Dealing with uncertainty when assessing fish passage through culvert road crossings

Area of Science:

• Ecology
• Environmental Science
• Conservation Biology

Background:

• Culvert road crossings often impede aquatic organism passage, hindering stream habitat restoration.
• Existing assessment criteria for culvert impassability vary and often focus on larger fish species.
• Small-bodied fishes face unique challenges with culvert passage, requiring tailored assessment methods.

Purpose of the Study:

• To evaluate how different criteria for assessing culvert impassability affect prioritization for remediation.
• To identify culverts for restoration benefiting imperiled small-bodied fishes in the Upper Coosa River system.
• To assess the sensitivity of prioritization outcomes to varying impassability criteria.

Main Methods:

• Assessed 256 road crossings using four alternative criteria sets within Bayesian belief networks.
• Scored culvert impassability based on thresholds of culvert characteristics (e.g., elevation, water velocity).
• Incorporated uncertainty regarding small-fish passage and estimated probabilities of impassability.

Main Results:

• Culvert prioritization varied significantly depending on the impassability criteria used.
• A subset of four culverts consistently ranked high for remediation across all criteria sets.
• Differences in prioritization highlight the impact of chosen assessment methods on management decisions.

Conclusions:

• Explicitly incorporating uncertainty into culvert assessment criteria is crucial for effective remediation decisions.
• Comparing outcomes from alternative criteria can identify key research needs to reduce management uncertainty.
• Tailored approaches are necessary to ensure culvert remediation benefits imperiled small-bodied fishes.