Albacore (Thunnus alalunga) CPUE Trend from Indian Core Albacore Areas based on Taiwanese longline catch and effort statistics dating from 1980 to 2013 (Draft: July 12, 2014)

SUMMARY Because of disharmonious CPUE trends, using generalized linear models without the effect of fishing gears interventions, were observed during recent assessments on Indian Ocean albacore, an attempt of identification the‘Core albacore Area’ was recommended to rectify this problem. This study was thus to propose the‘Core albacore Area’ and to standardize its corresponding albacore abundance indices based on Taiwanese longline fisheries data series. Two areas were proposed by Taiwan as the core albacore area, namely South area 2a (S15°-45°, E55° -100°) and South area 2b (S20°-40°, E20°-70°) respectively. For Taiwanese longline fishery, both proposed core areas do have own characteristics and represented meaning. South area 2a is always the most dominate fishing ground of albacore by Taiwanese longline fishery. Although South area 2b is also an important fishing ground of albacore, it reflects the shift of fishing composition since 2000. Standardized yearly and quarterly CPUE series of albacore in both areas, dating from 1980 to 2013, based on Taiwanese longline catch and effort statistics by using Generalized Liner Model (GLM) procedure were carried out in present study. In South area 2a, the standardized yearly CPUE series showed a decline trend from early 1980s to early 1990s, after that there were two times increase sharply in 1990s, then leveled off since 1999 up to 2013. The standardized quarterly CPUE series showed a similar trend as those of obtained in the yearly trend but having more fluctuations. The results of ANOVA indicated that (1) both of yearly model and quarter-series model are statistically significant (P < 0.0001); (2) the factor of subarea in both yearly and quarter-series model is non significant, it may be because albacore is the most dominant targeting species in this area and this area just covered little subarea 4 caused; (3) comparatively, factors of yellowfin tuna and bigeye tuna play the important roles in explanation of its variation to the total. In South area 2b, the standardized yearly CPUE series indicated that it appeared a decline trend from early 1980s to early 1990s, then leveled off since early 1990s up to 2013 and a periodic up and down was presented as a cycle of 4-7 years. The standardized quarterly CPUE series showed a similar trend as those of obtained in the yearly trend but having more fluctuations. The results of ANOVA indicated that (1) both of yearly model and quarter-series model are statistically significant (P < 0.0001); (2) factors subarea and bycatch effect of OTHER have the most important effect; (3) the factor of quarter is non significant.