Low Light as a Possible Impediment to River Herring Migration

摘要

Pipes and box culverts are economical alternatives to bridge construction over211u001esmall water bodies: however, low light levels inside these structures may prevent 211u001eadult river herring from passing through them on the way to historical spawning 211u001eareas upstream. The effects of pipes and culverts on herring migration behavior 211u001ewere investigated using gillnet sampling, acoustic observations, and experimental 211u001efield manipulations. Light measurements indicated that lighting was lowest in 211u001ecorrugated metal pipes of < 6' (1.8 m) diameter and was greatest at bridges that 211u001ewere at least 1 m (3.3 ft) off the water surface. No river herring were captured 211u001eduring gillnet sampling at pipe and box culvert sampling sites in 1998; yet these 211u001efish were captured at bridge control sites. The absence of herring indicates that 211u001epipes and culverts may have contributed to the extirpation of herring from the 211u001euppermost reaches of these streams; however, poor water quality may also be 211u001eresponsible. River herring on both the upstream and downstream ends of a box 211u001eculvert were sampled in 1999 with the gillnets. The authors' observations 211u001eindicated that some of the fish were able to negotiate this very long culvert and 211u001ethat they needed minimal lighting to do so. Morevoer, a higher percentage of fish 211u001emigrated through this structure at night than during the day.