Great Cormorants enjoy warmer Arctic seas

Populations of Great Cormorants in Arctic waters have grown as sea ice has retreated and the sea surface has become warmer, University of Birmingham scientists have found.

A study of sea surface temperatures and cormorant populations over half a century showed that on average the birds' numbers increased in warmer winters and decreased in relatively colder years.

The findings suggest that cormorant populations in the region are likely to increase as the climate continues to warm.

An international team of researchers, led by Professor Graham Martin from the University's Centre for Ornithology, looked at data on breeding populations of the Great Cormorant, Phalacrocrox carbo, at Greenland's Disko Bay, to understand exactly how strong the link is between sea temperatures and bird numbers.

They compared annual variations in sea temperatures with population data for 67 cormorant colonies in Disko Bay and adjacent areas for the period 1946 to 2005. The scientists found a positive relationship between winter sea temperatures and the rate of population change in the cormorant colonies. The highest rates of population change corresponded with periods of relatively high sea temperatures in recent years and during the 1960s.

For every degree Celsius increase in ocean temperature the cormorant population increased by 6.4 per cent. So in an average year – one with no variation in SST – the cormorant population will decrease by 1.5 per cent, but in a year that's 1°C warmer than average, the population will increase by 4.9 per cent.