| 英文摘要 |
In this study, catch and effort data for blue marlin in the three oceans, swordfish and southern bluefin tunas in the Indian Ocean, and skipjack tuna in the Pacific Ocean were aggregated to analyze each CPUE (catch-per-unit-effort) trend for Taiwanese longline and purse seine fisheries. Indian swordfish stock status was evaluated using age-structured model.
Besides a brief review on the global blue marlin fishery condition by analyzing the fishery data of blue marlin in the three Oceans, the catch and effort data of blue marlin in the Japanese, Taiwanese, and Hawaiian tuna longline fisheries in the Pacific Ocean were collected and analyzed. The main fishing grounds of Japanese longline fleets were in the tropical areas of the Pacific Ocean and the waters off Japan and Australia, while the Taiwanese tuna longline fleets mainly operated in the South Pacific Ocean and the Hawaiian tuna longline fisheries in the waters around Hawaiian Islands. However, the maps of catch-rates indicated that the habitats of blue marlin mainly distributed in the tropical waters of the Pacific Ocean. The standardized CPUE (catch-per-unit-of-effort) trends for each region showed that the catch-rates of blue marlin are higher in the tropical waters than those in the temperate areas for the Japanese tuna longline fleets. However, the catch-rates of Japanese longliners in tropical waters of the Pacific Ocean were also higher than those of Taiwanese longliners operated in the same waters although there are some differences in the historical trends between these two fleets. The fishery data from Hawaiian tuna longline fleets showed a decreasing trend in recent years. We need to examine the results with more detailed information to further discover the potential differences among the longline fisheries catching blue marlin in the Pacific Ocean.
The global skipjack tuna fishery condition was also reviewed by analyzing the fishery data of skipjack tuna in the three Oceans. In addition, CPUE of Taiwanese distant-water tuna purse seine fishery for skipjack tuna in the Western and Central Pacific Ocean was standardized using the generalized linear model (GLM). The results indicated a stable stock condition in recent four years but with likely slightly decreasing trend since the year 2000. The stock condition should be continuously assessed and monitored carefully.
The age-structured assessment model without sex factor was conducted for evaluating the population status of the swordfish in the Indian Ocean. Based on the results of this study, the fleet-aggregated fishing intensity in 2006 was higher than that at which MSY is achieved and the spawning stock biomass in 2006 was about 40% of its unfished level and much higher that at which MSY is achieved. Therefore, the results of this study indicate that there is probable overfishing of the swordfish stock in the Indian Ocean in recent years while the stock currently appears not to be in an overfished state.
The trend of standardized CPUE of southern bluefin tuna caught by Taiwanese longline fishery during 2002 and 2006 was consistent with nominal CPUE, which increased gradually since 2003. However, no long term trend of CPUE is available because the data from 2002 to 2006 were only used in this study. In addition, the CPUE also calculated based the data of the “core vessels” which were sieved out based on the data from 2006 to 2007. The results indicated that the CPUEs calculated based on the data of all vessels were close to those based on the data of core vessels. |