底拖網漁業的網目選擇性研究－Ⅰ-50 mm網目選擇性試驗的初步報告

The Mesh Selection of Bottom Trawl Net*-Ⅰ(Primary Report on the Selection of Cod end with 50 mm Mesh)

周耀烋(Y. S. Chow) ； 謝寬永(K. Y. Hsieh)

《臺灣水產學會刊》 6卷2期 (1979/06) Pp. 42-58

https://doi.org/10.29822/JFST.197906.0005

摘要

為探討本省底拖網漁業的綱目選擇性，進行50mm綱目及16mm的雙重袋網作業試驗，初步獲得的結果摘要如下：
1．狗母類及下雜魚的漁濩量在本地區佔有重要地位。
2．狗母、鞍斑紅魚、衫爪紅魚及瘦帶等魚類，綱目選擇作用甚為明顯。且選擇域亦廣泛。選擇作用較不顯明者，為狗腰鰏（三角仔），黄带鬚鯛（鬚哥）、鰺類等。而該魚種的選擇域亦較為窄狭。
3．狗母、紅魚類的選擇曲線，狀似S字型，上下限附近成平行延伸，中間成急劇下降。上下限之平行部分顯示選擇作用遲緩之體長域，變化劇烈部位，表示選擇作用特別尖銳之區域。瘦帶之選擇曲線較為平緩，說明拖網的綱目選擇作用，對該魚種並無特別敏感的體長羣。
4．50mm綱目的50%選擇率，其對應體長，狗母為158mm，瘦帶120mm，鞍斑紅魚為148mm，衫爪紅魚118mm。
5．50mm綱目的漁獲組成，除小型鰏科下雜魚幾為百分之一百脫離網外，其他魚類約有50%逃脫，該漁獲的變動，對小型單拖的作業，影響不能忽視。
6．本網具試驗，確認綱目的選擇作用，是在有效正常狀態下進行。

並列摘要

In order to find out the mesh selectivity of trawl net, the 50mm of cod end and 16mmcover net in mesh size were used, and a total of 15 experimental hauls in four cruises were made in the water along the coast off Fan-Liao, Fan-San, and Hai-Ko in May and August 1978, respectively (Fig. 1, Tab. 2) Numbers and body length of fishes retained in cod end and cover net were recorded. The experimental results were summerized as follows:
1. The selection ranges in body length for Saurida sp., Nemipterus ovenii, Nemipterus bathybius and Terichirus japonicus were found wider than the other species due to higher sensitive mesh selection. (Tab. 3)
2. The selection curves for Saurida sp., N. ovenii and N. bathybius were ”S” shaped, while that for T. japonicus was a simple smooth curve, (Fig. 3)
3. The mean body length for each species estimated at the 50% selection point was158mm for Saurida sp., 148mm for Nemipterus ovenii, 118mm for Nemipterus bathybius, and 120mm for Trichiurus japonicus.
4. Trash fishes less than 50mm in body length were all escaped from the cod end, but only about 50% of other species were escaped. The amount of cathes will be greatly reduced due to the enlargement of mesh size.
5. The resistance of trawl net with covering net on cod end was increased 11% of total drag force under 3.4 konts of towing speed.