Light Trap Effectiveness to Capture Razorback Sucker Larvae in a Large Floodplain Wetland

Light trap captures of larval Razorback Sucker Xyrauchen texanus are used to trigger flow releases from Flaming Gorge Reservoir, which inundate floodplain wetland nursery habitat in the Green River, Utah. However, because little is known about the efficacy of traps to capture or retain larvae under field‐relevant conditions, we conducted an exploratory study using releases of unmarked and marked (oxytetracycline hydrochloride) early life stages of Razorback Sucker (mesolarval life stage, hereafter called “larvae”) in the 53‐ha Leota‐10 wetland of the middle Green River. Batches of 10, 50, 250, or 1,000 larvae were released 3‐ or 10‐m from light traps. Light traps had either chemical light stick or LED light sources, and releases were made on two successive evenings to assess recapture proportions. Light traps recaptured larvae each night and at all release abundances in this large and open habitat. Recapture proportions (number recaptured per number released) for individual traps ranged from 0 to 0.68 (mean = 0.11) over the two release nights. Because recapture proportions were similar over all release abundances, light trap captures may be an index of larvae abundance. In addition, recapture proportions of larvae in traps (light sources combined) were not influenced by release distance. Nonsignificant tests for release distance and release abundance effects had low statistical power resulting from high sample variability and modest sample sizes, so additional experiments are required to confirm those results. The ANCOVA also indicated that traps with an LED light source had consistently higher recapture proportions than traps lit with chemical light sticks, in support of laboratory findings. Although additional experiments with greater replication are needed to better understand attraction distance, release abundance, and retention effects, light traps may be a useful tool to monitor presence and abundance of larvae. This information will aid management and conservation of endangered Razorback Sucker in the Colorado River basin.