Effects of Road Crossings in Headwater Streams On Fish Movement Investigated With Radio Frequency Identification

Certain types of road crossings appear to hinder fish movement potentially fragmenting aquatic ecosystems. We studied the impacts of road crossings on fish movement in the Ouachita Mountains by marking fish with 12 mm, half-duplex, radio frequency identification (RFID) tags. We monitored fish movements in two streams with road crossings and two reference streams without road crossings using RFID detection stations composed of paired, swim-through antennas. The antenna arrays, composed of one antenna upstream of the road crossing or reference reach and another downstream, documented fish passage timing and direction. We selected half-duplex RFID tags, rather than the more common full-duplex tags, to take advantage of relatively large and inexpensive stream-spanning antennas that did not disrupt the natural habitat. The smaller 12 mm half duplex tags permitted study of fish as small as 85 mm but presented challenges in tag detection. We improved tag detection by designing antennas in a crossover pattern, dividing the stream into smaller cells. Preliminary results based on detections of >350 fish and ~90 passage events indicate higher fish passage rates on reference streams than respective culverted streams and higher passage rates by smallmouth bass and northern hogsuckers than other sunfish and minnows.