チョウセンハマグリの生態について

Abstract

There are excellent harvesting grounds of “Chosen-hamaguri”, Meretrix lamarckii, along the open coast of Miyazaki Prefecture. Shells of this clam are used to make the white “stones” used in the popular Japanese game of “Go”, and the meat is greatly desired as food in the district. A study was made during 1903-1955 on some aspects of the biology of this clam, viz. habitat, spawning season, growth, movement and others. The results are summarized as follows: 1) This clam prefers the ocean water and is found on the sandy bottom in the water depths ranging from low tide mark down to 10 meters or more. 2) In the waters off Hyuga City, the spawning takes place between late July and late September. 3) The growth was estimated by Petersen's methed with the following results: at the age of one year, 0.66±0.03cm. in shell length, at two years, 3.43±0.07cm.; and at three years, 5.07±0.07cm. About 9.8cm. is the maximum shell length usually encountered in this district. 4) Marking experiment was conducted for the purposes of clarifying the local movement of the clam and verifying the above-mentioned estimate of growth. As the mark, several spots were engraved with the electric drill on the surface of one of the shells of each clam. The number of these spots, in combination with whether they were engraved on the right or left shell, was to denote the size of the clam at the time of marking. 14912 clams were marked by this method and released on May 15-23 and November 7-9 in 1953, and 294 of them were recaptured until February, 1955. The result of this experiment indicates that the clam scatters, with the increase in age, toward off-shore and also northward along, the coast. It was also shown that the foregoing estimate of growth was appropriate. 5) The relation between length and weight of shell was examined on the materials collected from two areas, off Hyuga City and Kitauramura, and the results for the two samples, were compared, as shown in Fig. 6. 6) The shell of this clam shows on the umbonal region a pattern called the “umbonal mark” which consists of two short radial lines of dark colour (Fig. 7). This pattern is characteristic of this clam, and is not found in Meretrix meretrix lusoria.