Fish Capture Division, Institute of Marine Research (IMR), Bergen, Norway.
Department of Biological Sciences, University of Bergen, Bergen, Norway.
PLoS One. 2019 Mar 13;14(3):e0213709. doi: 10.1371/journal.pone.0213709. eCollection 2019.
Stress to fish during harvest in wild capture fisheries is known to negatively influence subsequent survival in catches that are released. Therefore, if fisheries are to be conducted sustainably, there is a need to promote good fish welfare during the capture process. Purse seine fishing is a widespread and efficient fishing method. However, capture and release of fish from purse seines (a process called "slipping") can result in extremely high mortality in small pelagic schooling species. The objective of this study was to establish behavioural indicators of sub-lethal stress in Atlantic mackerel (Scomber scombrus) that may be used to set safe threshold limits for use in commercial purse seine fishing, in order to ensure good fish welfare and thereby minimise slipping mortality. Controlled mesocosm scale experiments with schools of mackerel in net pens were undertaken to determine behavioural responses to simulated purse seine capture stressors of "crowding", "hypoxia" and "crowding & hypoxia". Crowding (at 30 kg.m-3) was achieved by reducing the volume of the net pen, while hypoxia (to 40% oxygen saturation) was achieved by surrounding the net pen with a tarpaulin bag to prevent water exchange. Using video analysis, we investigated behavioural responses in nearest neighbour distances, nearest neighbour angular deviations, tail beat amplitude and tail beat frequency (TBF). Of the metrics considered, only TBF showed a response; a significant increase to "crowding" (42% increase) and "crowding & hypoxia" (38% increase) was found. The increase in TBF in response to "hypoxia" alone (29% increase) was not significant. We therefore conclude that increases in tail beat frequency may be used as an indicator of sub-lethal purse seine capture stress in mackerel that may have utility in minimising post slipping mortality.
在野生捕捞渔业中，鱼类在收获过程中所承受的压力已知会对随后在被释放的渔获物中的生存产生负面影响。因此，如果要可持续地进行渔业，就需要在捕捞过程中促进鱼类的良好福利。围网捕鱼是一种广泛而高效的捕鱼方法。然而，从围网中捕获和释放鱼类（称为“滑脱”）可能导致小型中上层洄游鱼类的死亡率极高。本研究的目的是确定大西洋鲭（Scomber scombrus）的亚致死应激行为指标，这些指标可用于为商业围网捕鱼设定安全阈值，以确保鱼类福利良好，从而最大限度地减少滑脱死亡率。在网箱中进行了带有鲭鱼鱼群的受控中观尺度实验，以确定对模拟围网捕捞应激源“拥挤”、“缺氧”和“拥挤和缺氧”的行为反应。通过缩小网箱的体积来实现拥挤（30 kg.m-3），通过用防水布围绕网箱来防止水交换来实现缺氧（40%的氧气饱和度）。使用视频分析，我们研究了最近邻居距离、最近邻居角偏差、尾拍幅度和尾拍频率（TBF）的行为反应。在所考虑的指标中，只有 TBF 显示出反应；发现“拥挤”（增加 42%）和“拥挤和缺氧”（增加 38%）时 TBF 显著增加。单独“缺氧”时 TBF 的增加（增加 29%）并不显著。因此，我们得出结论，TBF 的增加可能被用作鲭鱼亚致死围网捕捞应激的指标，这可能有助于最大限度地减少滑脱后死亡率。
