1Fishing Technology Division, National Research Institute of Fisheries Engineering, Fisheries Research Agency, Ibaraki 314-0421, 2Japan Sea Fisheries Resources Division, Japan Sea National Fisheries Research Institute, Fisheries Research Agency, Niigata 951-8121, Japan
The population density of the snow crab Chionoecetes opilio was investigated using the deep-sea video monitoring system on a towed sledge (DVMSTS). The observations were carried out at seven survey sites ranging from 200 to 340m depth on Aug. 20-29, 1998. These sites were located north and west of the Oki Islands, the Sea of Japan. The Observations were repeated 8 times; 375 minutes of video tapes were recorded. The total observed distances were 15,600m, and the DVMSTS towed sweeping area was a total of 25,900m2 of bottom. The count was 104 crabs. The sweeping area was obtained to multiply the observed distance by the width of the DVMSTS (1.66m). Crab densities per 1,000m2 for each observation were estimated to be 1, 3, 3, 3.1, 4.0, 5.6, 6.4 and 10 individuals, respectively. It was difficult to distinguish males and females among small crabs (<about 9cm carapace width). Because the majority of crabs did not respond to the light, presumably underwater lighting scarcely affects the behaviour of the crab. To utilize this equipment as a quantitative survey method for the snow crab, it is necessary to improve the estimation accuracy of the population density.