A growth profile for the rock scallop Hinnites multirugosus held at several depths off La Jolla,California

Juvenile Hinnites multirugosus were held in cages secured at 6 depths (maximum 120 m) to a buoyed line in the ocean 5 km off Scripps Institution of Oceanography for 95 days (August–November, 1977). The line was retrieved on December 2, and the scallops were measured, weighed and sacrificed for internal study. A second similar line, lowered at the same time as the first, was allowed to remain at the station for observation until later in 1978. Scallops at the shallowest depths (8, 15, and 30 m) displayed the most rapid growth, groups (n=10) averaging 19.3, 25.5 and 21.7 mm increases in shell diameter, respectively. These growth rates were comparable to the best results for scallops held in food-rich waters of Mission Bay, San Diego, California. Groups at the deeper levels (60, 90 and 120 m) grew by averages of 15.3, 8.5 and 7.8 mm, respectively. Growth was less than expected at 8 m, presumably due largely to competition for food and growing space by fouling organisms (barnacles, bryozoans, hydroids and colonial tunicates). Fouling was minimal at depths exceeding 30 m. The known vertical distribution of temperature and particulate organic matter in the ocean off La Jolla indicates that both influenced scallop growth in this study. A temperature range of 5 to 10 C° from the surface to a depth of 100 m is common to the area. Phytoplankton are generally concentrated in the upper 50 m.