Siberian fur trade to overhunting. Instead of one sable pelt, the following was accepted as its equivalent: one fox, glutton (relative of the marten), or otter pelt; two blue-fox pelts; sixteen polar-fox pelts; or one hundred squirrel pelts. The Russian government decided the amount of other pelts that were equivalent to the sable pelt. Within forty years, almost all Siberian natives were forced into paying fur tribute to the Russians. Russian traders, hunters, and explorers reached the Pacific coastline by 1650 and were collecting fur tribute from most natives along the coast. Beyond the yasuk, the Russians had two principal ways of obtaining
American marten of study. Juvenile survival rates were lower, ranging from 0.26 to 0.50. In Newfoundland, annual adult survival was 0.83. Survival of juveniles from October to April was 0.76 in a protected population, but 0.51 in areas open to snaring and trapping. In western Quebec, natural mortality rates were higher in clearcut areas than in unlogged areas. American marten are vulnerable to predation from raptors and other carnivores. The threat of predation may be an important factor shaping American marten habitat preferences, a hypothesis inferred from their avoidance of open areas and from behavioral observations of the European pine marten ("Martes