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December 1993 Notes 401 Individual trap sets baited with dog food (n = 82) never exceeded capture rates higher than 0.1 razorback sucker larvae per hour and traps baited with cyalume light sticks (n = 92) yielded a max- imum of only 0.2 per hour. Sucker larvae ap- peared to be primarily attracted to white lights with intensities exceeding 2,100 lux. Twelve-watt lights yielded averages of 2.8 (n = 15) and 29.8 larvae per hour (n = 11), and 55-watt halogen bulbs produced 6.0 (n = 13) and 14.5 larvae per hour (n = 13) in Yuma Cove and Arizona Bay, respectively. Average total length of razorback sucker larvae in a subsample (n = 48) was 11.3 mm, with a range of 10.5 to 12.7 mm (SD = 0.5). Larval fish traps equipped with 12- and 55- watt white lights were more effective in capturing razorback sucker larvae than traps using cyalume light or bait. These results supported earlier work (Kurien et al., 1952) indicating that white light may be more effective in attracting small fish than colored light. The data suggest that capture rates increased with light intensity, however, there ap- pears to be some evidence that Odonate nymphs and possibly razorback sucker larvae may avoid light intensities exceeding 4,500 lux. Capture rates of larval razorback did increase (2.75-5.98 larvae/h) in Yuma Cove by using 55- watt lights. However, radiant conditions were inferior to those in Arizona Bay. Yuma Cove was totally isolated and highly productive. Dense swarms of zooplankton and macroinvertebrates were attracted to the lights and obscured light intensities. Twelve-watt lights proved more effective than brighter 55-watt halogen lights for capturing lar- val suckers (48.27-29.08 larvae/h) and Odonate nymphs (3.03-0.11 nymps/h) in the less pro- ductive waters of Arizona Bay. Many larvae were attracted to the brighter halogen lights, but from observations of larvae observed around the traps compared to capture counts, we estimate that in some cases fewer than 20% actually entered the traps. Radiant energy measurements of the 12- and 55-watt (2,100-4,500 lux) bulbs do exceed light intensities reported to affect some fish species. We suspect that larval suckers are attracted to light intensities greater than 4,500 lux, but they may avoid entering the traps at such intensities. Under more turbid water conditions larvae many be ef- fectively attracted into the traps. Fish avoidance of high light intensity has been reported by a number of authors (Wolf and Zer- rahn-Wolf,1936; Jones, 19 56; Woodhead, 1956). TABLE 1-Capture rates of razorback sucker larvae and odonate nymphs using larval fish traps in Yuma Cove and Arizona Bay, Lake Mohave, Arizona-Ne- vada, from 19 February to 20 April 1992. n Effort (h) Larvae/h Nymphs/h Yuma Cove Dog food 19 81.82 0.00 0.45 Dog food, 31 251.15 0.00 0.20 Cyalume 25 128.70 0.03 8.99 Cyalume, 32 259.38 0.00 10.70 12 watt 15 20.37 2.75 25.35 55 watt 13 16.43 5.98 14.27 Arizona Bay Dog food 15 69.38 0.06 0.00 Dog food, 17 181.00 0.00 0.01 Cyalume 15 69.13 0.20 0.07 Cyalume, 20 205.52 0.00 0.00 12 watt 11 17.83 29.78 3.03 55 watt 13 26.08 14.48 0.11 , Traps set at depths greater than 1 m Minnows (Phoxinus phoxinus) exhibited limited phototactic response to light above a certain in- tensity (0.2-0.002 lux). Sunfish (Lepomis sp.) have been reported to suffer "injurious effect (eye flick- ering) of high intensities (1,000 lux)" (Wolf and Zerrahn-Wolf, 1936) while other species, such as walleye larvae (Stizostedion vitreum), exhibited phototactic response to maximum light intensities of 7,800 lux (Bulkowski and Meade, 1983). The use of gel-cell batteries allows a greater choice of light intensity and duration than light traps used in other studies (Paulson and Espi- nosa, 1975; Faber, 1981; Muth and Haynes, 1984; Gregory and Powles, 1985; Dewey and Jennings, 1992). Greater flexibility will permit further light intensity refinement for phototactic species less sensitive to light or those found in more turbid waters conditions. Although the evidence of light intensity avoidance is not conclusive, we urge cau- tion in the use of high intensity light and rec- ommend additional research to determine optimal light intensities. Although light-trap collections, like spotlight collections, do not represent quantitative esti- mates of larval densities, they do provide an index of relative larval abundance. Trapping, unlike netting, is not biased by personal skill and pro- vides a method of expanding sampling effort. This research was funded by the Bureau of Reclamation, Lower Colorado Region, Boulder City, Nevada. Permits were granted by the Ar-