A study on Southern Bluefin Tuna longline fishing condition in relation to ocean temperature fluctuation in the Central Indian Ocean

• Main Authors: Shu-Chen Kao, 高淑真
• Other Authors: Hsueh-Jung Lu
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/p94q64

碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 94 === In this study, we collected in-situ data to analyze fishing condition, including hook rate, hook depth and ambient temperature of the longliners seasonally targeting southern bluefin tuna (SBT) in the Central Indian Ocean (CIO). We also compiled the SBT historical catch and effort data to compute standardized CPUE series (1982~2003) using General Linear Model, then compared with sea surface temperature (SST) in the same period to understand the relationship among fishing, oceanic and environmental condition in the CIO. The principal results are as follow. 1. According to the records of TDRs collected in CIO during 2004/2005 fishing period, about 80% of the deployed hooks spread between 50~175 m where average ambient temperature were around 14~19.4 °C. The high hook rate region were located between Subtropical Convergence Zone (STCZ) and Subantarctic Convergence Zone (SACZ) with 15~20 °C in SST and 14~17 °C in depth of 50~175 m, where vertical temperature variation is moderate from surface to 200 m in depth. 2. Both standardized CPUE indices of SBT in quarters 2 and 3, the major fishing seasons, showed rising trends during 1992-1996. However, during the remaining years, the CPUE in the 2nd quarter were at low level. The CPUE of the 3rd quarter decreased slightly after 1997, but relative higher than that of the 2nd quarter, indicating more concentrated fishing seasons developed in the recent years. 3. There were significant negative correlation found between standardized CPUE and large-scale SST throughout the year, especially in quarters 2 and 3. The negative correlation regions were mostly concentrated in western CIO during the 2nd quarter, then move to central CIO where fishing operations took place in the 3rd quarter. 4. Comparing the trends observed among the standardized CPUE, SST and Southern Oscillation Index, we obtained that the SST fluctuation almost synchronized the ENSO signal in the tropical waters (0~20 °S). However the SST variations in higher latitudes (30~50 °S) showed slower and longer tempo. The CPUE of SBT in the CIO seemed to vary out of phase with SST oscillations in the mid latitudes around 30~50 °S. According to results from the in-situ and historical fishing data, we can ascertain that SBT CPUE will conversely vary with SST. An even stronger phenomenon also observed from the CPUE of Japanese longliners operating in the regions south to the CIO (CCSBT Zone 8). The fluctuation of SBT CPUE in the CIO fishing ground is probably linked to the expansion of cold water mass in the Southern Ocean. We speculate that the cycles of such expansion are linked to by Antartic Current Wave.