Cpue Standardisation for Bigeye and Yellowfin Tuna in the Western and Central Pacific Ocean

Executive summary Indices of catch per unit effort are presented for bigeye and yellowfin tuna in the WCPO from 1952 to 2009, based on analyses of aggregated Japanese distant water longline data. One change was made to the methods for estimating indices of abundance for the bigeye and yellowfin stock assessments, with removal of the targeting indicator based on CPUE of other species. This change had little effect on the CPUE trends. An alternative CPUE trend for a subset of region 3 was estimated based on the area south of 10N. The trend for this sub-regional model was more optimistic in recent years. The full region 3 series may be biased by significant albacore-targeted effort in the north since 1995, so an index based on the southern region may be more reliable. Both the bigeye and yellowfin indices may be affected by increasing targeting of bigeye tuna in recent years.