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

Abstract

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.

Factors Influencing Capture and Retention of Razorback Sucker in Light Traps

“…If the light source is intense enough, i.e., close enough to the larva, it may be sufficient to attract and retain even less phototactic life stages. If this is the case, it indicates that the use of brighter light sources may be more effective at attracting older and larger life stages of fish, a hypothesis also supported by LED light trap experiments reported elsewhere (de Vlaming 2019; de Vlaming and Bestgen, in press). However, Snyder and Meismer (1997) found no effect of light intensity on the capture of Razorback Sucker by light traps, except for juveniles, where a negative effect on capture was observed; it is possible that their findings were confounded by the use of differing light trap designs or their circular experimental arena compared with our linear one.…”

Laboratory and field evaluation of a new light‐emitting‐diode‐lit quatrefoil light trap for sampling fish early life stages

“…It is noteworthy that one LED trap captured 617 fish, 380 of which were Razorback Sucker, despite light failure prior to pulling the trap, which may be a conservative number due to the strong influence of light on larvae retention (de Vlaming and Bestgen 2020a). Experimental release and recapture of larval Razorback Sucker in a large floodplain wetland also supported our finding that LED traps captured more Razorback Sucker larvae than CL traps (de Vlaming and Bestgen 2020b). Overall, these collective results support a switch by field workers to LED light sources in traps.…”

“…This indicated that differences in light intensity between the new and old light sticks, due to the reduction in the amount of energy released in the chemiluminescent reaction over time, is the reason for the decline in capture probabilities and not the light type specifically. The belief that light intensity was the primary driver of capture rates was also supported by the laboratory choice experiment, where 5.5 times more Razorback Sucker larvae chose the brighter LED trap, and by field sampling in a large floodplain, where LED trap capture rates were 3.7 times higher than CL traps over a wide range of fish densities (de Vlaming and Bestgen 2020b). Additionally, the importance of light intensity also suggests that if use of CL traps is necessary, CL light sources should be replaced frequently to maximize light intensity during the sampling period.…”

“…The LED light source we used was specifically designed for use with quatrefoil light traps (e.g., de Vlaming and Bestgen 2020a, 2020b), modified from Killgore (1994). The LED light source circuit included a Super Bright Green 5‐mm LED (Adafruit), 47‐ohm through‐hole resistor, a 3.7 V, 2500‐mAh lithium‐ion polymer battery (Adafruit), and a USB 1.2 V LiIon/LiPoly charger (Adafruit).…”

“…Our goal was to design and test an original, lightweight, LED light source specifically for use with modified quatrefoil light traps used during Razorback Sucker larvae sampling. We included a light dissipation attachment as described in Floyd et al (1984b) and used green‐colored lights, which are attractive to fish (Kurien et al 1952; Marchetti et al 2004) and similar in color to typical CL traps successfully used in many field applications (de Vlaming and Bestgen 2020a, 2020b; M. T. Jones, personal observation)—we opted for a lightweight rechargeable lithium‐ion battery for portability. Investigations were done in both laboratory and field settings to provide comprehensive comparisons between CL‐ and LED‐lit light traps on capture and retention of early life stages of Razorback Sucker.…”