1National Research Institute of Fisheries Engineering, Fisheries Research Agency, Hasaki, Ibaraki 314-0421, 2Seikai National Fisheries Research Institute, Fisheries Research Agency, Nagasaki, Nagasaki 851-2213, Japan
Carapace widths of the red queen crab Chionoecetes japonicus were estimated using the video images taken with a deep-sea video monitoring system on a towed sledge (DVMSTS). A formula to convert the position on the video image to the real scale on the sea floor has been developed. The conversion was calibrated based on video images of a perspective grid recorded by DVMSTS in an experimental tank. In the in situ observation, the points of interest (left and right edges of a carapace) are above the sea floor and this causes an estimation error. By correcting the error, we obtained an accurate estimation of carapace width. The error ranged within ±10 mm when the sample was approximately within 500 mm from the sledge of DVMSTS.