Abstract：
Barriers in the estuaries of the rivers prevent the immigration of glass eels (Anguilla anguilla) arriving on the European coast every spring. This leads to an unnatural accumulation of migrating glass eels below the barriers, and this may lead to additional losses in glass eels by piscivorous fish. The proportion of predation losses can be estimated using mark-recapture techniques and abundance estimates in combination with stomach content analysis of piscivorous fish. Nonetheless, whether tagging transparent glass eels increases predation risk and what the digestion rate of glass eel is in piscivorous fish are unknown. This study aimed to determine whether there is an increased predation risk for tagged glass eel; it also studies glass eel digestion status in piscivorous fish after appointed time frames. A laboratory experiment with 48 trials was conducted. Tagged (visible implanted elastomer, VIE) and untagged glass eels were exposed to small (19.1-24.4 cm) and large (31.9-43.5 cm) sea bass (Dicentrarchus labrax) during a 2 h trial. In 48% of the trials, successful predation was present and 13% showed clear predation attempts in which bass did not capture glass eels. No significant difference was found in predation rate between tagged and untagged glass eels and between red and blue tagged glass eels. Large sea bass predated more, but all sizes consumed glass eel under laboratory conditions. Stomach content analysis showed intact glass eel bodies 4-6 h after ending the 2 h trial and parts of glass eel bodies up to 16-18 h. This study showed that tagging does not increase predation in mark-recapture studies using VIE-tags in transparent glass eel. It also shows that the proportion of predation in relation to local glass eel abundance can be estimated if stomach content analysis is conducted within 4-6 h after predation.
摘要：
河流河口的障碍阻止了每年春天到达欧洲海岸的玻璃鳗鱼（安圭拉anguilla）的移民。这导致屏障下方迁移的玻璃鳗鱼不自然地积累，这可能会导致食鱼对玻璃鳗鱼的额外损失。捕食损失的比例可以使用标记再捕获技术和丰度估算结合食鱼的胃含量分析来估算。尽管如此，标记透明玻璃鳗鱼是否会增加捕食风险，玻璃鳗鱼在食鱼中的消化率是多少，目前尚不清楚。这项研究旨在确定标记的玻璃鳗鱼的捕食风险是否增加；它还研究了指定时间框架后食鱼鱼的玻璃鳗鱼消化状况。进行了48个试验的实验室实验。标记(可见植入弹性体，VIE）和未标记的玻璃鳗鱼在2小时的试验中暴露于小（19.1-24.4厘米）和大（31.9-43.5厘米）鲈鱼（Dicentrarchuslabrax）。在48%的试验中,存在成功的捕食，并且13％的人表现出明显的捕食尝试，其中鲈鱼没有捕获玻璃鳗鱼。标记和未标记的玻璃鳗鱼之间以及红色和蓝色标记的玻璃鳗鱼之间的捕食率没有显着差异。大鲈鱼早于更多，但是在实验室条件下所有尺寸都会消耗玻璃鳗鱼。胃含量分析显示，在2小时试验结束后4-6小时，完整的玻璃鳗鱼体和部分玻璃鳗鱼体长达16-18小时。这项研究表明，在使用透明玻璃鳗鱼中的VIE标签的标记-捕获研究中，标记不会增加捕食。它还表明，如果在捕食后4-6小时内进行胃内容物分析，则可以估计捕食与当地玻璃鳗鱼丰度的比例。
