台灣沿近海不同網目的單層與三層刺網之魚種選擇性與大小選擇性研究

Abstract

刺網漁業為台灣沿近海域最重要的漁業之一，漁民會在特定的季節使用特定網目的單層網或三層網作業，以期捕獲特定大小的目標魚種。本研究之目的，即在探討這些刺網的魚種選擇性及大小選擇性。本研究於2000-2002年期間，在桃園竹圍漁港以及宜蘭梗枋漁港委託刺網漁船進行漁獲比較試驗，並針對魚市場之刺網漁獲物進行採樣。竹圍地區使用包括網目2.7寸、3.8寸、4.0寸、4.5寸、5.3寸、6.0寸之單層網，以及內層網目2.7寸、3.4寸、3.8寸、4.5寸、5.5寸之三層網。梗枋地區使用包括網目3.0寸之單層網以及內層網目2.8寸之三層網（一寸＝3.03cm)。魚種選擇性部份，利用相似度係數、集群分析法、歧異度指數進行分析。大小選擇性部份，藉由體長、眼圍、頭圍、最大體圍等計量形質，以體圍形質推定法估計理論曲線。結果顯示，不同網具之相似度偏低，顯示各種網具之魚種選擇性有所不同，其中又以網目2.7寸之單層網漁獲組成最為特殊，異於三層網及大網目之單層網。多數網具之歧異度偏高，顯示刺網對漁業資源之利用方式呈現多樣性，也就是魚種專一性不高。以刺入方式被捕獲的魚種，其漁獲部位大多介於頭圍與最大體圍之間。配合網目的修正，各主要漁獲魚種的選擇曲線均可由體圍形質推定法獲得良好套適。

Gillnet fishery is one of the most important fisheries in the coastal and offshore waters of Taiwan. The fishermen usually catch the specific size fishes of target species by some gillnets and/or trammel nets with various mesh sized. The purpose of this study is to investigate the species and size selectivity of gillnets and trammel nets with various mesh sizes in the area. The comparing experiments between gears were undertaken in the fishing harbors of Zhu-Wei, Tao-Yuan County and Gen-Fan, I-Lan County by the chartered fishing vessels from 2000 to 2002. In addition, many catches of gillnet vessels in the two fishing harbors were also measured. The mesh sizes 2.7, 3.8, 4.0, 4.5, 5.3, and 6.0 Taiwanese inch (1 Taiwanese inch = 3.03cm) of gillnets as well as 2.7, 3.4, 3.8, 4.5, and 5.5 inch of trammel nets were adopted in the fishing harbor of Zhu-Wei, Tao-Yuan County. The gillnet with mesh size 3.0 inch and the trammel net with 2.8 inch were also adopted in the fishing harbor of Gen-Fan, I-Lan County. The comparisons of species selectivity between gears were undertaken by the similarity coefficient, cluster analysis, and diversity index. The size selectivity curves of dominant species were estimated by the Sechin method (inference from girth measurements) for the measuring variables of fork length, eye girth, head girth, and maximum body girth. The results were as follows. The low similarity coefficients between gears indicated that the species selectivity was dispersed between gears. The catch composition of gillnet with 2.7 inch size was the most special among all gears. The high diversity indices of most gears indicated that the specific target species of gillnet fisheries were not clear. The caught body positions were between head girth and maximum girth for those enmeshed fishes. The theoretical size selectivity curves estimated by the Sechin method after modifying the variables of mesh sizes were fitted well to the observed data for the most dominant species.