2018 Volume 55 Issue 1 Pages 11-19
Codend opening/closing MOHT （COC-MOHT） was developed by installing the codend frame with five codend nets on the base of the MOHT （Matuda-Oozeki-Hu Trawl）. To investigate the diel vertical migration and net avoidance of lantern fish, three oblique tows from 250 m and 450 m depths to the surface and one horizontal tow at different towing speed of 4, 3 and 2 knots for each codend were conducted using COC-MOHT in Sagami Bay on 16 October 2014 by training vessel Umitaka-Maru belonging to Tokyo University of Marine Science and Technology. Samples were sorted into Myctophidae, Cephalopoda, Euphausiidae, Sergestidae, and other fishes. Lantern fish was measured in standard body length and classified into 5mm intervals. It was found from the result of three oblique tows that lantern fish distributed in the two major depth zones: shallower than 150 m and deeper than 250 m at daytime, depending on the myctophid species. And after sunset, lantern fish migrated from the deeper zone to the shallower zone. In the horizontal tow, Diaphius spp. with SL › 30 mm were less caught at lower towing speed. A possible explanation is that net avoidance of the larger fish occurred because they can generally swim faster.
