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The squid Loligo opalescens lays its eggs in capsules attached to a flat sandy substrate. These capsules are usually clustered in so‐called egg beds. Earlier work in Monterey Bay, CA [Foote et al., J. Acoust. Soc. Am. 119, 844–856 (2006)] established the acoustic detectability of such egg beds. This work has now been extended in a new study performed in June 2006. An EdgeTech sidescan sonar was towed at nominal 5‐m height over the bottom. Measurements were made at 400 kHz, horizontal beamwidth 0.5 deg, along six parallel transects, with adjacent centerlines separated by 30 m. The swath width along each transect was 100 m. The transects were repeated on 10, 13, and 14 June. Data from areas where egg beds were densely concentrated, confirmed by drop video camera, have been excerpted. Comparisons of corresponding data, which are generally very strong, are quantified. The question is asked as to whether such sidescan sonar data can be used differentially to measure egg‐laying success or hatching over rather short periods of time. If so, this could be a useful tool both in ecological studies and for management purposes. [Work supported by NURP.]

Publisher pdf: http://dx.doi.org/10.1121/1.2149840. Journal home page: http://scitation.aip.org/jasa/ The squid Loligo opalescens is a key species in the nearshore pelagic community of California, supporting the most valuable state marine fishery, yet the stock biomass is unknown. In southern Monterey Bay, extensive beds occur on a flat, sandy bottom, water depths 20–60 m, thus sidescan sonar is a prima-facie candidate for use in rapid, synoptic, and noninvasive surveying. The present study describes development of an acoustic method to detect, identify, and quantify squid egg beds by means of high-frequency sidescan-sonar imagery. Verification of the method has been undertaken with a video camera carried on a remotely operated vehicle. It has been established that sidescan sonar images can be used to predict the presence or absence of squid egg beds. The lower size limit of detectability of an isolated egg bed is about 0.5 m with a 400-kHz sidescan sonar used with a 50-m range when towed at 3 knots. It is possible to estimate the abundance of eggs in a region of interest by computing the cumulative area covered by the egg beds according to the sidescan sonar image. In a selected quadrat one arc second on each side, the estimated number of eggs was 36.5 million.

Clusters of gelatinous egg capsules, known as mops or beds, of the market squid (Loligo opalescens) were mapped in a shallow‐water, sandy habitat of Monterey Bay, California. The benthic egg clusters were imaged using an EdgeTech 272‐TD dual‐frequency sidescan sonar towed from R/V MacGinitie, an 8‐m‐long survey vessel, with data recorded on a Triton Elics International Isis digital data acquisition system. Verification of target identity was accomplished independently by video photography from a remotely operated vehicle. The survey area included a 4‐km stretch of sandy seafloor between Lover’s Point and Cannery Row in Monterey at depths of 15–30 m. The study area had previously been mapped using the RESON SeaBat 8101 240‐kHz multibeam sonar. Resulting high‐resolution bathymetric data, with 1‐m resolution, were used during the survey planning and execution. Squid egg clusters were clearly visible in the very‐high‐resolution, 400‐kHz backscatter imagery, with pixel size 10–20 cm, recorded from the towed si...