The catch of large quantities of sublegal-sized fish and shrimp is a pervasive feature of bottom trawl fisheries, particularly in the Mediterranean demersal mixed fisheries where regulations traditionally allow small mesh sizes. To address these concerns, two bottom trawl net selectivity trials were carried out in 2019 and 2020 on fishing grounds worked by the trawl fleet of Spanish Mediterranean, under normal commercial operating conditions with volunteer trawlers of the local fleet. The traditional otter bottom trawl employed in the demersal mixed fishery was modified with a 50-mm T90 panel on the extension piece under two different configurations (front of the extension piece and back of the extension piece). A second modification consisted of inserting a selective grid in the extension piece of the standard bottom trawl net. The species investigated in the demersal mixed fishery were European Hake Merluccius merluccius, Red Mullet Mullus barbatus, Striped Red Mullet Mullus surmuletus, and the deepwater rose shrimp Parapenaeus longirostris. Important selectivity improvements were observed for European Hake and deepwater rose shrimp, particularly in the selective grid trial, where 95% and 100%, respectively, of undersize specimens escaped through the grid. The design with the T90 panel in the back of the extension piece allowed for a reduction of 35% of sublegal-sized individuals of European Hake, but no difference was gained in the sizes of both Mullus spp. retained in the cod end. The adoption of these gear modifications might contribute to reducing discards of sublegal-sized fractions of the fisheries target species.

中文翻译：

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用于减少地中海底拖网渔业中小鱼和虾副渔获物的两种网具改进的相对捕捞性能

捕获大量低于合法尺寸的鱼和虾是底拖网渔业的一个普遍特征，特别是在地中海底层混合渔业中，传统上法规允许使用小网眼。为了解决这些问题，2019 年和 2020 年在西班牙地中海拖网船队工作的渔场进行了两次底拖网选择性试验，在正常商业运营条件下，当地船队的志愿拖网渔船。在底层混合渔业中使用的传统水獭底拖网在两种不同的配置下（延伸件的前部和延伸件的背面）在延伸件上改装了 50 毫米 T90 面板。第二个修改包括在标准底拖网的延伸件中插入一个选择性网格。Merluccius merluccius、Red Mullet Mullus barbatus、Striped Red Mullet Mullus surmuletus和深水玫瑰虾Parapenaeus longirostris。观察到欧洲无须鳕和深水玫瑰虾的选择性提高，特别是在选择性网格试验中，分别有 95% 和 100% 的小样本通过网格逃逸。在允许减少欧洲鳕鱼的sublegal大小个体的35％延伸片背面的T90面板的设计，但没有差别在两者的尺寸是获得Mullus属 保留在鳕鱼末端。采用这些渔具改造可能有助于减少渔业目标物种低于法定规格的部分的丢弃物。