An analysis on catch composition changes of gill net fishery in Kong-Liao Region

• Main Authors: Yi-Shun Cheng, 鄭逸姍
• Other Authors: Kuan-Yung-Hsieng
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/60066236012162848579

碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 99 === This research is based on the investigations for gill net fishery in Gongliao from 1995 to 2010 by 3 fishery-approch ecosystem indices, Mean trophic level (MTL), Contribute trophic level (CTL) and Fishing-in-Balance (FiB), to analyze the long-term utilization of gill net fishery in Gongliao. In addition to discuss the long-term shift of seasonality for migratory species, we use ratio-to-moving-average method to calculate Season Index (SI), and examine seasonality by ANOVA, then we analyzed the composite seasonality changes hidden in the landing data. The results of this study are as following: (1)The MTL for fish caught by gill net in Gongliao during 1995~2010 shows the decreased annually in 1995~1998, then increased and reached the peak in 2005, then decreased gradually. (2)We use the data in 1995 as the model, FiB index undulated between -0.8~+0.5, in 2005 it reached the high peak and then went down annually. (3)The catches and CTL in Gongliao during 1995~2010 indicates that Aluterus monoceros (TL=3.51) is the highest contributor to MTL, followed by Mugil cephalus (TL=2.13), Seriola dumerili (TL=4.5), and Prionurus scalprum (TL=2.0) (4)According to the determined seasonality of fish, spring/winter migratory species comprised about 34.2% of annual catch with the highest value of 72.57% in 2005. The gradual increase trend of summer/autumn to spring /winter catch ratios may imply a weakened strength of winter migratory species. (5)The catches by gill net won’t effect by season shifting, plus the geography condition (half-closed sea bay), the species of reef fish would be the main catch by gill net. The determined seasonality shows the species combination of catch will have no effects by the appearing of migratory species.