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<p>The hydrodynamic properties of hook and bait directly affect the sinking depth of the longline gear. This study, conducted in a flume tank, examined the hydrodynamic coefficients of two hook types, three bait species, and their combination (referred to as baited hook) in both horizontal and vertical orientations. Empirical formulas were derived through nonlinear fitting based on current speed and angle of attack. The results show that: (1) as the Reynolds number increases, both the drag and lift coefficients of the hook decrease and tend to stabilize within a Reynolds number range of 2455–4364; (2) significant differences in drag and lift coefficients were observed among bait types, where squid exhibiting the lowest drag coefficient and a relatively high lift coefficient; (3) baited hooks showed significantly lower drag and lift coefficient compared with unbaited hooks. On the basis of these findings, the following recommendations are proposed: (1) squid baited hooks should be deployed in a horizontal hanging mode to reduce drag and enhance sinking speed; (2) Sardine or Pacific saury baited hooks should be deployed in a vertical hanging mode using 14/0 circle hooks, which may better utilize their hydrodynamic characteristics to accelerate descent during longline deployment.</p>

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Hydrodynamic coefficient of tuna longline hook, bait and baited hook based on flume tank test

  • 期刊论文

  • 发表日期：

    2025年9月9日

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  • Bo Zhang,
  • Liming Song,
  • Yuwei Li,
  • Yukun Qi,
  • Linhui Wang,
  • Meng Zhang,
  • Hailin Hao

摘要

The hydrodynamic properties of hook and bait directly affect the sinking depth of the longline gear. This study, conducted in a flume tank, examined the hydrodynamic coefficients of two hook types, three bait species, and their combination (referred to as baited hook) in both horizontal and vertical orientations. Empirical formulas were derived through nonlinear fitting based on current speed and angle of attack. The results show that: (1) as the Reynolds number increases, both the drag and lift coefficients of the hook decrease and tend to stabilize within a Reynolds number range of 2455–4364; (2) significant differences in drag and lift coefficients were observed among bait types, where squid exhibiting the lowest drag coefficient and a relatively high lift coefficient; (3) baited hooks showed significantly lower drag and lift coefficient compared with unbaited hooks. On the basis of these findings, the following recommendations are proposed: (1) squid baited hooks should be deployed in a horizontal hanging mode to reduce drag and enhance sinking speed; (2) Sardine or Pacific saury baited hooks should be deployed in a vertical hanging mode using 14/0 circle hooks, which may better utilize their hydrodynamic characteristics to accelerate descent during longline deployment.