Acoustic mapping of squid egg clusters and their bottom habitat in Monterey Bay, California

Abstract

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 sidescan sonar. The concentration of egg clusters was greatest along a sloping feature believed to be a submarine fault. Egg mops with diameter as small as 0.5 m were distinguishable. [Support by Sea Grant is acknowledged.]