ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

2pAO3. Small scale spatial structure in zooplankton from high-frequency acoustical measurements.

D. V. Holliday

Tracor Appl. Sciences, Anal. and Appl. Res. Div., 9150 Chesapeake Dr., San Diego, CA 92123

Volume backscattering was measured at multiple discrete depths at frequencies of 0.165 and 1.1 MHz from a mooring on the shelf-slope break at the northern edge of the San Pedro basin near Los Angeles, CA. Attempts to understand temporal variability and vertical structure in the data from the mooring led us to make additional measurements along an onshore--offshore transect at this location at frequencies of 0.265, 1.1, 1.8, and 3.0 MHz. These measurements, when processed with an inverse algorithm to determine plankton size and abundance, revealed both an onshore--offshore trend and small scale structure in this environment. Results of sampling the same environment with a multiple opening--closing net sensor system (MOCNESS) are consistent with the acoustical measurements, but at the same time highlight the difficulty of sampling a heterogeneous spatial distribution with a net system. [Work supported by ONR, NSF, and Tracor Applied Sciences.]