Effects of Moonlight and Daylight on Hydroacoustic Estimates of Pelagic Fish Abundance
Originally published by the American Fisheries Society.
Note: This article appears in the Transactions of the American Fisheries Society and has been posted here with permission from the publisher.
To determine how moonlight and daylight affect hydroacoustic estimates of fish abundance, we used a dual-beam transducer and echo integration to survey pelagic fish (primarily Bonneville ciscoes Prosopium gemmifer) in Bear Lake, Utah and Idaho. During the new moon, the fish were dispersed (not schooling) below the thermocline, chiefly at the depths of 10–20 m. At full moon, they were dispersed but much closer to the bottom, where they were difficult to detect. Acoustic estimates offish density and biomass during full moons were approximately 50% of values derived during new moons. A diel survey during a new moon indicated that fish were widely dispersed in the water column at night, but formed schools at dawn. Our study indicated that light conditions must be standardized to insure consistent and comparable population estimates of some pelagic fishes.
Luecke, C. and W.A. Wurtsbaugh. 1993. Effects of moon and daylight on hydroacoustic estimates of pelagic fish abundance. Trans. Am. Fish. Soc. 122: 112-120.