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The use of otter guards in fyke net surveys and their effect on catches of European Eel Anguilla anguilla

机译:在Fyke净调查中使用水獭守卫及其对欧洲EEL Anguilla Anguilla捕获的影响

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摘要

The European eel is critically endangered and European member states are required to undertake measures to ensure the recovery of eel stocks. The otter is also a protected species under international legislation. As a predator of the eel the otter is often caught in fyke nets located close to shore and in shallow water and otter guards can be used to reduce this unwanted by-catch. This study was undertaken to investigate the effect of otter guards in fyke nets on 1) eel catch and 2) eel length frequency and to compare with eels caught in non guarded fyke nets. In seven lakes at each net location a combination of guarded and non-guarded fyke nets were set. A generalized linear mixed model analysis (GLMM) was applied to the eel catch data with treatment (guarded/non-guarded) as the fixed effect. The catch model predicts that on average the catch per unit of effort (CPUE) for a guarded fyke net is 0.5 (95 % CI [0.34 - 0.73]) and the CPUE for a non-guarded net is 0.7 (95 % CI [0.48-1.0]). Converting the CPUE to numbers of eels, the model predicts that a guarded net will catch 5 eels (95 % CI [3-7 eels]) and a non-guarded net will catch 7 eels (95 % CI [5-10 eels]). A second GLMM analysis investigated the effect of treatment on the length of eels captured in fyke nets. The predicted mean length of an eel for a guarded net is 48 cm (95 % CI [44-52 cm]), and 49 cm (95 % CI [45-54 cm]) for a non-guarded net. Considering the degree of variation within the lake, these results show that there is no impact on the numbers or the length of eels captured in guarded fyke nets. There are more important variables influencing the eel catch within lakes.
机译:欧洲鳗鱼是危险性濒危,欧洲成员国需要采取措施确保鳗鱼股的恢复。水獭也是国际立法的受保护物种。作为鳗鱼的捕食者,水獭通常捕获位于靠近岸边的Fyke网,浅水区,水獭防护装置可用于减少这种不需要的禁止。本研究旨在探讨欧洲欧利克赛和2)鳗鱼蚊帐的水獭守卫在鳗鱼蚊帐中的效果,并与鳗鱼捕获的鳗鱼相比。在每个净位置的七个湖泊中,设定了守卫和非保护的Fyke网的组合。将广义的线性混合模型分析(GLMM)施加到EEL捕获数据中,用治疗(保护/非保护)作为固定效果。 Catch模型预测,平均防护FYKE网的每单位努力(CPUE)的捕获量为0.5(95%CI [0.34 - 0.73]),非保护网的CPUE为0.7(95%CI [0.48] -1.0])。将CPUE转换为EEL的数量,该模型预测守卫的网将捕获5鳗鱼(95%CI [3-7鳗鱼])和非保护净将捕获7鳗鱼(95%CI [5-10鳗] )。第二种GLMM分析研究了治疗对FYKE网捕获的鳗鱼长度的影响。用于防护网的鳗鱼的预测平均长度为48厘米(95%CI [44-52cm])和49厘米(95%CI [45-54cm]),用于非保护网。考虑到湖内的变化程度,这些结果表明,对守卫的FYKE网中捕获的鳗鱼的数量没有影响。有更重要的变量影响湖泊内的鳗鱼捕获。

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