碩士 / 國立臺灣海洋大學 / 環境生物與漁業科學學系 / 99 / Spotted mackerel, Scomber australasicus is the major species of mackerel-carangid fishery in the northeastern Taiwan. The gradual replacement of mackerel purse seine by tiger seine, a more efficient fishing gear, and oceanic climate change especially SST rising in the fishing ground are two impact factors to the fish stock in the recent two decades. In this study we analyze fish samples collected in two periods, 2001/2~2002/6 (period I) and 2009~2010/6 (period II) dominated by purse seine and tiger seine respectively, to find any clues of change in growth, maturity and reproduction through measurements of body length and weight, gonosomatic index (GSI), hepasomatic index (HSI) and gonad slice. The catch and effort data as well as the sea surface temperature data in the fishing ground were also analyzed to explain those adaptive changes found in biological samples. This study has following findings:
1.The relationship between length and weight for the two periods were significantly different, where samples in period II were heavier than those in period I under same body length. Meanwhile, the minimum size at maturity declined from 25 cm down to 24.7 cm, and size of 50% maturity also reduced from 30 cm to 28 cm, which indicate the growth and reproduction of spotted mackerel varied in the two periods.
2.The GSI values suggested that spawning behaviors in 2001 and 2010 were more active than the other two years. The monthly distribution of GSI further showed that spawning in 2001 were more concentrated with peak in March, however spawning period in 2010 were longer and extended to June. The SST in fishing ground during the two Periods played an important role. Higher SST and early warming in 2001 may cause relatively high GSI and concentrated spawning period. The longer spawning period may also linked to late warming in fishing ground.
3.There were two stages of relative biomass indices indicated by standardized catch per unit effort (CPUE) using general linear model during 1990~2010. The CPUE before 2000 were about 20~40 ton/day and declined dramatically to 11 ton/day after 2000. Such continuous decrease in fish stock may cause density dependent effect on increase of feeding capacity for individual fish and result lower minimum and 50% of maturity size.
4.The correlation coefficient between standardized CPUE and sea surface temperature (SST) implied that continuous SST rising in the fishing ground disadvantage to the stock. Early mature phenomenon is a major response of spotted mackerel to intense fishing pressure; meanwhile the SST rise in environment also plays an important role. As the fishing efficient of tiger seines is better the purse seines and SST rising trend are expected in the future, which should be carefully considered in the management of fisheries on spotted mackerel stock.
| Identifer | oai:union.ndltd.org:TW/099NTOU5451001 |
| Date | January 2011 |
| Creators | 蕭韵穎 |
| Contributors | Hsueh-Jung Lu, 呂學榮 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 86 |
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