Abstract

This article describes a method for the quantitative analysis of fish behaviour relative to selection devices in trawl gears. Based on video observations, the method estimates probabilities for a given event to happen and establishes behavioural tree diagrams representing and quantifying behavioural patterns in relation to the selection device under assessment. Double bootstrapping is used to account for the uncertainty originating from a limited number of fish observations and the natural variation in fish behaviour. The method is used here to supplement standard analysis of catch data for the performance assessment of a flatfish excluder (FLEX). The Baltic Sea trawl fishery targeting cod (Gadus morhua) provides the pilot case. Results obtained by comparing catches with and without FLEX installed revealed that >75% of bycaught flatfish individuals escaped through the device, while no evidence was found that catches of cod in the targeted sizes were reduced. The behavioural analysis produced values of escape efficiency comparable to those obtained in the catch analysis. Furthermore, it revealed that ∼80% of the flatfish went calmly into the excluder, while most of the roundfish displayed avoidance swimming reactions. The method provides quantitative information of fish behaviour that can be relevant for developing and optimizing selection devices.

中文翻译：

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通过将捕获数据分析和鱼类行为观察相结合来量化选择性设备的性能：比目鱼排除器的方法和案例研究

摘要

本文介绍了一种相对于拖网渔具选择装置对鱼类行为进行定量分析的方法。基于视频观察，该方法估计给定事件发生的概率，并建立表示并量化与评估中的选择设备有关的行为模式的行为树图。两次自举法用于解释由于有限的鱼类观察和鱼类行为的自然变化而产生的不确定性。该方法在这里用于补充捕获数据的标准分析，以评估比目鱼排除者（FLEX）的性能。针对鳕鱼的波罗的海拖网渔业（Gadus morhua）提供了试点案例。通过比较安装和不安装FLEX的渔获物所获得的结果表明，> 75％的被捕获的比目鱼个体通过该设备逃脱了，而没有证据表明目标尺寸的鳕鱼的渔获量减少了。行为分析得出的逃逸效率值可与渔获分析中获得的值相媲美。此外，它揭示了约80％的比目鱼从容进入了排除对象，而大多数比目鱼则表现出回避游泳反应。该方法提供了鱼类行为的定量信息，这些信息可能与开发和优化选择设备有关。