Preliminary standardized catch rate of silky sharks caught by Taiwanese large-scale longline fishery in the Indian Ocean

The silky shark catch and effort data from the logbook data of Taiwanese large longline fishing vessels operating in the Indian Ocean from 2005-2018 were analyzed. Based on the effort distribution, four areas, namely, A (north of 10ºS, east to 70ºE), B (north of 10ºS, 70ºE-120ºE), C (south of 10ºS, 20ºE-60ºE), D (south of 10ºS, 60ºE-120ºE) were categorized. Due to the large percentage of zero shark catch, the catch per unit effort (CPUE) of silky shark, as the number of fish caught per 1,000 hooks, was standardized using zero-inflated negative binomial model (ZINB) that allows for “extra” zeros. ZINB model includes the main variables year, quarter, area, hooks per basket (HPB), and CTNO. The standardized CPUE showed a stable trend for silky sharks from 2005 to 2014 and increased steadily thereafter with peaks in 2014. The results obtained in this study can be improved if longer time series logbook data are available.