MANAGEMENT AND CONSERVATION OF BROOK TROUT IN WESTERN MARYLAND

Abstract

Widespread declines have been observed in the abundance, distribution, and size structure of Brook Trout for nearly 200 years. Although broadly distributed, Brook Trout are very sensitive to environmental disturbances, and populations continue to disappear. Environmental change further threatens the persistence of wild Brook Trout, and even currently secure populations may be at risk. Life history variation and population substructures further confound management, and their potential influences on population dynamics warrant further investigation.

The objectives of my dissertation were to characterize Brook Trout populations in western Maryland and use this information to forecast alternative futures. We used a large-scale mark-recapture survey (>3,000 marked fish), molecular tools, and simulation modeling to gain a comprehensive understanding of the structure and function of Brook Trout populations in western Maryland.

We found that rapid visual assessment was a valid technique (92% accuracy after training) for determining sex in Brook Trout. We found significant variability in individual growth rates (0-144 mm*y-1), with marked influences of year, sex, size, and stream. We also detected the presence of cryptic metapopulations occurring on a small spatial scale and in the absence of physical barriers to movement. Population substructures such as sex or lineage are easily overlooked, yet they may have measurable and potentially important differences in vital rates.

Simulation modeling under current and alternative conditions suggested that environmental stochasticity exerts a strong influence on the population dynamics of wild Brook Trout in western Maryland. Population dynamics were driven by pulse-driven recruitment that was weakly related to spawner abundance. Changes in adult survival, representative of a range of management scenarios, had a considerable impact on population resilience. Conversely, changes in the growth rates of Brook Trout resulted in small changes to population resilience. Enhanced adult survival resulted in a greater abundance of large fish. Collectively, these results suggest regulatory approaches may offer some utility in promoting population resilience while enhancing the quality of the fishery, but are likely insufficient to fully offset the impacts of predicted environmental changes.