CURRENT STATUS OF THE INTRODUCED BEAVER (CASTOR-CANADENSIS) POPULATION IN TIERRA-DEL-FUEGO, ARGENTINA

The North American beaver (Castor canadensis) was introduced in Tierra del Fuego 40-years ago. The availability of suitable feeding and lodging sites coupled with the lack of natural predators or competitors favored rapid population growth and range expansion. In 1981, the Tierra del Fuego government authorized hunting to control the increasing beaver population. This study was conducted to investigate the current status of beaver populations, and to analyze modifications to the forest ecosystem of Tierra del Fuego, induced by beavers. Currently, beavers have colonized not only Isla Grande, but also other islands of the complex Magallanico Archipelago. Approximate densities are about 0.2-5.8 beaver colony sites per km, geographical range is about 20 000 km2 in the Argentine sector. Beaver colonies along Fueguian streams show occupancy patterns that are related to the basin geomorphology. This study indicates that beaver activities are modifying the forest ecosystem through: (i) Expansion of wetland areas; (ii) elevation of the watertable; and (iii) accumulation of organic material that modifies the biochemical composition of water, sediment and soil of riparian areas.