NATURE

Tropical fish in winter

SUZANNE ZWARUN February 4 1985
NATURE

Tropical fish in winter

SUZANNE ZWARUN February 4 1985

Tropical fish in winter

NATURE

In Alberta's Rocky Mountains. January temperatures drop to as low as -50°C, and biologists estimate that

many thousands of animals protected from human hunters in the province’s national parks starve and freeze to death in the bitter winter cold each year. But in the extensive Cave and Basin hot mineral springs at the base of Banff’s Sulphur Mountain, fish thrive in water that averages 30°C year-round. Indeed, three of the species of fish in the sulphurous marsh are native only to tropical waters.

Dr. Joseph Nelson, a University of Alberta zoologist, has just completed a three-year survey of the Cave and Basin hot springs. Nelson traced the lineage of sailfin mollies and jewelfish to aquariums in Banff, 1.5 km away. The owners have deposited tropical fish in the hot springs over several decades. They have also transplanted tropical tape grass and bushy pondweed from their tanks into the marsh. It too is thriving, in clear violation of park policy, which forbids interference with local plants and wildlife.

Banff’s mollies originated in waters that drain into the Gulf of Mexico and the jewelfish come from Central Africa. But Nelson also counted thousands of mosquitofish—a species that park officials introduced from California in 1924 in an ultimately fruitless effort to control the mosquitoes that plagued bathers using the hot springs. He also found two species unique to Banff—a subspecies of longnose dace, a threeinch coldwater fish that has genetically adapted itself to the warm waters, and a snail that is found nowhere else.

Still, although some hardy tropical fish have done well in the shallow, densely vegetated marsh, where the warm water flows over an area the size of four football fields, hundreds of other strains have not survived. Nelson discovered no trace of such species as guppies and swordtails, which the Canadian Wildlife Service first noted in a 1968 survey. But if there are no dramatic changes in the sulphurous marsh, Nelson says he believes that the three established species there now will thrive. As a result, Canada’s premier national park, which celebrates its 100th anniversary this year, will continue to have an unexpected tourist attraction as it begins its second century.

-SUZANNE ZWARUN in Calgary.