Assessment of Brook Trout Passage Through Ambiguous Culvert Barriers in Pennsylvania Headwater Streams

Abstract

Habitat fragmentation driven by human activity is a common threat to aquatic organisms. Road culverts in particular can isolate fish populations and reduce genetic diversity by preventing access to upstream spawning habitat. The prioritization process for removing culverts and restoring connectivity includes an assessment of passibility. Culverts often receive scores that categorize them as partial barriers, known as “Reduced AOP” culverts, however detailed assessment of passibility on gray culverts is lacking. To fill this research gap, we used stationary PIT-tag readers to investigate brook trout passage through two No AOP culverts, one Reduced AOP culvert, and a reference stream lacking a culvert for 16 months in Little Bear Creek of Lycoming Co., PA. Results indicate significant differences in upstream movement rates among culvert sites. The rate of upstream passage was five times greater through the metal corrugated culvert than the reference stream. In contrast, relatively little upstream movement occurred through the two box culverts (up to 13 times less passage than the reference), indicating drastic passage differences in culverts receiving similar passibility scores. Our study implies that more nuanced culvert classifications may be needed to accurately reflect fish passage