Movement and orientation of the Japanese scallop Patinopecten yessoensis (Jay) in response to water flow

摘要

This study examined the behavior of the Japanese scallop Patinopecten yessoensis (mean shell height = 56.8 mm) considering its movement and orientation in response to water flow under laboratory conditions. The behavior from initial movement to recessing was classified as follows: (1) swimming, (2) spinning on the longitudinal axis of the shell for orientation, and (3) coating itself with sand in a depression it made while recessing. In this process, 33% to 78% of the scallops swam downstream in flow velocities of 5-20 cm/s, but 38% of them were dislodged by a flow of 30 cm/s before they could recess. Recessed scallops tended to orient themselves with the ventral edge facing upstream in velocities of 5-10 cm/s. They tended to avoid directing the posterior edge upstream in a flow of 20 cm/s, although they opposed the flow with the dorsal edge in a flow of 30 cm/s. It was concluded that swimming downstream provides an efficient way for movement, and that the orientation behavior to flow is to optimize filtration and to avoid flow dislodgement. Therefore, cultivators of P. yessoensis should release the spat on beds where the flow velocity over the bottom does not exceed 10 cm/s frequently.