Survival of different size-groups of the scallop, Mizuhopecten yessoensis (Jay), after transfer from collectors to the bottom

Abstract

Cultivation of the Japanese scallop, Mizuhopecten yessoensis (Jay), in Primorye Territory (Russia, Sea of Japan) involves collection of scallop spat, rearing them for 1 year in suspended collectors, and then seeding on the sea bottom where the scallops grow for 2 years to attain a commercial size of over 100 mm. Survival of juveniles after transfer to the bottom depends considerably on their size and environmental conditions in the area of cultivation. Well-aerated areas with sand or muddy sand bottoms, protected from heavy wave action, with almost stable high salinity, and with summer water temperatures not above 16–18°C were most favourable for scallop culture. Under these conditions, most juveniles with a shell height greater than 15–16 mm survived. There was a high mortality rate in seeded individuals during only a month after transfer. In less optimal environments of fine-grained sand or aleurite-muddy bottoms, only scallops which had an initial shell height greater than 19–20 mm survived. These molluscs showed a high survival rate in only 2–3 months after transfer when their shell heights exceeded 37 mm. On pebble-gravel-sand bottoms, only individuals larger than 22 mm survived. Observations on survival of young scallops with different shell heights in various areas allowed us to conclude that individuals with small shell height should not be planted under certain environmental conditions, or that sowing density should be increased here in order to optimize utilization of the scallop culture grounds.