Laboratory Experiments to Determine Effectiveness of Light Traps to Detect Razorback Sucker Larvae

Authors: Catherine Devlaming, Kevin Bestgen

Year: 2018

Abstract

Detection of endangered Razorback Sucker Xyrauchen texanus larvae by light traps is used to prompt flow releases to inundate Green River floodplain wetlands, habitat which may increase survival of those early life stages. However, little is known about the efficacy of light traps to capture or retain larvae. In the laboratory, we investigated effects of light trap set time, release distance from trap, light presence, and turbidity on capture and retention rates of four early life stages of Razorback Sucker. Mean capture rates of protolarvae prior to the development of a swim bladder (7-9 mm total length [TL]) was 40% (28-55%) over the various treatment effects, but rose to 76% (73-80%) after protolarvae formed a swim bladder (9-10 mm TL). Mesolarvae (11-17 mm TL), the most commonly captured life stage in field sampling, had similar mean capture rates as later protolarvae at 86% (82-90%). Capture rates of metalarval (mean = 42%, range 21-63%; 15-24 mm TL) and juvenile (mean = 24%, range 20-28%; 22-37 mm TL) life stages were lower. Retention rates were generally > 75% and increased to 97% for juveniles. The relationship between set time and distances of 1-5 m on capture indicated longer set times positively influenced capture rates while distance had little effect. Light traps may be a useful gear to detect first presence of Razorback Sucker larvae in riverine backwaters each spring, timing of which is used to begin high flow releases from Flaming Gorge Dam to inundate Green River, Utah, floodplain wetlands.