There has already been a great deal of speculation on how global warming could affect the North, and researchers have looked at the impacts of climate change on everything from caribou to trees to peatlands. A federal fisheries biologist wants to add fish habitat to that list.

Al von Finster works with the Habitat and Enhancement Branch of Fisheries and Oceans Canada in Whitehorse. He has put out a discussion paper that he hopes will get people to think and talk about how climate change could affect the drainages in the Yukon River Basin. The paper is not based on hard research, but on the overview he has from working in the Yukon over a long period of time.

"I wanted to synthesize my experience from working in the Yukon for 16½ years. In my job I cover a wide area and I'm not able to go back into the same area year after year, but when I do revisit an area I can see changes that have taken place," he says.

Von Finster uses an example from the Tatshenshini River. When he first visited there about ten years ago he noticed that a number of small unnamed streams near the confluence of the Tatshenshini and the Alsek Rivers were loaded with silt from melting glaciers.

When he returned a few years later, he noticed that the water in some streams had cleared, and salmon had moved into them. This change is probably due to the fact that the glaciers have already melted back from the edge of the river, and are no longer a source of silt.

Von Finster speculates that as the ice caps and glaciers in the Coast Range continue to melt, more water will flow into lakes such as Atlin, Bennett and Tagish. The higher water levels in the lakes will last longer through the summer, affecting habitats along the shorelines. As the melting of glacial ice slows down -- as it has already in places on the Tatshenshini River -- the lake levels would change again.

The list of possible effects on fish habitat is a long one because fish live in so many different environments. Also, there could be winners and losers as a result of climate change.

Salmon could find new habitat on streams that clear because there is less glacial sediment in them, but salmon that spawn in small streams not fed by glaciers could be less lucky. They might not be able to reach their spawning grounds if water levels go down.

Lower water levels in small streams could make it easier for beavers to build dams. Then, if less water flushes down the river in the spring, fewer dams will be washed away, changing habitat once again.

Von Finster says that some streams in the Whitehorse area have had lower water for a few years already, though it is not possible to say whether climate change is directly responsible. One example is Judas Creek, which dried up in spots in the summer of 1998.

Melting of ground ice and permafrost could have a considerable impact on small streams. As ice melts it releases organic material into the streams, which can in turn tie up the available oxygen in the water. All of these factors feed back on each other, and sorting out the possible effects is no easy task.

Von Finster thinks that this complexity is one of the reasons why very little work has been done on inland fish habitat.

A great deal of climate change research has focussed on ocean environments, which he believes to be less complex than inland habitats.

Large water masses such as the El Nino current are fairly homogenous, so multidisciplinary teams of scientists can track changes within the currents while working together aboard research ships. In inland areas, biologists and other investigators tend to focus on their own specific research, and information is not gathered together for a more holistic picture of the environment.

Von Finster says that some people have taken exception to some of his approaches, such as his assumption that precipitation will not change. He says he kept his scenario general because it would be impossible to factor in every possible change in a discussion paper.

"The scenarios get very complicated. Suppose an extra inch of rain falls in June when air temperatures are high and all of the plants are growing. Lots of that moisture would return to the air through evapotranspiration," he says. "If the same thing happened in September, the water would go into the ground and be available the next year. So the effects of the rain on streams would be greater if it fell in September."

Von Finster says he is not attempting to predict how climate change will affect inland water systems. He just wants to get people thinking and talking about the subject, and welcomes comments of all types, including challenges to the scenarios that he paints.

The discussion paper, titled "Possible Effects of Climate Change on the Physical Characteristics of Fish Habitats in the Yukon River Basin in Canada," is available on Taiga Net. Al von Finster can be reached at Fisheries and Oceans Canada in Whitehorse.