Rubber ramp and spat rope did not facilitate upstream passage of a galaxiid through a perched culvert

Abstract

Poorly installed or undersized culverts at road crossings are one of the most frequently encountered barriers to fish movements, especially for small-bodied fish species. Although replacement with more ‘fish friendly’ culvert designs is the preferred solution, at many sites remediation will be required in the short to medium term. Consequently, there is a need for effective evidence-based fish passage solutions that can be deployed at scale. This study examined the passage efficiency of juvenile īnanga (Galaxias maculatus) past a perched culvert fitted with spat ropes and a flexible rubber ramp. Only four fish (0.79%) successfully passed the ramp, and no fish successfully passed the whole culvert by the conclusion of the trial. Deployment of flexible rubber ramps to remediate fish passage at perched culverts has recently become common practice in several regions of New Zealand, despite the absence of any evidence base to support their use. This study provides a strong preliminary indication that flexible rubber ramps are an ineffective fish passage solution for remediating perched culverts for non-climbing fishes. To overcome low head-migration barriers, there are alternative evidence-based fish ramp designs, which practitioners can have considerably greater confidence in for achieving restoration goals.