RELATIONS AMONG FISHERS, SNOW, AND MARTENS - DEVELOPMENT AND EVALUATION OF 2 HYPOTHESES

Literature about the fisher (Martes pennanti) contains the following c ontradictions: (I) the species is an old-growth specialist versus a fo rest generalist, and (2) it lives with marten (M. americana) with mini mal interaction versus densities of the two species are inversely rela ted. These contradictions beg the questions of what is fisher habitat and does habitat affect the interactions of the two Martes. These ques tions were examined by analyzing the distributions of fishers (n = 15, 549) and martens (n = 40,516) harvested in Maine, 1980-1987. This peri od was chosen because it had relatively stable pelt prices that were b elieved to result in harvests reflecting population occurrences. The s patial distribution of mean harvests of fisher and marten were compare d to each other, and to snowfall distribution and frequency throughout Maine, 1980-1987. Martens were common only in northwestern Maine and were associated with frequent (monthly X ($) over bar = 6.5) and deep (total monthly X ($) over bar greater than or equal to 48 cm) snowfall s, December-March. Fishers were rare in northwestern Maine but were co mmon throughout the rest of the state where snowfalls were less freque nt. We hypothesize that regular accumulations of deep snow reduce the fisher's fitness (via decreasing recruitment, survival, or both), resu lting in a low abundance in northwestern Maine. In addition, we hypoth esize that martens are rare in southern Maine due to competition from a dense fisher population. These hypotheses were evaluated by looking at patterns in age and recruitment ratios of fishers (n = 2,706) and m artens (n = 5,572) harvested in core and non-core habitats for each sp ecies, 1980-1984. We found low indices of fisher recruitment (P < 0.00 1) in the marten's core habitat consistent with the hypothesis that de ep and frequent snowfalls limit fishers. Few adult martens were harves ted (P < 0.001) in the core habitats of fisher, consistent with our hy pothesis that high fisher densities limit marten populations. Assuming our hypothesis on fisher-snow relations is true, and given that canop y closure affects snow accumulation, fisher habitats deserve more cons ideration in forest management in regions with frequent powder-snowfal ls, fragmented forests, or both. We acknowledge, however, that both of our hypotheses (i.e., snow Limits fisher and fisher limit marten) nee d direct testing because association does not prove causation.