Growth Rate of the Bivalve Nuttallia olivacea Measured by Marking-recapture and Caging

Abstract

The growth rate of the bivalve Nuttallia olivacea in the field was estimated by the marking-recapture and caging methods in a tidal flat at the mouth of the Natori River, Miyagi Prefecture. Individuals with a shell length of 9-20 mm were marked, returned to the tidal flat, and recaptured monthly for measurement of their size and weight. Furthermore, nylon cages filled with sand, into which bivalves 9-20 mm in shell length had been put, were buried in the flat. The size and weight of these bivalves were similarly measured. No significant difference between the two methods was detected by T-analysis of the estimated growth rate values. However, the recapture rate of marked individuals in the marking-recapture trials became lower 3 months after initial release, so that precise estimation became difficult with time. Daily increments in shell length and weight as well as the rate of growth were largest in summer (August to September), i.e., 110μm/day, 16.0 mg/day, and 1.63%/day respectively, and smallest in winter (February to April), i.e., 4.7μm/day, 2.9 mg /day and 0.1%/day, respectively. Water temperature varied from 5°C in February to 27°C in August. The annual growth in terms of shell length and weight was 13.49 (±2.44) mm and 3.14 (±0.89) g from June, 1995, to June, 1996, and 12.14 (±2.67) mm and 2.84 (±0.67) g from September, 1995, to September, 1996.