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Longitudinal Differences in Brook Trout Density and Mean Length in Headwater Streams of Western Massachusetts

Brook trout (Salvelinus fontinalis) face many threats throughout their native range in the eastern United States including climate change, invasive species, and recreational angling. Understanding the habitat requirements and distribution of young of the year and adult brook trout in small headwater streams is essential for the conservation of the species. With this research, we sought to better understand the distribution pattern of young of the year, detect seasonal movement of adults before and during the spawning season, and determine if young of the year and adults preferentially inhabit stream reaches of different sizes. To explore these fishhabitat relationships, we electrofished 30 meter reaches with catchment areas ranging from 0.09 km to 4.90 km in the headwater systems of two western Massachusetts watersheds. Sampling was conducted during the spring and fall of 2014. We used generalized linear mixed models to evaluate young of the year density and linear density, adult density and linear density, and mean length of all fish sampled. The results for young of the year indicate that their distribution is quadratic or increases with stream size. We found no seasonal differences in adult densities. We also did not find a longitudinal difference in mean length. These results lead us to believe that the catchment sizes included in this study are equally important for brook trout persistence and should all be considered conservation priorities. This study demonstrated a need for additional research in the upper reaches of headwater streams since our models did not explain a significant proportion of the variability in the data. Additional landscape variables should be measured to better understand how brook trout population dynamics vary longitudinally in headwater streams and how the streams should be managed in the future. Introduction: Brook trout (Salvelinus fontinalis) are stream-dwelling fish native to the Eastern United States. Brook trout depend on cold, oxygenated water for suitable habitat and have a narrow thermal limit (10-19°C: Hillman et al. 1999), and thus are likely to be impacted negatively by increasing water temperatures associated with climate change. In addition to decreased habitat availability due to warming waters, the distributions of warmer water stream species such as smallmouth bass (Micropterus dolomieu), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss) are shifting upstream and putting additional pressure on native brook trout (EBTJV 2006). Populations of brook trout are declining over much of their native range with many isolated to the headwaters of stream systems (Hudy 2008). These isolated populations are particularly vulnerable to habitat degradation and changes in stream connectivity (Mollenhauer et al. 2013). It is thus important to understand how these populations are distributed throughout streams and how habitat use changes longitudinally. Although considerable research has