博士 / 國立臺灣海洋大學 / 環境生物與漁業科學學系 / 97 / Swordtip squid (Uroteuthis (Photololigo) edulis) is one of the main target species of torch-light fishery in the shelf waters off northeastern Taiwan. In the recent 50 years, the fishing intensity gradually increased and reached to the historic highest about 20,000 mt in 1998. But thereafter the catch kept to about 10,000 mt between 1999 and 2005, and even less than a quarter of that in 1998 (4853 mt) in 2007. The sharp decrease of catch took attention from people who were in industry, government and academic to start noticing the stock of swordtip squid. For the fishery management, it is needed to understand the reproduction, age and growth of swordtip squid, however, these important parameters are not studied systematically yet. As a consequence, we collected biological samples during the six years from 2003 to 2008, and analyzed statistically by using the Geographical Information System to understand the population structure, reproduction strategies, age, and growth of swordtip squid. The results obtained are summarized as follow:
The monthly variations of GSI (Gonadosomatic index), percentage of mature squid, and monthly hatched frequency during the period of 2003 to 2008 indicated that swordtip squid spawned in spring and autumn. ML (dorsal mantle length), BW (body weight), and GW (gonad weight) of spawning groups in autumn were larger than in spring. Gonad development was also well-rounded in autumn. The male ML at 50% maturation in spring and autumn spawning groups were 139 mm and 159 mm respectively, and female were 163 mm and 199 mm respectively. The distributions of GSI and the percentage of matured squids therefore suggested that the coastal water off northern Taiwan between 25?N and 26.5?N, 121.5?E and 122.5?E was probably the spawning ground of swordtip squid in spring and autumn.
The growth curve of swordtip squid is fitted by the exponential model based on statoliths daily growth increments of the squid and its ML and BW. The maximum age observed is 271 days in female and 253 days in male, an evidence showing that swordtip squid has a lifespan of about 9 months in both sexes. According to the analysis of the growth rates (DGR and G), it is showed that the male grew faster than female when the swordtip squid was older than 220 days, meanwhile the growth in both sexes reached the fastest rate of 4.5 mm/day or 7 g/day. We also compared the growth conditions of same age swordtip squid in the shelf waters off northeastern Taiwan and in southern waters of Japan. It is noticed that the growth of the former is faster than that of the latter. Based on monthly hatched frequency in both sexes of squid, they were mainly hatched in spring and autumn seasons, althought they sometimes hatched in winter. To compare the difference of growth rate in spring and autumn hatched groups, it is showed that no obvious difference of growth between two groups of squid while they are in the age younger than 180 days old. In contrast, the growth of autumn-hatched squid was faster than spring-hatched squid after they reach the age of 180 days old. The faster growth rate of autumn-hatched squid might due to the water temperature gradually increases 6 month after their hatching; in contrast, the water temperature gradually reduces while the spring-hatched squid are 6 month old.
The shelf water off northeastern Taiwan was linked to the seasonal changes of the Kuroshio Current and the Mainland China Coastal Current and the topographic features, which caused the suitable habitat of the swordtip squid. Swordtip squid distributes mainly along the coastal water, upwelling area, and frontal area. Through the results of ML and mature stage frequencies, it is showed that more mature female and male squids present in the coastal water and upwelling area during spring and autumn spawning period. It is suggested that the coastal and upwelling regions might be the spawning grounds. Additionally, the frontal area was used to catch small and immature squid. We suggested that it is feeding ground for the growth of squid. Squid only distributes in the coastal water and upwelling area during Janruary to March every year. Because the mean ML was smallest than other months, we consider that the frontal area should be the nursery ground, too.
| Identifer | oai:union.ndltd.org:TW/097NTOU5451026 |
| Date | January 2009 |
| Creators | Kae-Yih Wang, 王凱毅 |
| Contributors | Kuo-Tien Lee, 李國添 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 114 |
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