碩士 / 國立高雄海洋科技大學 / 漁業生產與管理研究所 / 95 / Many studies indicated that a conversion from J-style hook to circle hook might reduce the fishing mortality in tuna longline fishery. But the effects of this change on catch rate of target species were still unclear. To evaluate the effects, we carried out 31 sets of comparative fishing test from 26 April, 2006 to 06 June, 2006 by using a commercial vessel operated in the eastern Pacific Ocean. This study tried to compare the fishing effects on any caught species between using two sizes of traditional tuna hooks (standard Taiwan hook sizes：3.4 and 4.2 inch) and two sizes of circle hooks (size 4.0 and 4.2 inch). Also the bathythermographs were used to record the temperature-depth data during experiments. The suggestions obtained from results are as follows:
(1) After the soak time of each type of hook was standardized, catch rates of both Circle hook types (size 4.0 inch and 4.2 inch) for any fishing species had no significant difference (P>0.05). Catch rates for billfishes between using Circle hook (size 4.2 inch) and J-style hook ( size 4.2 inch) has significant difference (P<0.05) while catch rates for other fishing species had no significant difference(P>0.05) between them.
(2) All types of hook were more likely to lodge in the mouth for tuna and skipjack species, but other fishing species were more likely to be hooked in the internal position. The possibility of hook lodged in the mouth for any fishing species among using any hook type had no significant difference (P>0.05). It also showed a higher survival rate by using either small hooks (3.4 and 4.2 inch J-style hook) or circle hooks (4.2 inch of Circle and J-style hook).
(3) The body lengths of captured bigeye tuna between all hook types were not significant difference (P>0.05). But the body length of yellowfin tuna caught by 3.4 inch J-style hook had longer than those caught by 4.2 inch J-style hook (P<0.05), and it caught by 4.2 inch Circle hook had also longer than those caught by 4.2 inch J-style hook (P<0.01).
In this study, the results indicated that a change from 4.2 inch J-style hook to 4.2 inch Circle hook had no significant impact on fishing rates. Furthermore, usage of circle hooks instead of conventional tuna hooks could increase the fishing length for tunas and survival rate at haulback. Therefore, promotion of using circle hook could be extended from offering the training course for fishers in Taiwan tuna longline fishery, and would conform to the trend of international conservation.
| Identifer | oai:union.ndltd.org:TW/095NKIM8451008 |
| Date | January 2007 |
| Creators | Lin, Hsin-Jung, 林新榮 |
| Contributors | Chen, Chao-Ching, 陳朝清 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 103 |
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