Page 336 - 《水产学报》2026年第04期

4 期 晏 磊，等：南海张网不同尺寸的 T90 网目网囊对凤鲚和周氏新对虾的选择性 50 卷

Size selectivity of T90 mesh codends in stow net for Coilia mystus and
Metapenaeus joyneri in the South China Sea

YAN Lei , LI Jie , YANG Bingzhong , WANG Teng , CHEN Zuozhi , ZHANG Peng *
(Key Laboratory for Sustainable Utilization of Open-sea Fishery, Ministry of Agriculture and Rural Affairs,
South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China)

Abstract: Stow net fishery is one of the most important components in coastal waters of China, characterized by simple gear
structure, low energy consumption and stable economic benefits. In the South China Sea, two-stick stow net is widely used to
harvest small fish and crustaceans, especially Coilia mystus and Metapenaeus joyneri. However, traditional stow net usually
employ small mesh sizes and diamond-shaped meshes, resulting in poor size selectivity and high bycatch rates of juveniles,
which pose serious threats to sustainable exploitation of coastal fishery resources. Codend structure, particularly mesh size and
mesh orientation, plays a key role in determining the geometric configuration, hydrodynamic performance and selective proper-
ties of stow net. Compared with conventional diamond meshes, T90 meshes (diamond meshes rotated by 90°) have been proven
to maintain more stable opening geometry and better selectivity in trawl fisheries, but their effectiveness in passive stow net
systems remains insufficiently quantified. The objective of this study was to quantify the size selectivity of T90 mesh codends
with different mesh sizes used in two-stick stow net fisheries in the South China Sea, and to evaluate their effects on the select-
ive properties for C. mystus and M. joyneri, providing a scientific basis for codend design optimization and mesh size regula-
tion. Field selectivity experiments were conducted using the covered method with T90 mesh codends of three mesh sizes (30,
35, and 40 mm). Catch data from the codend and the cover net were collected and sorted by size. Logistic and Richards models
were applied to fit the size selectivity curves for C. mystus and M. joyneri, and selectivity parameters, including the 50% selec-
tion length (L 50 ), were estimated using the maximum likelihood method. The relationship between L 50 and mesh size was fur-
ther analyzed to estimate the minimum appropriate mesh size for each target species. The results showed a clear increase in size
selectivity with increasing mesh size. For C. mystus, the estimated L 50 values were 130.88 mm, 134.04 mm, and 142.72 mm for
the 30, 35, and 40 mm T90 mesh codends, respectively. For M. joyneri, the corresponding L 50 values were 70.75 mm, 79.93
mm, and 90.10 mm. In both species, L 50 increased consistently with mesh size, indicating enhanced release of smaller individu-
als. Based on the linear relationship between L 50 and mesh size, the minimum appropriate mesh sizes were estimated to be
28.20 mm for C. mystus and 29.51 mm for M. joyneri. Considering the body shape characteristics of the target species and the
selectivity results, it is recommended that the minimum mesh size of T90 codends used in two-stick stow net fisheries in the
South China Sea should not be less than 30 mm. Compared with traditional diamond meshes, T90 mesh codends can maintain
higher opening stability and significantly improve the release efficiency of juvenile fish and shrimp. These findings demon-
strate that adopting T90 mesh structures is an effective technical measure to improve stow net selectivity and contribute to the
sustainable management of coastal fishery resources in the South China Sea.
Key words: Coilia mystus; Metapenaeus joyneri; stow net; T90 mesh; selectivity

Corresponding author: ZHANG Peng. E-mail: trawl@126.com
Funding projects: National Key R & D Program of China (2024YFD2400404); Special Financial Project of the Ministry of
Agriculture and Rural Affairs (NFZX2024)

中国水产学会主办 sponsored by China Society of Fisheries https://www.china-fishery.cn
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