EFFECTS OF TIME OF SOLAR DAY, JIGGING METHOD AND JIGGING DEPTH ON CATCH RATES AND SIZE OF GOULDS SQUID, NOTOTODARUS-GOULDI (MCCOY), IN SOUTHEASTERN AUSTRALIAN WATERS

Three squid-jigging experiments were conducted from 29 December 1980 t o 12 April 1981 on FV Hoyo Maru 81. The aim was to determine the effec ts of time of night or day and of depth of setting jigs controlled by jig-line length on catch rates and mantle length of Gould's squid take n by machine-jigging and hand-jigging methods. Each machine had two ji g-lines with 25 jigs on each jig-line and each hand-jigging fisher use d one line with a single jig. Catch per unit effort (CPUE) expressed a s weight of squid per machine-hour or weight of squid per hand-jigging fisher-hour was higher for the hand-jigging method than for the machi ne-jigging method at all times over the 24-h period. CPUEs were higher during the night than during the day for both methods, and, apart fro m lower CPUEs during the first 2 h of the night, CPUEs were steady thr ough the night. CPUEs for hand-jigging from the surface to > 80 m dept h exceeded those for machine-jigging in the depth-range 0-80 m and CPU Es for machine-jigging declined as the depth-range was reduced from 0- 80 m to 0-40 m. Mean mantle lengths of both female and male squid caug ht by hand-jigging were greater than those caught by machine-jigging a t all times and all depths. Mean length for machine-jigging declined a s depth-range was reduced from 0-80 m to 0-40 m. Diel vertical migrati on of squid, whereby small squid tend to rise higher in the water colu mn than large squid during darkness, is advanced as a hypothesis to ex plain these patterns. Other factors that could have contributed to the pattern of catches include time out of the water by jigs not fishing between jigging cycles, gear competition between jigs, and short-term localised depletion of squid in the immediate vicinity of the jigs. (C ) 1998 Elsevier Science B.V.