| 英文摘要 |
The fishery data and catch information of Taiwanese longline fleets in the Pacific and Atlantic Ocean were obtained from the OFDC for 1964-2009 and 1967-2009 respectively. The catch and effort data were standardized for the North Pacific swordfish, Pacific striped marlin, and Pacific and Atlantic blue marlin to examine the trends of the relative abundance index for these species. We assessed the current status of North Pacific swordfish stock and converted the catch-at-length data of blue marlin caught by the Taiwanese longline fleets in the Atlantic Ocean into catch-at-age using the age-length key. Year, month, latitude and longitude effects were all statistically significant (p ＜ 0.01) in the CPUE standardization. The catch-rates of North Pacific swordfish showed an increasing trend and maintained at relative higher level after 2000, with increasing trend for the last three years. The CPUE of Pacific blue marlin stabilized after 1980, but increased since the late 1990s and decreased in recent years. The CPUE trends of Atlantic blue marlin caught by Taiwanese longline fleets were much similar between single-stock and two-stock scenarios. The catch-rates of blue marlin decreased rapidly in the early 1970s, and appeared stable thereafter until present. The striped marlin CPUE in the Pacific Ocean is quite stable generally, but increased after 2000 and decreased recently. The sizes of blue marlin caught by Taiwanese longline fleets in the Atlantic Ocean ranged from 100 to 300 cm, and contributed to a bi-mode in the length-frequency distribution for several years. Blue marlin is a sexual dimorphic species both in size and growth. As shown by the analysis using an age-length key, most of the blue marlin caught by Taiwanese fleets are larger than 3-5 years, but with large year variation in the age composition of blue marlin.
? |