まぐろはえ縄漁業における海亀混獲削減を目的として長浮縄を併用した中立ブイ・システム-メバチ釣獲率の向上効果 A Midwater Float System with Long Float Lines for Sea Turtle Bycatch Reduction in Pelagic Longline Fisheries -Potential for Catch Efficiency of Bigeye Tuna Thunnus Obesus

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Abstract

中立ブイと長浮縄を装着した浮延縄漁具を用いた操業実験をインド洋にて実施した。水深計とGPS ブイを用いて漁具各部の水深と短縮率を計測し,漁獲されたメバチの枝縄番号を記録した。中立ブイと長浮縄を装着した漁具では,すべての釣針が150m 以深に設置された。通常鉢での漁獲結果から推定したメバチの水深別CPUE(100 針あたりの漁獲尾数)は,水深150m 以深で高かった。短縮率を0.8 として求めた同漁具の水深層別釣針本数とメバチのCPUE から推定したメバチの漁獲尾数は,通常漁具に比べて約30% 増加した。このシステムは海亀の混獲を低減させつつもマグロ類の漁獲の効率を増加させる可能性がある。

A midwater float system with long (100m) float lines for deep setting of pelagic longline wasdeveloped to reduce sea turtle bycatch and improve fishing efficiency, focusing on the difference inswimming depth between sea turtles and tuna species. Longline setting with midwater floats which aresmall floats attached to the mainline allows all the hooks of one basket to be set within narrower depthrange than the conventional setting. Long float lines could set the main line with all hooks in the deeperrange for tuna habitat to avoid the hooks entering the sea turtle habitat. Longline operations werecarried out in the Indian Ocean. One midwater float with a buoyancy of 2300gf or 2000gf was attached toeach center of five baskets on the mainline, both ends of which were hung with 100m long float lines.The conventional setting with 40m float lines without any midwater float was also conducted as a control.No bycatch of sea turtles occurred in the midwater float setting while one olive ridley sea turtle wascaught in the conventional setting. All hooks of the midwater float settings were set below 150m depth,while the hooks in the conventional setting were set in the wide depth range from 109m to 230m. Thehook position in a basket catching bigeye tuna was recorded to estimate the depth of catching. TheCPUE of bigeye tuna was higher in the hooks below 150m. The estimated catch number of bigeye tunain longlines with midwater float setting was nearly 30% more than using the conventional setting.

Journal

  • Journal of Fisheries Engineering

    Journal of Fisheries Engineering 54(3), 185-195, 2017

    The Japanese Society of Fisheries Engineering

Codes

  • NII Article ID (NAID)
    130007540106
  • NII NACSIS-CAT ID (NCID)
    AN10278554
  • Text Lang
    ENG
  • ISSN
    0916-7617
  • NDL Article ID
    028901150
  • NDL Call No.
    Z18-1327
  • Data Source
    NDL  J-STAGE 
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