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<p>The effects of soak time on catch rates and at-retrieval survival of large pelagic fishes (tunas, sharks, billfishes, by-product species, and nontarget teleosts) in the eastern and central Pacific tuna longline fishery were assessed using large-scale data (595 sets) obtained from a longline vessel targeting bigeye tuna <i>Thunnus obesus</i>. Catch and survival were analyzed using zero-inflated generalized linear mixed models with Poisson or negative binomial distributions, and generalized linear mixed models with binomial distributions, respectively. The effects of soak time on catch rates varied among species, showing positive, negative, or no effects. For tunas and billfishes, catch rates generally increased with soak time. The catch rate of bigeye tuna exhibited a nonlinear increase, with a sharp rise at soak times of 10 h or less. At-retrieval survival declined with increasing soak time for most species, although the magnitude of decline differed among taxa. Sharks (e.g., blue shark <i>Prionace glauca</i>) showed relatively high survival rates even at longer soak time, despite an increasing trend in catch rate with soak time. We discuss that reducing number of hooks deployed at shorter soak time (≤ 10&#xa0;h) can mitigate reduction in catch rates, increase the proportion of live-caught bigeye tuna, and reduce crew workload.</p>

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Effect of soak time on catch and at-retrieval survival of pelagic fishes caught in the eastern and central Pacific longline fishery targeting bigeye tuna Thunnus obesus

  • 期刊论文

  • 发表日期：

    2026年3月28日

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  • Kosuke Yokota,
  • Takayoshi Uehara,
  • Hiroshi Okamura,
  • Takahisa Mituhasi

摘要

The effects of soak time on catch rates and at-retrieval survival of large pelagic fishes (tunas, sharks, billfishes, by-product species, and nontarget teleosts) in the eastern and central Pacific tuna longline fishery were assessed using large-scale data (595 sets) obtained from a longline vessel targeting bigeye tuna Thunnus obesus. Catch and survival were analyzed using zero-inflated generalized linear mixed models with Poisson or negative binomial distributions, and generalized linear mixed models with binomial distributions, respectively. The effects of soak time on catch rates varied among species, showing positive, negative, or no effects. For tunas and billfishes, catch rates generally increased with soak time. The catch rate of bigeye tuna exhibited a nonlinear increase, with a sharp rise at soak times of 10 h or less. At-retrieval survival declined with increasing soak time for most species, although the magnitude of decline differed among taxa. Sharks (e.g., blue shark Prionace glauca) showed relatively high survival rates even at longer soak time, despite an increasing trend in catch rate with soak time. We discuss that reducing number of hooks deployed at shorter soak time (≤ 10 h) can mitigate reduction in catch rates, increase the proportion of live-caught bigeye tuna, and reduce crew workload.