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

Abstract

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.