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It’s boom time for large whales in the Arctic – an unexpected benefit of the unprecedented sea ice reduction seen in the region over the past 30 years.

at the National Oceanic and Atmospheric Administration in Seattle has analysed 30 years of whale survey information gathered in the Chukchi Sea – which separates Russia and Alaska – and the surrounding area. She realised that three species of plankton-eating baleen whales – humpback, fin and minke – are now routinely spotted in the region, even though surveys in the 1980s never encountered these species there.

The population of bowheads – a baleen whale native to the Arctic – may also be thriving, according to Moore’s analysis.

This rise in whale sightings coincides with the loss of sea ice. “Millions of square miles of sea ice has been lost in the past decade,” says at the University of Oxford. “If you take the last 30 years alone, that’s 10 per cent per decade. It’s unbelievable.”

The lack of ice leads to extraordinarily favourable growing conditions for zooplankton – which is a good thing for the baleen whales that eat them, says at the University of St Andrews in the UK.

More light can penetrate into the surface water of ice-free oceans, fuelling blooms of phytoplankton and the zooplankton that graze on them.

Nutrient levels also increase. “Wind driven across the now open sea surface causes water to mix,” says Miller. “This brings nutrients up from depth.”

Ice-free normality

Some believe the Arctic has entered a “new normal” in which there is permanently less sea ice. “We are seeing a transition because the sea ice there is still declining. What is certain is that this warming allows the existence of some species, and the decline of others,” says Macias-Fauria.

Baleen whales might be benefitting in particular because there are so few steps in the food chain separating them from the phytoplankton. “For instance, bowhead whales are only removed by one step,” says Miller. “The zooplankton feed on the phytoplankton and the bowheads eat that zooplankton.”

That said, the boom may be echoing higher up the food chain, too. Toothed cetaceans like orcas and sperm whales appear to be becoming more prevalent at higher latitudes, says Miller, moving in to predate on the larger baleen whales.

It’s not just population numbers that are booming. Last year a team led by Craig George at the Department of Wildlife Management in Barrow, Alaska, found evidence that the , possibly because of the increased availability of food.

As with so many things in the natural world though, this boom looks set to be finite, says Macias-Fauria. “In the past three or four years this productivity increase seems to have reached a halt,” he says. “It’s not decreasing, but nor is it increasing. At a given point you cannot keep on increasing productivity, because you just end up exhausting the nutrients in the water.”

The ice-free waters are also attracting more human attention – and the noise from our marine activities may have a detrimental impact on Arctic whale populations in the longer term.

Read more: What ice-free summers will mean for Arctic life