarius skua, which also suffered unprecedented breeding failure. This species usually feeds its young on fish, but as stocks have dwindled over the last 20 years, they have begun to prey on other seabirds. This year many turned cannibal, eating each other’s chicks, and at most colonies no young were expected to fledge.

Paul G Morrison/RSPB A lack of sandeels in the summer of 2004 led to adult terns feeding their hungry chicks on unsuitably large prey, such as these pipefish Zoom In

2004 was the worst year on record for seabird colonies in the Shetlands and Orkneys

No Arctic Tern Sterna paradisaea or kittiwake chicks were reared in the south of Shetland in 2004. And although hundreds of Arctic Terns arrived at the RSPB’s Mousa reserve this spring, no young were fledged. All the large Arctic Tern colonies in Orkney failed, and for the first time in living memory, none nested at the RSPB reserve on Papa Westray.

By contrast, Roseate Terns Sterna dougalli on Coquet Island in Northumberland had a good breeding season, thanks in part to protection provided by innovative new nestboxes. But wardens sometimes had to intervene to prevent tern chicks choking, as parent birds tried to feed them unfeasibly large pipefish. Again, a shortage of sandeels was blamed.

The disappearance of sandeels has afflicted the UK’s North Sea coast from Yorkshire to Shetland, where the stock collapse was so severe that fishermen voluntarily shut down the fishery in the worst affected area. By contrast to the small local inshore fishery in the Shetlands, the huge (Danish-led) offshore sandeel fishery in the North Sea kept going but struggled to catch 300,000 tonnes of sandeels out of an annual quota in excess of 800,000.

What has caused the collapse of the sandeel population? In what scientists are labelling a "regime shift", rising sea temperatures have fundamentally changed the plankton mix, to the detriment of sandeels.

"We could be witnessing the single biggest change in the North Sea since it was formed 10,000 years ago." —Euan Dunn, Head of RSPB Marine Policy

"Sandeels prop up the marine food web, from cod and mackerel to kittiwakes. There is a compelling case for reining in the offshore commercial industrial fishery for sandeels even further," said Euan Dunn, Head of Marine Policy at the RSPB. The preliminary scientific advice for next year is to cut the catch limit by 60% due to the "historic low" sandeel stock level, a move greatly welcomed by BirdLife.

The change in the mix of zooplankton (copepods) in the North Sea may be having adverse effects beyond the summer breeding season. Northern Fulmars too rely heavily on plankton to get them through the winter. Although the factors behind the wrecks may be more complex, a poor summer for sandeels followed by reduced availability of winter plankton would have left the birds in dangerously vulnerable condition.

Ornithologists in the USA are investigating a similar wreck of Northern Fulmars along the coast from California to Washington in November last year.

A research vessel surveying waters between Britain and continental Europe reports other signs of an ecosystem in trouble: virtually no guillemot chicks, an unusual lack of cetacean activity between the Moray Firth and the Northern Isles of Scotland, and Northern Fulmars in poor plumage condition, once again showing evidence of arrested moult.

If these are symptoms of climate change, the situation is likely to get even worse in coming years. "We could be witnessing the single biggest change in the North Sea since it was formed 10,000 years ago," warned the RSPB’s Euan Dunn.