Production of Pacific oysters,Crassostrea gigasThunberg, from wild‐caught and hatchery‐produced seed grown at several densities on oyster shells

摘要

Abstract.Production of Pacific oysters was studied under pilot‐scale conditions in Baynes Sound, British Columbia, using common bottom culture strategies. Four seeding treatments, each with a different seed per cultch density were cultured: wild‐caught seed 5mm in shell height at 10 seed per cultch piece and hatchery produced seed 1‐2 mm in shell height at densities of 11, 40 and 105 per cultch piece. The cultch material for all treatments was Pacific oyster shell. All seed was reared for approximately 1 year in a seed nursery located at the 2.2‐m tidal level then transferred to a 1‐m tidal level grow‐out plot until harvest 4 years later in May 1988, Clusters of large numbers of oysters were separated and evenly distributed within the plots when the oysters attained a shell height of 60‐100 mm. During the first year, growth was slow and mortalities were relatively high. All treatments produced oysters of similar size at harvest. The proportion surviving at harvest was substantially higher for the wild oysters which were initially larger at time of planting. Within the hatchery treatments proportional survival per cultch piece was inversely related to initial density on the shell; however, total production per cultch piece was positively related to initial density. Most efficient use of seed is attained at lower densities per shell; however, most efficient use of cultch and effort to handle cultch is attained at h