Dealing With Uncertainty When Assessing Fish Passage Through Culvert Road Crossings

Abstract

Assessing the passage of aquatic organisms through culvert road crossings has become increasingly common in efforts to restore stream habitat. Several federal and state agencies and local stakeholders have adopted assessment approaches based on literature-derived criteria for culvert impassability. However, criteria differ and are typically specific to larger-bodied fishes. In an analysis to prioritize culverts for remediation to benefit imperiled, small-bodied fishes in the Upper Coosa River system in the southeastern United States, we assessed the sensitivity of prioritization to the use of differing but plausible criteria for culvert impassability. Using measurements at 256 road crossings, we assessed culvert impassability using four alternative criteria sets represented in Bayesian belief networks. Two criteria sets scored culverts as either passable or impassable based on alternative thresholds of culvert characteristics (outlet elevation, baseflow water velocity). Two additional criteria sets incorporated uncertainty concerning ability of small-bodied fishes to pass through culverts and estimated a probability of culvert impassability. To prioritize culverts for remediation, we combined estimated culvert impassability with culvert position in the stream network relative to other barriers to compute prospective gain in connected stream habitat for the target fish species. Although four culverts ranked highly for remediation regardless of which criteria were used to assess impassability, other culverts differed widely in priority depending on criteria. Our results emphasize the value of explicitly incorporating uncertainty into criteria underlying remediation decisions. Comparing outcomes among alternative, plausible criteria may also help to identify research most needed to narrow management uncertainty.

Assessing upstream fish passage connectivity with network analysis

“…By recognizing and accounting for uncertainty, we have provided decision makers with additional information not captured by cost-effectiveness alone (Anderson et al 2012, Rudnick et al 2012. For instance, given two alternatives with similar levels of HCIU, the alternative with less uncertainty may be preferable.…”

“…Because the focus of this paper is upstream habitat connectivity, we only applied upstream passage rates, and downstream passage is neglected. In other words, we examined diadromous life history whereby a species is migrating upstream from the mouth of the basin (Cote et al 2009, and we implicitly assumed that if a fish can move upstream that downstream loss is minimal relative to upstream movement (Anderson et al 2012). We also assumed that habitat is utilized equally per unit area or stream length.…”

“…Furthermore, passage rates vary with species, life history stage, environmental variability, direction of passage, temperature, discharge, and numerous other factors. A variety of techniques can be applied to assess passability, including: empirical observation (e.g., filming, hydroacoustics, telemetry), indirect surveys around a barrier (e.g., abundance and occupancy methods; Norman et al 2009), genetic surveys, rule-based models coupling fish physiology and hydrodynamics (e.g., Coffman 2005, also FishXing;Furniss et al 2006), statistical models (e.g., Bayesian Belief Networks; Andersen 2010, Anderson et al 2012), individual-based models (e.g., Goodwin et al 2006), and expert opinion (e.g., scoring systems; WDFW 2000, Martin and Apse 2011). Kemp and O'Hanley (2010) provide a thorough review of these methods, as well as their strengths and limitations.…”

Predicting road culvert passability for migratory fishes

“…We chose three water velocity thresholds, 0.4, 0.7 and 1.0 m s À1 , to represent a range of swimming abilities. The 0.4 m s À1 threshold was aimed at identifying road culverts that were impassable in an upstream direction under base or higher flow conditions for young or weak swimming migratory fish species such as the river darter (Percina shumardi) (Warren & Pardew, 1998;Anderson et al, 2012). The 0.7 m s À1 threshold was aimed at identifying the occurrence of road culverts that would be impassable by migratory species with moderate swimming speeds, such as adult northern pike (Esox Lucius), walleye (Sander vitreus) or white suckers (Catostomus commersonii) that are moderately strong swimmers (Peake 2008).…”

Substrate roughening improves swimming performance in two small-bodied riverine fishes: implications for culvert remediation and design

“…Design criteria of culverts have been revised in recent years to improve fish passage (Barnard et al ., 2015; Van der Ree et al ., 2015; Duguay and Lacey, 2016) but many existing structures require remediation (Andersen et al ., 2012). While there are numerous remediation approaches, the effectiveness of culvert roughening (i.e.…”