房総沖・相模湾のイバラガニモドキ(Lithodes aequispina BENEDICT)調査

The anomuran crab, Lithodes aequis pina BENEDICT, is a species allied to the famous northern king crab, Paralithodes camtschatica (TILESIUS). In spite of the high commercial value of Lithodes aequis pina, the species has been confused with other Paralithodes and Lithodes species in the catch statistics. 1) A biological and fisheries survey on Lithodes aequispina was conducted by the Fisheries Experiment Station of Chiba Prefecture on the ocean floor from 400 to 900 meters depth off Boso Peninsula, Chiba (Fig. 2), and in Sagami Bay (Fig. 3) from November 1968 to March 1970. 2) By setting 11,045 crab pots (Fig. 1) during 104 operations, a catch rate of 0.345 crabs per pot was obtained. There was no great difference in localities except for a very poor catch in Sagami Bay, but there was an irregular seasonal variation in catch per pot, generally decreasing from summer to winter (Fig. 4). The results suggest that the fishing efforts will not be compensated by the market value at this stage. 3) Carapace width range from 8.3 to 19.2cm in the females and from 8.0 to 22.0cm in the males (Fig. 5). The maximum size of the adult crabs was 22.0cm in the males and 19.2cm in the females in this observation. 4) The minimum size of the females incubating eggs on their appendages was 10.5cm in carapace width (Fig. 6). Fifteen per cent of females of 12.6cm in carapace width carried eggs and 60per cent of the females of 13.6cm in carapace width carried eggs. In this paper the females larger than 13.6cm in carapace width are treated as adults. 5) It is assumed that the spawning period continued from July to October ; the incubating period continued from October to February in the following year ; and the hatching period continued from February to July (Fig. 7). The sex ratio in the fishing grounds altogether (400-900 meters depth) was nearly 1 : 1 in the spawning season, while the ratio of the females increased in incubating and hatching periods (Fig. 8). 6) The ratio of the adults to immature (adults/immature) forms was about 3 : 4 from June to September and about 7 : 3 from October to December. At a depth of 400-600 meters the ratio between the adults and immatures was high, while at a depth of more than 600 meters it was low (Fig. 9). 7) The number of incubating eggs at the new egg stage was correlated with the carapace width of the crab at the coefficient of correlation, 0.648. The number of eggs ranged from 9,500 to 30,100 per individual female from 12.9cm to 15.7cm in carapace width (Fig. 10).