Growth advantages of ear hanging compared to cage culture for sea scallops, Placopecten magellanicus

Abstract

A study of field growth in sea scallops, Placopecten magellanicus, was conducted to establish possible advantages of ear hanging over cage rearing for suspended culture. Several hundred juvenile scallops (mean shell height of 44.3 mm) were allocated to both Nortene culture cages and ear-hanging arrays distributed at several depths in a shallow (7 m) study site in Lunenburg Bay, Nova Scotia. To account for growth variation, water quality data (e.g. temperature, salinity, current speed and chlorophyll- a) were collected hourly by in situ instruments moored at 1 m above the bottom, and direct water sampling was conducted biweekly. Growth rates of shell and soft tissue were calculated over several periods during the 5-month-long study. Culture method and height above bottom were both important to tissue growth, but their influence was neither consistent with time nor tissue type. Whenever culture technique was a significant effect, however, we found that ear-hung scallops grew faster than those enclosed in 6-mm-mesh plastic cages. In particular, adductor muscles of caged scallops grew by 45% over the study, whereas ear-hung scallops grew by 94%, although faster growth of ear-hung scallops was not apparent at all times. Growth differentials in soft tissues as a result of culture method were most apparent over the winter, when caged scallops had minimal growth (muscle tissue) or lost biomass (remaining soft tissue) at a greater rate than ear-hung scallops. Mortality of scallops in cages and ear-hung arrays was negligible. Although factors such as fouling may be problematic in ear-hung scallops, the growth advantages of this method coupled with its favourable economic stance in terms of gear and labour costs suggest it as an advantageous culture option.