Abstract The escape of small smolt through farm cage netting is a major challenge faced by the Norwegian salmon farming industry. Escape can occur when the smolt placed in the cages are smaller than the size estimated by the farmers. Furthermore, one may assume wrong mesh-properties as the cage netting change shape and/or state from stiff (mesh bars with tension) to slack (mesh bars without tension) due to sea currents or waves and become more suitable for penetration. The latter represents an increased risk for cages placed in more exposed sea areas, which is a growing trend in the industry due to increased demand for farming sites. The potential influence of mesh shape and state on the risk of escape from salmon farm cages is predicted. The morphological characteristics of salmon smolt are assessed and used to determine the risk of potential escape through meshes of different sizes, shapes and states. The results showed that fish smaller than 47 g and 201 g have the potential to escape through 30 mm and 50 mm meshes, respectively. In general, the risk of smolt escape is highest when the meshes in the netting are slack. Semi-slack meshes with mesh openness of between 65 and 95 % also present a higher risk of smolt escape than square stiff meshes. The highest risk of escape was identified at approximately 80 % mesh openness. This study illustrates the importance of mesh states in fish farming cage nettings. In many cases the minimum smolt size needed to maintain an escape risk below 1 % was approximately twice as large for slack square meshes than for stiff square meshes of the same size.

中文翻译：

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预测鲑小鲑（Salmo salar）通过养鱼场网逃逸的大小相关风险

摘要 小鲑鱼通过养殖场笼网逃逸是挪威鲑鱼养殖业面临的主要挑战。当放置在笼子里的小黑鱼小于农民估计的大小时，就会发生逃跑。此外，由于海流或波浪使笼网的形状和/或状态从刚性（有张力的网条）变为松弛（没有张力的网条），并且变得更适合穿透，因此人们可能会假设错误的网状特性。后者代表将网箱放置在更暴露的海域的风险增加，由于对养殖场所的需求增加，这是该行业的增长趋势。预测网格形状和状态对从鲑鱼养殖场网箱逃逸风险的潜在影响。对鲑鱼的形态特征进行评估并用于确定通过不同尺寸、形状和状态的网眼可能逃逸的风险。结果表明，小于 47 克和 201 克的鱼分别有可能通过 30 毫米和 50 毫米的网孔逃脱。一般而言，当网中的网眼松弛时，幼鱼逃逸的风险最高。网孔开度在 65% 到 95% 之间的半松散网孔也比方形刚性网孔有更高的脱毛风险。在大约 80% 的网孔开口处确定了最高的逃逸风险。本研究说明了网状状态在养鱼网箱中的重要性。