大阪湾におけるガザミの成長

Abstract

To estimate the growth of swimming crabs Portunus (Portunus) trituberculatus in Osaka Bay, the carapace widths of juvenile crabs in shallow areas at Tarui and trawl-caught crabs at Izumisano fishing port were examined. Juvenile crabs inhabited the shallow areas from April to November. There were three groups of crabs. In one group, crabs appeared in July, grew rapidly and migrated offshore in September. In the others, crabs appeared in August or September and those that grew quickly migrated offshore in about October or November (second group) while those that grew less quickly migrated the following July or August (third group). The recruitment period to the trawling area was from July to November and the recruited groups corresponded to the groups in shallow areas. The average carapace width of each group in November was estimated to be 181-182mm (recruited in July-August), 169-172mm (recruited in September, female), 148-152mm (same, male), 144-152mm (recruited in October), and 105-115mm (recruited in November). The growth of crabs is well expressed by a logistic equation or Tanaka's ALOG growth curve.