The tens of thousands of lakes that dot the tundra of Alaska's North Slope are so similar that almost all are nameless.
But to the birds and fish that use them, there are differences of great consequence among the lakes, according to recently-published studies by scientists from the University of Alaska Fairbanks and the U.S. Geological Survey.
The lakes -- which freeze in winter, swell with the spring melt and dry out during the summer before starting the cycle again -- have characteristics that affect their suitability for yellow-billed loons, Pacific loons and fish of varying sizes, according to the studies. The loon-centric study was published in the May issue of the Journal of Avian Biology; the fish study, which had a co-author from the Bureau of Land Management, was published online in June in the journal Freshwater Biology.
To gather data on loons and fish, the scientists camped out on the tundra for varying periods over four summers, said lead author Trevor Haynes. They moved every two days, hopping lake to lake by small plane and setting up and breaking down camp sites enough times to examine fish in 86 lakes, a process that required pulling up fish with a variety of nets and traps. While at the sites, they also located and documented loons, filling in data that could not be gathered from aerial surveys, Haynes said.
That is because the larger yellow-billed loons dominate the smaller Pacific loons and claim the bigger lakes, Haynes said.
"Loons are very, very territorial animals and, as with most things in the animal kingdom, body size determines who gets pushed around," he said.
Loons can be fierce when defending territory, sometimes fighting to the death over turf, Haynes said. His team did find one dead Pacific loon on a lake shoreline, apparently the victim of such a fight, he said. They also witnessed, from a distance, some of those clashes, which features by "a lot of splashing and a lot of calling," Haynes said.
Smaller lakes are suitable for the smaller Pacific loons; they are lighter, eat less and need less surface area for taking flight or landing, he said. But for yellow-billed loons, currently under consideration for Endangered Species Act protections, significant lake dry-out poses problems. "A yellow-billed loon is probably going to have a hard time on a smaller lake," he said.
Many Arctic lakes are shrinking, a trend partly attributed to the warming far-north climate. A 2005 study published in Science documented widespread shrinkage among more 10,000 Siberian lakes tracked by satellite.
That trend can be seen in Alaska as well, Haynes said. "If you fly over the North Slope, you'll see big swaths of area where lakes have dried, or you'll see a lake that has shrunk to an eighth of its original size," he said.
Among fish that use the North Slope lakes, small and hardy species like ninespine stickleback had the least trouble colonizing lakes, the fish study found. Those fish were found in lakes that freeze solid over the winter as well as those retaining liquid water year-round, and in lakes with or without stream connections.
"It just seems like stickleback are everywhere," Haynes said.
But larger fish tended to be more restricted and dependent on connections between water bodies, like those created during the springtime flush, when "there is a great opportunity for everything to move around," Haynes said.
While stickleback and Alaska blackfish are able to spend entire winters in the unfrozen depths of the lakes, other species need seasonal connections to wintering sites in rivers or possibly marine waters, the study found.
If those connections dry out too soon, the bigger fish can be in trouble, Haynes aid.
A drying-out trend similar to the one in Siberia has also been found in Alaska regions south of the Arctic Circle. A 2003 study by UAF scientists found shrinking ponds in the discontinuous permafrost near the northwest Alaska community of Council. Another UAF study, published in 2009, documented half a century of shrinkage in ponds in various parts of subarctic Alaska, including the Kenai Peninsula and Seward Peninsula. The changes were attributed to increased evaporation caused by warmer temperatures, increased drainage caused by permafrost thaw, or a combination of the two.
However, Haynes points out, some lake changes in permafrost areas are part of the natural cycle, unaffected by climate trends.
And lake changes are not always in the same direction, studies have shown. The study of Siberian lakes, for example, found that in the northwestern part of the study area, some new lakes had appeared and some existing lakes had expanded.