Every summer, 25,000 beluga whales converge on the Canadian side of the Beaufort Sea. Scientists had theories about what the whales were eating there but no hard data. That changed after a summer survey, reports CBC News.

The scientists realized that the Beaufort is actually a layer-cake of sea water with various temperatures and salinity. At about 200 meters down, water originating in the Pacific Ocean begins to give way to colder, saltier water coming from the Atlantic.

"It's a mixing zone," said Reist. "Mixing areas tend to be very species-rich and they also tend to be very productive. It concentrates the food and productivity in the area."

This zone was true to form.

"It provides the larder for one of the key species in the area — the Arctic cod, a small fish but a very pivotal one," Reist said.

Team members found the cod in "huge concentrations."