Spatiotemporal catch patterns and population distributions of bigeye Pacific opah (Lampris megalopsis) and smalleye Pacific opah (L. incognitus) in the eastern North Pacific Ocean

Opah (Lampris spp.) are commercially valuable, non-target fish that are regularly landed in pelagic longline fisheries in the central and eastern North Pacific Ocean. Genetic studies have confirmed 2 species in the region: bigeye Pacific opah (L. megalopsis) and smalleye Pacific opah (L. incognitus). Spatial distributions of each species are not well-defined, and little is known about species-specific catch distributions because the 2 species are difficult to distinguish visually. The objectives of this study were to characterize spatiotemporal patterns of opah landings by using catch per unit of effort (CPUE) from logbook and observer data, for the period 1995-2018, and genetics-based species identifications. Results from generalized additive models indicate that bigeye Pacific opah dominate west of 140 degrees W and that smalleye Pacific opah dominate waters east of 130 degrees W (dominance is defined as a proportion of catch >= 0.7). The deep-set pelagic longline fishery had higher opah CPUE than the shallow-set fishery across the geographic range of these fisheries. Opah CPUE increased from west to east on both longline gears, indicating higher overall opah CPUE in the eastern regions of both fisheries, primarily dominated by smalleye Pacific opah. Opah CPUE also increased over time as the Hawaii-based longline fisheries expanded eastward. The results of this study highlight the need for species-specific catch data and will inform management of opah species.