The Influence of Road Crossings on Fish Movement in Ouachita Mountain Streams

Landrum, C. and C. J. Gagen, Fisheries and Wildlife Program, Arkansas Tech University, Russellville, AR 72801

Standage, R. W., U.S. Department of Agriculture Ouachita National Forest, Hot Springs, AR 71902

Low-water bridges are common in forested upland ecosystems. This study was initiated to measure the influence of road crossings on fish movement and assess the impact of the crossings on fish communities. We established three, sample sites in each of six upland tributaries of the Ouachita River, Arkansas. Three of the tributaries had crossings modified in an attempt to improve fish passage. The three sample sites included a 50-m reach upstream of a low-water bridge, another 50-m reach downstream of the bridge, and a 50-m reference reach. The low-water bridge was within a non-sampled 50-m reach between the upstream and downstream sampled reaches. Similarly, a 50-m reach without a low-water bridge, was not sampled between the downstream and reference reaches. We captured fish by electrofishing and marked them differentially by reach with a sub-cutaneous injection of a biologically compatible fluorescent dye three times in the spring and three times during the summer. Fish were less than half as likely to move 50 m across reaches with low-water bridges compared to 50-m reaches without low-water bridges. Fish moved upstream and downstream equally between reaches not separated by low-water bridges, but were twice as likely to move downstream, rather than upstream, between reaches separated by low-water bridges. Average species richness was higher for fish communities downstream of the low-water bridges compared to upstream (12.5 versus 6.3) indicating that the reduced movement could affect community structure. Two low-water bridges back-filled with rip-rap to eliminate the plunge pools below the aprons were the only ones allowing upstream fish passage. These preliminary findings suggest that engineering design could lessen the impact of road-crossings on the structure of fish communities in streams.

Copyright © 1999
Texas Chapter of the American Fisheries Society
Last modified: 01/07/09 06:45:17 AM