BREMERHAVEN, Germany, Oct. 13 (UPI) -- Polar cod are a vital food source for whales, narwhals, ringed seals and arctic seabirds, but researchers have had a hard time studying these fish and estimating their numbers.
That's now changing, thanks to new netting technology. Recently, a team of German researchers were able to catch a large number of polar cod living beneath the arctic sea ice. Their findings suggest billions of juvenile cod prefer the shelter of the arctic shelves and drifting sea ice.
The researchers published their findings this week in the journal Polar Biology.
"For the first time, we've been able to use a special net directly below the sea ice to catch a large number of polar cod, and therefore to estimate their prevalence over a large area," Carmen David, a biologist with the Alfred Wegener Institute and first author of the new study, said in a press release. "If you extrapolate these findings, there could be more than nine billion polar cod living under the ice in the Eastern Arctic. What's more, we have also collected fundamental biological and physical data."
Until now, researchers were only able to to study a handful of polar cod at a time -- those caught beneath the sea ice by divers. Their new netting technology not only allows scientists to catch large schools of juvenile cod, but also collects data on ice thickness, temperature and salinity.
By tracking moving sea ice using satellite technology, researchers have also been able to estimate the paths of juvenile cod from breeding grounds to their wintering grounds. The trajectory of drifting sea ice suggests the polar cod follow the ice from the Laptev and Kara Seas northward into open seas.
"We analyzed the satellite data to determine how far the ice in that particular area has traveled," said study co-author Hauke Flores, an AWI biologist. "It took the ice between 240 and 340 days to travel from the coast to our measurement stations in the sea. These figures correspond with the age and size of the juvenile polar cod that we caught."
David, Flores and their colleagues are eager to understand how these young polar cod interact with other polar cod populations, as well as how they will be affected by climate change. As arctic waters warm, polar cod face new competition from species like Atlantic cod and capelin.
"We want to determine whether or not the young fish under the ice serve as a form of 'polar cod reserve,' increasing the overall chances of survival for the coastal populations through genetic exchanges with populations in Siberia and elsewhere," explained Flores.