Original ArticlesAre culvert assessment scores an indicator of Brook Trout Salvelinus fontinalis population fragmentation?

- Genetic differentiation is greater at sites with culverts than those without.
- Culvert assessment classifications and scores do not predict extent of fragmentation.
- Culvert openness ratio is a significant predictor of genetic differentiation.
- Evaluations of barriers using genetics is a useful tool for prioritizing restoration.

Fragmentation is a major threat to the integrity of stream ecosystems and maintaining connectivity is a primary goal for conservation to promote natural system functioning. In human dominated systems with extensive anthropogenic fragmentation, resource managers are faced with prioritizing restoration actions to provide the most cost-effective conservation strategies. Road crossings, particularly poorly designed culverts, limit fish passage and thus population connectivity and access to seasonally important resources. Culvert assessment protocols, such as the one developed by the North Atlantic Aquatic Connectivity Collaborative (NAACC), are useful tools for managers to evaluate culvert passability and prioritize restoration actions across broad spatial extents, however the justification of such protocols requires empirical field based investigations. In this study we collected Brook Trout genetic samples from 28 headwater streams, of which 17 were separated by a culverted road crossing and 11 were included as a comparison to natural genetic structuring. The objectives of this research were to 1) determine what effect culverts had on the genetics of Brook Trout populations, 2) evaluate the ability of the NAACC culvert assessment protocol to predict genetic patterns and 3) identify the culvert characteristics that best explained genetic variability. We found significant increases in genetic differentiation at sites with culverts compared to those without, but no differences in genetic diversity metrics. Although the NAACC classifications did not predict the extent of genetic differentiation, the openness ratio of culverts (cross sectional area/length) was significantly correlated, suggesting it may need to receive a higher weighting in assessment protocols. Our results highlight the necessity to match appropriate prioritization strategies with desired management objectives in order to design the most effective conservation actions.