秋季莱州湾弓子网网囊网目尺寸选择性研究

Selectivity of Codend Mesh of Beam Trawl in Laizhou Bay in Autumn

中文关键词: 弓子网  莱州湾  逃逸率  选择性  网囊网目尺寸

英文关键词: Beam trawl  Laizhou Bay  Escape ratio  Selectivity  Codend mesh size

中文摘要:

      单船框架拖网(俗称弓子网)是渤海海区常见的作业渔具，对底栖渔业生物选择性差，作业过程中产生大量副渔获物。为改善网囊网目的选择性，2017年9月在莱州湾海域采用“套网法”对网囊网目尺寸分别为15、25、35、45和55 mm的5种网囊进行了选择性实验。结果显示，弓子网对渔获物种类的选择能力较差，具有捕获栖息于作业海域绝大多数底栖种类的能力。随网囊网目尺寸的增加，渔获物质量、尾数逃逸率和产值损失率逐渐增大，短吻红舌鳎(Cynoglossus joyneri)、口虾蛄(Oratosquilla oratoria)、鹰爪虾(Trachypenaeus curvirostris)和日本鼓虾(Alpheus japonicas)的选择性参数(L0.5、SR)呈线性增加。口虾蛄和鹰爪虾的50%选择体长(L0.5)与网目尺寸(m)的线性回归方程分别为L0.5=1.472m+12.63(R2=0.934)和L0.5=1.394m+0.724(R2=0.920)。在目前的渔业资源状况下，为保护口虾蛄和鹰爪虾等经济渔获物资源，兼顾生产效益和幼鱼资源保护，建议将弓子网最小网目尺寸放大至45 mm。

英文摘要:

      The beam trawl is a common fishing gear in the Bohai Sea area and is associated with significant by-catch rates because of its poor selectivity. To improve the selectivity of codend mesh, the authors conducted selective experiments on the codend mesh of beam trawls in the Laizhou Bay during September 2017. A cover net method was used and five kinds of codends (mesh sizes of 15, 25, 35, 45, and 55 mm) were studied. Results show that beam trawls had a poor selectivity for catch species, capturing most of the benefic species in the operating area. Escape rates of the catch in weight, number, and value increased with codend mesh size. The 50% selectivity body length (L0.5) and selection range of Cynoglossus joyneri, Oratosquilla oratoria, Trachypenaeus curvirostris, and Alpheus japonicas linearly with mesh size. The L0.5 of O. oratoria and T. curvirostris appeared to exhibit a linear relationship with codend mesh size (m). Linear regression equations of L0.5=1.472m+12.63 (R2=0.934) and L0.5=1.394m+ 0.724 (R2=0.920), were derived for the respective species. To protect economically valuable species such as O.oratoria, T. curvirostris, the authors suggest enlarging the minimum mesh size for beam trawls to 45 mm, which would maintain production efficiency and protect juvenile fish resources.