CODY - Yellowstone National Park managers are moving forward with a plan that will allow entry each day of up to 318 snowmobiles and 78 snow coaches when the park opens for the winter season starting on Dec. 15.

A federal appeals court is expected to hear oral arguments Friday in an ongoing legal dispute between environmental groups and snowmobile advocates over how many sleds should be allowed in the park.

Daily limits during the last several years have ranged from 540 to 720. But separate rulings from federal judges in Washington, D.C., and Wyoming have left managers with a current court-imposed maximum of 318.

Record numbers

Visitors came to the park in record numbers this summer, but planners are unsure what is in store for the winter season, said Colin Campbell, a deputy superintendent for Yellowstone who spoke Monday to a group of Cody business leaders.

Last year's winter numbers were down from previous years, probably due in part to uncertainty among visitors over how a disputed winter-use plan might have affected their travel plans, Campbell said.

Only about 7 percent of visitor days in the 2008-09 winter season would have exceeded a cap of 312 snowmobiles, while about 35 percent of the 2007-08 season would have exceeded that same limit, he said.

Campbell said that park planners are continuing to work on a new environmental assessment of winter use that involves measuring and monitoring predefined parameters of how visitors affect everything from air quality to wildlife.

"Our best science right now tells us that the impacts from snow coaches and snowmobiles are about equal," he said.

Animal studies

"Wildlife is not significantly disturbed by either device traveling through the park," he said, adding that studies have shown that animals retreat or show a serious disturbance from winter vehicles in about 2 percent of cases.

Management operations on Sylvan Pass this winter will be similar to those last year, when the 70-day season saw 17 days when the pass was closed due to avalanche risks.

Park workers will employ a combination of forecasting and avalanche mitigation using a howitzer gun, as well as a helicopter contractor using hand charges, he said.

"Last year was a very challenging year on Sylvan Pass," Campbell said.

There were 149 avalanches along the pass, compared to 79 the year before. Of 52 slides that reached the road, 35 were deliberately triggered, he said.

Under an agreement reached between the National Park Service, Wyoming, Park County, the city of Cody and others seeking to maintain winter access over Sylvan Pass, the route will be open from Dec. 22 to March 1.

Some critics of the avalanche control program have said that its annual cost of hundreds of thousands of dollars is not justified by the relatively low number of Sylvan Pass visitors, a few hundred each winter.

Local residents have said the issue of winter access over the pass is important, regardless of how many people use the route, and that efforts to build visitor numbers have been hampered by annual uncertainty over winter plans.

Contact Ruffin Prevost at rprevost@billingsgazette.com or 307-527-7250.