144 
Fishery Bulletin 120(2) 
ae 
Proportion of species caught 
Bigeye Pacific opah 
| Smalleye Pacific opah 
N 
2000 km ® 
0 1000 
160°W 
140°W 120°W 
Figure 3 
The proportions of genetically confirmed bigeye Pacific opah (Lampris megalopsis) and smalleye 
Pacific opah (L. incognitus) caught in the deep-set pelagic longline fishery for 5°-by-5° blocks in the 
eastern North Pacific Ocean during 2009, 2010, 2017, and 2018. In each block, the top-left number 
refers to the total number of trips by fishing vessels during which opah used for genetic analysis 
were caught, and the top-right number refers to the total number of opah caught on those trips. 
Blocks with data for less than 3 vessels are not shown to maintain confidentiality. 
bigeye Pacific opah in 2014-2018 but remained fairly con- 
sistent in mixed areas. Because of the low effort in the 
eastern region during 1996-2013, it was not possible to 
compare CPUE across periods. It is apparent, however, 
that the CPUE in the region dominated by smalleye Pacific 
opah during 2014-2018 was consistently higher than in 
the regions dominated by bigeye Pacific opah and in the 
mixed area across both periods. Table 2 also highlights 
that the majority of fishing activity in this region has 
occurred since 2014. 
Discussion 
The results of this study, linking fisheries data with more 
detailed information on the distribution of bigeye Pacific 
opah and smalleye Pacific opah, advance our understand- 
ing in important ways. First, our analyses allowed exam- 
ination of shifts in fisheries interactions in the context of 
opah distribution. Second, the results of this work provide 
a more complete picture of the range of the 2 species and 
insight into temporal and spatial patterns in catch in a 
species-specific context. This study represents an import- 
ant step toward understanding the basic biology and 
fisheries interactions of the 2 opah species in the eastern 
North Pacific Ocean. 
Fisheries distribution and catch per unit of effort 
The effort and spatial distribution of both the US. 
pelagic longline fleets targeting bigeye tuna and sword- 
fish in the Pacific Ocean have changed from 1996 to 
2018. In the shallow-set fishery, the range and effort 
decreased. In contrast, the deep-set fishery increased in 
both effort and range, with substantially more effort 
east of 140°W. Although observations of these shifts in 
fisheries are not new (Woodworth-Jefcoats et al., 2018), 
it is important to understand the dynamics of the fish- 
ery in the context of interactions with opah. Total effort 
has increased in the region where the overall CPUE 
and proportion of smalleye Pacific opah are higher. In 
addition, effort has shifted from shallow-set gear to 
deep-set gear, and CPUE of opah is also higher in the 
deep-set fishery than in the shallow-set fishery. These 
findings are consistent with the increase in landings of 
opah in the deep-set longline fishery (National Marine 
Fisheries Service, Office of Science and Technology, 
commercial fisheries landings, available from website, 
accessed May 2020). However, variable fishing foot- 
prints, the limit of evaluation to only 2 periods, and 
multiple regulatory shifts make direct temporal com- 
parisons of CPUE and effort challenging. The relative 
contribution of the 2 species to this increase in landings 
