CPUE standardization of yellowfin tuna caught by Korean tuna longline fishery in the Indian Ocean, 1977-2017

In this study, CPUE (catch per unit effort) standardization for yellowfin tuna of Korean longline fishery in the Indian Ocean was conducted by Generalized Linear Model (GLM) using operational (set by set) data 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. Yellowfin tuna CPUE by Korean tuna longline fishery was standardized for the whole, west and east areas. The standardized CPUE trends were different between west area and east area. The standardized CPUE for whole area was about 7.8 in 1977, and showed sharply decreased after that. During 1980s it showed a level of 3-4, but again decreased thereafter, and since the mid-1990s it showed the steady trend with a level of about 1.0. The standardized CPUE for west area showed a similar trend with those of whole area, but showed the large increasing in 2003-2005 and 2013. However, the standardized CPUE for east area had decreased since 1977, and is showing the low level of below 1.0 in recent years.