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CPUE standardization of blue marlin (Makaira mazara) caught by Taiwanese longline fishery in the Indian Ocean for 1995 to 2011









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    CPUE standardization of striped marlin (Kajikia audax) caught by Taiwanese longline fishery in the Indian Ocean for 1995 to 2011 2013
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    This study provided a CPUE standardization of striped marlin (Kajikia audax) caught by the Taiwanese longline fishery in the Indian Ocean for time periods of 1980-2011 and 1995-2011. The delta-lognormal GLM model is adopted to perform the CPUE standardization alysis since blue marlin is caught by Taiwanese longline fleet as bycatch species and large amount of zero catches are recorded in the operatiol data sets. The results indicate that the influence of incorporating environmental effects on CP UE standardization is not significant for striped marlin in the Indian Ocean. The CPUEs in Area MONS and Coastal area revealed similar trends and they substantially decreased since 1980 although the CPUE obviously fluctuated in early years. The CPUE in Area ISSG fluctuated before 1990, substantially increased between 1990 and 1995, and sharply decreased thereafter. In recent years, CPUEs obviously increased for all three areas. The area-aggregated CPUE obviously fluctuated before 1995 and it rev ealed obvious and continuous decline trend thereafter, while it slightly increased in recent two years.
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    Correlations between environmental factors and CPUEs of blue marlin (Makaira mazara) and striped marlin (Kajikia audax) caught by Taiwanese longline fishery in the Indian Ocean 2013
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    This study investigated the correlations between environmental factors (Indian Oscillation Index, Dipole Mode Index, Southern Oscillation Index, sheer currents, amplitude of the shear current, thermocline depth, and temperature at depth of 15/55m and temperature gradient at depth of 15/55m) and nomil CPUEs of blue marlin and striped marlin caught by Taiwanese longline fishery in the Indian Ocean. The results clearly showed that there are significant cycle-patterns between CPUEs and most environm ental factors. In addition, this study also suggested the environmental factors with the time-lags for CPUE standardization alyses of blue and striped marlins in the Indian Ocean.
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    Japanese longline CPUE for yellowfin tuna in the Indian Ocean up to 2012 standardized by generalized linear model 2013
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    Japanese longline CPUE (quarterly and annual) for yellowfin tu in the main fishing ground and whole Indian Ocean, as well as CPUE in each area in each of five areas for SS3 and Multifan-CL, was standardized up to 2012 by GLM (CPUE-LogNormal error structured model). Number of hooks between float (NHF) and material of main line and branch line were applied in the model to standardize the change of the catch rate which has been derived by fishing gear configuration. In order to avoid the bias of CP UE trend which may be caused by critical decrease of effort in the northwestern Indian Ocean, scerios without Area 2 was also applied. Basically, two series of standardized CPUEs including and excluding Area2 showed similar trend. In the main fishing ground, CPUE continuously decreased from around 15 (a nomil scale) in early 1960s to around 5.0 in 1974, and was kept in same level until 1990 with jump to 12.0 in 1977. Thereafter, it declined to about 3.0 in 1994 and has been kept in a low level w ith fluctuation between about 2 and 3 until 2007. After that, the CPUE declined to historical low level, 1.18-1.58 during 2008-2012. As the declining trend in the resent years was detected in both models including and excluding Area 2, where the piracy activity has been increasing since 2007, the resent declining trend would be reflecting actual change in abundance rather than change in CPUE derived from shift of fishing ground and/or decreased effort caused by increased piracy activity. The tre nd of standardized CPUE for whole Indian Ocean was similar to that of main fishing ground. Quarterly CPUE trends for main and whole Indian Ocean were similar to that of annual CPUE. Trends of CPUEs were relatively similar among areas, i.e. large decline to middle 1970s, relatively stable until around 1991 and steadily declining thereafter. Applying LT5LN5 factor (five degree block) in the model showed relatively large effect on the CPUE trend for Area 3 and 4 in which the declining trend until a round 1990 was steeper in the model without LT5LN5. Then, the CPUE trend derived from the model with LT5LN5 caused relatively flat trend throughout period alyzed.

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