We newly developed a fishing gear
Vertical
Longline for
Sharks(VLS)to effectively study the depth distribution of sharks, and compared its efficiency with that of horizontal longlines. This gear consists of a main line(245 m), branch line(5 m each), and galvanized iron hooks(13 pcs). Trial operations with VLS were conducted monthly in Sagami Bay from July 2014 to February 2016 using RT/V Seiyo Maru(170 t)of Tokyo University of Marine Science and Technology. The problems of VLS were twisting of the main line and the branch lines, which often caused tangling to each other. Making major adjustment 5 times through 20 trial operations, we reduced the rate of the branch lines’ tangling by 16% and improved the working efficiency of VLS. Based on the results, we discussed the causes of(1)the main line’s twisting and (2)the branch lines’ tangling. Catch per unit effort (CPUE: number of sharks captured per 1,000 hooks) of VLS was 9.7, showing the fishing efficiency was comparable to horizontal longlines conventionally operated in Sagami Bay. To be noted is that Shortfin mako shark was captured for the first time during the operation in January 2015, and eventually 6 sharks in total by February 2016.
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