Linda Deegan, a senior scientist at MBL who studies an arctic fish called the grayling, doesn't need to see temperature stats to know that the climate around Lake Toolik is changing. She just has to check her travel calendar.

When Deegan started coming to Toolik in the 1980s, scientists like herself who are interested in water didn't get to station until late June or early July. In recent years the ice out date has gotten earlier and earlier and she now arrives earlier and earlier to do her science. We spent the day with her on the Kuparuk River today, testing the water for nutrients and insects.

Deegan has noticed a dramatic difference in the grayling population on the Kuparuk. In the mid-90s, when she strung a net across the river for two weeks, she'd collect 2,000 to 3,000 fish. When she did the same test a few years ago, she only caught 700.

"The biology is telling us that the system is changing," she said.

She believes the culprit is a number of dry years that are causing the rivers to dry out in spots. Grayling, like all arctic fish, must get out of the rivers during the winters because they freeze solid. Some fish, like salmon, head to the oceans. Others, including the grayling, swim to deep lakes that retain open water below an icy surface. But if the rivers don't run straight through to the lakes the grayling can't reach their winter homes and they die.

The overall population of grayling in the arctic is healthy, Deegan said. But she's worried that if the Kuparuk population gets hit with many more drought years, they may fall below sustainable levels.

Deegan is also interested in what the earlier ice out dates will mean for trout, which prey on the grayling in their winter lakes. Trout need light to feed, so the start date for their hunting is fixed. (Global warming doesn't change the cycle of daylight, of course.) So if the rivers warm up sooner and sooner and the grayling take off into the rivers sooner and sooner, the trout will have fewer days in which to eat.