COMPARISON OF BROOK TROUT REPRODUCTIVE SUCCESS AND RECRUITMENT IN AN ACIDIC ADIRONDACK LAKE FOLLOWING WHOLE LAKE LIMING AND WATERSHED LIMING

Limestone applications to the catchment of one tributary to Woods Lake were highly effective in reducing stream acidity and stabilizing seas onal fluctuations in pH. The resulting improvement in stream water qua lity also led to a dramatic shift in reproductive strategy of the Wood s Lake brook trout population. Prior to catchment liming, brook trout in Woods Lake were restricted to spawning on poor quality near shore s ubstrate with limited ground water seepage. Reproductive success was l imited by high mortality of eggs and larvae and recruitment from in la ke spawning was not successful. Spawning brook trout did not utilize t he tributary for spawning prior to watershed liming. Mitigation of aci dity in the tributary, by catchment liming, effectively extended the s pawning habitat available to the Woods Lake brook trout population and one year following treatment brook trout spawned successfully in the tributary for the first time in 6 years of observation. Significant re cruitment of young trout into the lake population occurred from 1991 t hrough 1993, although the absolute number of fish captured was relativ ely small. In the fall of 1993, four year classes of naturally spawned brook trout were present in the lake. Although reproductive success w as enhanced by improving tributary spawning habitat in the Woods Lake basin, self maintenance of the population may be limited by low recrui tment rates of young trout, due to high levels of summer mortality res ulting from predation. Mitigation of this constraint would require sub stantially higher levels of fry production than were observed in Woods Lake and/or enhanced refugia for young trout. The results of this exp eriment suggest that re-establishment of tributary spawning population s of brook trout may be possible, with future reductions in acidic dep osition, in acidic Adirondack lakes with limited in-lake spawning habi tat.