SIZE-SELECTIVITY AND CATCHING EFFICIENCY OF 3 DIFFERENT TRAPS FOR WHELKS NEPTUNEA-ARTHRITICA IN SHIRIUCHI, HOKKAIDO

In an attempt to find suitable fishing gear solely to trap whelks Nept unea arthritica, three different trap designs were used to carry out a preliminary survey. Trap A had two entrances from the side, while tra ps B and C had one entrance on the top. A string of thirty traps set i n order of trap A, trap B, and trap C and baited with about 900g of sa rdine were set at depths between 21 to 23m. In the four samplings cond ucted between July to December 1991, the soak time varied from 19h to 23h. The catch number differed significantly between the traps. The av erage catch number per trap/day in trap A was 43.9, in trap B 62.0, an d in trap C 37.1. Mean catch rates in terms of weight varied from 1.40 kg/trap in A, 2.22kg/trap in B, and 1.18kg/trap in C. The mean shell l ength taken by traps A, B, and C was between 61mm and 63mm. The overal l results obtained from traps A, B, and C revealed that trap B was the most efficient for catching whelks. The present traps used in our sur vey were non-selective in catching whelks.