Lidar profiles of fish schools.

A lidar system was used in a seawater tank to measure the average diffuse reflectivity of live sardines. Diffuse reflectivity was measured to be 10 % for a copolarized laser return and 3 % for a cross-polarized return. We used these calibration measurements to infer the density of sardines in areas of the Southern California Bight from vertical profiles obtained with the lidar mounted on a ship. Within schools densities up to ~0.01 kg m-3 were observed. During hourly survey periods total habitat densities up to ~2 x10-3 kg m-2 were observed.