ASA 127th Meeting M.I.T. 1994 June 6-10

5pUW21. In-situ target strength measurements of Antarctic zooplankton.

David A. Demer

Scripps Inst. of Oceanogr., Univ. of California at San Diego, La Jolla, CA 92038

Roger P. Hewitt

Southwest Fisheries Sci. Ctr., La Jolla, CA 92037

In situ measurements of target strength were made of krill (Euphausia superba) and salps (Salpa thompsoni) at 120 and 200 kHz. Concurrently, a 2-m Isaacs-Kidd underwater trawl was used to sample the zooplankton population; animal length, wet weight, and maturity stages were recorded. These data were combined to derive empirical models of TS versus length for both species. The individual target strength measurements were collected at 120 kHz with a split-beam echosounder and a single-target detection algorithm. Because the two transducers were essentially colocated, range bin and off-axis angles from the 120-kHz detections were used to extract the corresponding target strength from the 200-kHz single-beam data. Backscattering strengths of salps are shown to be higher at 200 than 120 kHz. Utilizing these scattering characteristics, signal separation methods are explored that would be useful in acoustic surveys of krill distribution and abundance. Data were collected as part of the United States Antarctic Marine Living Resources Program, near Elephant Island, Antarctica, during the Austral summer of 1994. [Work of D. A. Demer was supported by the Hertz Foundation.]