| Summary: | 碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 102 === Chub mackerel (Scomber japonicus) is a straddling fish stock commonly utilized by Taiwan, China, Japan, Korea and etc. The Taiwanese purse seine developed rapidly in recent years and there has been an increasing trend in the proportion of chub mackerel catch in the mean time. However, the basic data of chub mackerel is too old and rare to compare with other interested countries for fishery management. Therefore, we carried out the present reproductive biology study for chub mackerel in the northeastern Taiwan.
We collected chub mackerel samples monthly from the catch in the northeastern waters off Taiwan during July, 2012- July, 2013. A total of 2,474 valid samples were used in this study, including 1,110 females, 960 males and 404 sex-unknown. These samples were used to conduct reproduction, maturation, growth and age analysis for the stock. The major results were summarized as follow:
1. The Gonosomatic Index (GSI) indicated that spawning period of chub mackerel were between January and May. Mean while, the gonad histology indicated that the female chub mackerel reached a high maturity rate in April, which implied that the spawning period, peaked around that time.
2. The minimum fork length of mature was found about 20 cm and the fork length of 50% mature was at 32.3 cm. The mean fecundity in all stages was 102,467±44,369 oocytes. However, the fecundity in ripe egg stage ranged from 44,910 to 226,991 oocytes and egg diameter ranged from 0.4 to 0.6 mm.
3. According to the age determination by otolith, the oldest sample was 6-year-old (FL=39.7cm). A von Bertalanffy growth equation (L∞=40.9 cm, k=0.47 yr-1, t0= -0.32 yr) were obtained to estimate the age composition of the chub mackerel catch. The age of chub mackerel caught by Taiwanese seines in the study area were mostly in age-1 and age-0, comprising 51.8% and 33.1% of the total catch, respectively.
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