台灣東北海域花腹鯖（Scomber australasicus）單位加入生產量之研究

Abstract

花腹鯖（Scomber australasicus）是台灣鯖魚產業中產量最高的魚種，至1980年後，從日本引進鯖鰺大型圍網來開發利用此資源，近十幾年來圍網船數固定有八艘在沿近海從事漁撈作業，為近海漁業漁獲效率最高之漁法，主要漁場位於台灣東北海域與西南海域（東北漁場淡季才轉至此），因近年來產量變動幅度大且有持續下滑的趨勢，迫使本研究針對單一漁具行為進行台灣東北海域花腹鯖資源現況調查。 本研究採樣期間從2004年四月至2005年五月，每月利用分層採樣法在蘇澳鎮之冷凍加工場內進行量取樣本尾叉長(Fork Length)。實際量側體長頻度資料共有14,836筆，範圍介於18.5公分至41.5公分（尾叉長），另外尚在生殖季節期間共收集了351對生殖腺，推估其50%成熟年齡（tm）落於1.11-0.96歲之間。利用每月體長頻度資料以ELEFAN I 來推估von Bertalanffy成長方程式，其成長參數Lmax 、K和 to分別為 43.58公分、 0.67 (/年)及 -0.20(歲)。體長體重關係式，參數 和 分別為0.008530019與3.1 ( a，b )。全死亡率為3.51 (/年)，自然死亡率由Pauly經驗式推估可得1.15 (/年)，經計算後開發比例(E )達0.67。 單位加入生產量模式分析結果，現階段的漁獲死亡率（Fcur=2.36 /年）已超過最大漁獲死亡率（Fmax=2.01 /年）及管理上的生物參考點（F0.1=0.91）。亦可從單位加入生產親魚量模式得知，目前生殖潛能比例（Spawning Potential Ratio）只剩下5%-7%（tm=0.96-1.11 歲），均顯示台灣東北海域花腹鯖現階段有過漁現象，該資源已有管理上的必要。

This study was done to assess the dynamics of the exploited population for Scomber australasicus (spotted mackerel), which is the most important species of the large-type of purse seines in the inshore waters of northeastern Taiwan. From April 2004 to March 2005, total of 14,836 fish ranging from 18.5 to 41.5 cm were measured on landing data on Su-auo port. The parameters of the von Bertalanffy growth equation were: asymptotic length (Lmax )=43.58 cm (Fork Length), growth coefficient (K)=0.67 year−1, and age at zero length (to)=-0.2 year. The length-weight relationship was ( a, b). In the main spawning season, the reproduction samples were collected during the February to April and the fork length at 50% maturity was estimated from 23.5 to 25.5 (cm). The instantaneous rates of total mortality (Z), natural mortality (M) and fishing mortality (F) were 3.51, 1.15 and 2.36 per year, respectively. Besides, the estimate of exploitation ratio (E) was 0.67. According to the yield-per-recruit and spawning biomass-per-recruit analysis showed that the current fishing mortality (Fcur ) was beyond the maximum fishing mortality ( Fmax=2.01 ) and biology reference point (F0.1 =0.91 ). Furthermore, the spawning potential ratio (SPR) remained 5%-7%（ =0.96,1.03 and 1.11 year）. On the whole, both of growth and recruitment overfishing were found on this stock and required to reduce the fishing effort. The results of stock assessment may explain the trend of decreased yield in the recent years.