Table_1_Exploring the feasibility of technological transfers of two by-catch reduction devices in the crustacean bottom trawling of the central Mediterranean.docx

IntroductionMost Mediterranean fish stocks are overexploited owing to high fishing efforts and poor exploitation patterns. Demersal trawl fisheries are considered the most impactful fishery type because of the high quantities of unwanted catch that is then routinely discarded at sea.
MethodsIn the present study, two types of by-catch reduction devices (BRDs), that is a sorting grid (Grid-T45 40 mm) and a T90 50 mm codend, were compared to a typical commercial bottom trawl net (control) in terms of size structures and catch per unit effort to assess the effect of gear modification on the selectivity of crustacean fisheries in the central Mediterranean Sea. In particular, three randomly selected trawlers were involved in a paired hauls experiment fishing at the same time in the same fishing ground. Each trawler carried out four hauls per day during a 3-day campaign for a total of 36 hauls. The target species of the fishery is Parapenaeus longirostris (herein DPS), and the main commercial by-catch is Merluccius merluccius (herein HKE).
ResultsThe results showed that the landing per unit effort (LPUE) of DPS was higher for Grid-T45 40 mm net, although it did not differ significantly from that of the control net. Conversely, the discard per unit effort (DPUE) of the control net was significantly higher than of both BRD configurations. For HKE, a slightly higher LPUE was recorded using the T90 50 mm codend compared to that of the control, but this result was not statistically significant. The lowest DPUE was found for the T90 50 mm codend, with significant differences compared to that of the control and Grid-T45 40 mm net. The catch comparison of the size structures analysed through generalised linear mixed models highlighted that the Grid-T45 40 mm net was more effective in catching adult DPS, whereas the T90 50 mm codend was more selective for adult HKE.
DiscussionIn conclusion, although further studies should be carried out in future to test the performance of the BRDs in different areas and seasons, the investigated gear seems to be promising for reducing the catch of undersized individuals and contributing to mitigating the current overfishing of DPS and HKE.

引言
地中海多数鱼类种群因捕捞强度过高、作业模式不合理而处于过度捕捞状态。底拖网渔业因产生大量非目标渔获并常于海上弃置，被认为是影响最为显著的渔业类型。

方法
本研究选取两种副渔获减少装置（by-catch reduction devices, BRDs）——分选栅格（sorting grid，Grid-T45 40 mm）与T90 50 mm拖网囊网（codend），与典型商业底拖网（对照组）进行对比，基于体长结构与单位捕捞努力量渔获量（catch per unit effort, CPUE），评估渔具改造对地中海中部甲壳类渔业选择性的影响。具体而言，随机选取3艘拖网渔船开展配对拖网试验，于同一渔场同时作业。为期3天的试验中，每艘渔船每日开展4次拖网作业，总计36次有效拖网。该渔业的目标物种为长额对虾（Parapenaeus longirostris，本文简称DPS），主要商业性副渔获为欧洲无须鳕（Merluccius merluccius，本文简称HKE）。

结果
研究结果显示，Grid-T45 40 mm拖网的长额对虾（DPS）单位上岸量（landing per unit effort, LPUE）更高，尽管与对照组拖网无显著差异。与之相反，对照组拖网的单位丢弃量（discard per unit effort, DPUE）显著高于两种副渔获减少装置。对于欧洲无须鳕（HKE），T90 50 mm拖网囊网的LPUE略高于对照组，但该差异未达到统计学显著水平。T90 50 mm拖网囊网的DPUE最低，与对照组及Grid-T45 40 mm拖网均存在显著差异。通过广义线性混合模型（generalised linear mixed models）对体长结构开展的渔获对比分析表明，Grid-T45 40 mm拖网对成年长额对虾的捕捞效率更高，而T90 50 mm拖网囊网对成年欧洲无须鳕的选择性更强。

讨论
综上，尽管未来仍需开展更多研究以验证该副渔获减少装置在不同海域与季节的作业性能，但本研究测试的渔具在减少规格不达标的个体渔获、缓解长额对虾与欧洲无须鳕当前的过度捕捞态势方面展现出应用潜力。