Behavioral Responses of Rainbow Smelt to in situ Strobe Lights

Abstract

We conducted in situ testing of strobe lights as a potential fish deterrent by examining avoidance and acclimation behaviors of rainbow smelt Osmerus mordax in Lake Oahe, South Dakota. Split‐beam hydroacoustics were used to assess the effectiveness of the deterrent system by comparing proximal densities of rainbow smelt before and after the device was activated. In summer 2005, strobe lights successfully repelled rainbow smelt to a minimum horizontal distance of 21 m at both 1 h and 4 h postactivation; the model AGL‐FH 920 flashhead produced a light intensity of 6,585 lumens per flash. Similarly in 2004, a model AGL‐FH 901 flashhead, which produced a light intensity of 2,634 lumens per flash, repelled rainbow smelt to a horizontal distance of 15 m. A comparison of strata 10 m above and below the strobe light system showed that rainbow smelt were vertically displaced to approximately 6 m. We conclude that strobe lights elicit behavioral avoidance by rainbow smelt and may provide an effective means for reducing entrainment losses through Oahe Dam.

Avoidance of strobe lights by zooplankton

“…Although it is unclear why some fishes are attracted to strobe lights, it has been hypothesized that strobe lights could potentially concentrate prey and/or increase feeding efficiency for visual-feeding fish (Johnson et al 2005). In Hamel et al (2008), rainbow smelt were deterred 15 m away from the strobe light in tests conducted in 2004. However, hydroacoustic estimates taken at distances farther than 15 m showed similar rainbow smelt densities as control estimates and may have increased in abundance after sustained operation (Hamel et al 2008).…”

“…In Hamel et al (2008), rainbow smelt were deterred 15 m away from the strobe light in tests conducted in 2004. However, hydroacoustic estimates taken at distances farther than 15 m showed similar rainbow smelt densities as control estimates and may have increased in abundance after sustained operation (Hamel et al 2008). Because cyclopoid and calanoid copepods and daphnid densities were reduced near the strobe lights in this study, it is unlikely that the attraction of fish to strobe lights found in other studies is due to concentration of zooplankton.…”

“…comm.). An anchored boat, equipped with a hydraulic winch, was used to lower the strobe light to a depth of 25 m. This depth corresponds to the thermocline and is the approximate proposed depth for installation of strobe lights near the Lake Oahe dam intake structures (Hamel et al 2008). …”

“…The first of the 3 sites along each transect was located <1 m from the strobe light; the second site was located approximately 15 m away (at the outer peripheral region of the AGL-FH 901 strobe light; Hamel et al 2008); and the third site was located at 100 m, beyond any observable light. Zooplankton were collected using a conical-shaped closing net (0.5 m dia), constructed of 150 µm mesh, at depths of 0-10 m (upper), 10-20 m (middle) and 20-30 m (lower) at the 3 distances along each transect.…”

“…Strobe lights have recently been evaluated as a possible solution for reducing entrainment of rainbow smelt (Osmerus mordax; Hamel et al 2008). While strobe lights were successful at deterring rainbow smelt, our purpose in this study was to elucidate the effects strobe lights have on zooplankton distributions and local abundance and discuss the implications artificial light may have on the feeding ecology of primary and secondary consumers.…”