| 英文摘要 |
Annual ratios in catch of sailfish to spearfish were estimated using the observer data collected from ICCAT database and Taiwanese longline fisheries in the Atlantic Ocean. Based on the ratios, historical catches and abundance indices were developed and analyzed for sailfish. Results showed that two peaks occurred for the catch of sailfish during the late 1960s and the early 1990s. The abundance indices of sailfish decreased year by year after an extremely increase in the early 1990s. However, abundance indices of sailfish remained relative stable for the western stock in recent years (1999-2007), but obviously increased for the eastern stock during recent years (2004-2007).
???? Based on the two scenarios of spatial structure for swordfish stock in the North Pacific Ocean, an age-structured population dynamics model was fitted to catch, catch-rate, and length-frequency data for the main swordfish fisheries (Japanese, Taiwanese, and Hawaiian longline fleets) to examine the current status of the swordfish population in the North Pacific Ocean. Results indicate that the current spawning stock biomass (2006) was at a high fraction of its unfished level and that the current fishing intensity (2006) was less than FMSY for different scenarios of stock structure of swordfish. Therefore, the swordfish stock in the North Pacific Ocean appears to be relatively stable at the current level of exploitation.
???? Catch and effort data of skipjack tuna in WCPO from 1983 to 2008 were used to evaluate spatial and temporal dynamics of skipjack tuna’s CPUE and the gravity of fishing. The results suggested that the distributions of skipjack tuna population and purse seine fleets in WCPO were correlated to the variation of environmental factors (e.g., sea surface temperature, SST). This study validated the effect of ENSO on the distribution of skipjack tuna population, and suggested that 29 Co isotherm is a good proxy for evaluating the effect of ENSO on skipjack tuna’s distribution. Standardized catch rates of skipjack tuna for the Taiwanese purse seiners in WCPO was evaluated by applying two alternative modeling approaches (GLM and GAM). All the main effects (i.e., year, month, latitude, longitude, school type and CPUE of yellowfin tuna), except for Area for GLM analysis, were significant. Generally, the standardized CPUE is robust to the choice of the analytical framework, and suggests that standardized CPUE was relative low before year 1990, increased to the peak in year 1996, and then smoothly decreased to a stable level of 20 mt/day fished in the past decade.
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