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Northern gannets are here to stay in Svalbard

Two couples of gannets established themselves at Bjørnøya in 2011. This year, it registered more than 60 individuals. FOTO: Rob Barrett / Tromsø museum

Northern gannets are here to stay in Svalbard

The population on Bjørnøya is growing.

Two pairs of the seabirds established themselves as the first nesting occupants of Bjørnøya in 2011.

The population since then has skyrocketed, according to Hallvard Strøm, a Norwegian Polar Institute researcher responsible for studying seabirds on the island.

"This year we registered 25 breeding pairs and more than 60 individuals at the high point," he said after this year's fieldwork. "This year there will be probably a good offspring production."

Coexisting
Northern gannets have settled at Alkeholmen at the southern tip of the island, where they share space with about 30,000 guillemots and fulmars.

"But with its superior size, that is not a problem for the gannets," said Strøm, adding he does not believe the newcomers will oust the "old" species at the site.

"There is a lot of vacant land on the island and they are taking advantage of larger prey than the other seabird species in Svalbard," he says. "They eat more fish than the others."

But exactly what they are eating remains a mystery.

"They live only at Alkeholmen and that is relatively impregnable with its steep sides," Strøm said. "Therefore, we have not reached there ourselves to investigate them further. We must content ourselves with observing from afar with telescopes."

The growth we are seeing now is so fast that it can not be about reproduction by chicks that are are born on Bjørnøya


Unknown diet

Herring, mackerel, pollock and capelin are key prey for gannets on the mainland. The birds catch them by diving down into the water at speeds around 100 km/h.

"It is tempting to believe that the capelin is important for their Bjørnøya portfolio, as it is for most other seabirds on the island," Strøm said. "The fish are swallowed whole and regurgitated again when the parents come back to the youngsters in the nest."

Northern gannets are not only new in Svalbard, but in the kingdom.

The first colony was established at Runde in 1946 and since then they spread northward. Strøm said he believes they will become increasingly prevalent on Bjørnøya during the next decade.

"The growth we are seeing now is so fast that it can not be about reproduction by chicks that are are born on Bjørnøya," he said. "They do not reproduce until they are four to six years old. These are birds that come from elsewhere and settle down, but we do not know from where."

Complicated

The reason they – like many other species – are coming northward is uncertain.

"Whether the gannets establishing themselves in Svalbard is related to warmer climates is difficult to say because of the expansion they've had during the past 70 years," Strøm said. "It's probably a mixture of several different reasons, but warmer oceans are hardly a disadvantage."

He promises there will be more research about the species on Bjørnøya in the coming years.

"Now they're part of our regular monitoring," he said. "We have a good overview of the islet and we will probably consider whether we should go up there. But so far it is not appropriate."




Translated by Mark Sabbatini

Se bildet større

The species have settled on Alkeholmen, which is very difficult to access for researchers. FOTO: Hallvard Holm, Nowegian Polar Institute

Se bildet større

Havsula have settled among 30,000 guillemots and fulmars. Alkeholmen is quite similar to nesting sites they use in the south. FOTO: Hallvard Holm, Nowegian Polar Institute

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