CPUE standardization for bigeye tuna caught by Korean tuna longline fisheries in the Indian Ocean

In this study, bigeye tuna CPUE (catch per unit effort) standardization of Korean longline fisheries in the Indian Ocean was conducted by Generalized Linear Model (GLM) using operational data and aggregated data (1977-2012) to assess the proxy of the abundance index. The data used for GLM were catch (in number), effort (number of hooks) and number of hooks between floats (HBF) by year, month and area. In addition, we explored the core area where Korean tuna longline vessels have been mainly fishing for bigeye tuna. Bigeye tuna CPUE was standardized for the whole area using both operational data and aggregated data and for the core area. All the CPUEs had decreased until the early of 2000s except a jump in the mid-1990s, and then showed a steady trend with a level of 2-3 in recent years.