Cooper et al.: Spatiotemporal catch patterns and population distributions of Lampris megalopsis and L. incognitus 145 
40°N; A 
30°N; 
20°N} 
10°N; 
i — i | N 
0°! 01000 2000km aN 
180° 160°W 140°W 120°W 
Proportion of 
bigeye Pacific 
opah 
1.00 
al 
mn 0.75 
30°Nj 
20°N} 
10°N; 
0° ‘ 0 1000 = 2000 km 
180° 160°W 140°W 
40°N! C 
30°N; 
20°N; 
10°N; 
0°! ; 0 1000 2000km 
180° 160°W 140°W 120°W 
Figure 4 
Contour maps of expected proportions of bigeye Pacific opah (Lampris megalop- 
sis) caught during 2009, 2010, 2017, and 2018 in the eastern North Pacific Ocean 
in the deep-set pelagic longline fishery, generated by using generalized additive 
models with (A) 4 (low), (B) 6 (medium), and (C) 8 (high) knots for the isotropic 
thin-plate regression spline. Areas with expected proportions of bigeye Pacific 
opah of 20.7 (darker blue area), <0.3 (darker red area), and 0.3-0.7 are classi- 
fied as dominated by bigeye Pacific opah, dominated by smalleye Pacific opah 
(L. incognitus), and mixed areas (no dominance), respectively. Bold contours indi- 
cate proportions of 0.7 and 0.3 to visualize the classification thresholds. 
Spatial distributions of species 
Paired with data from Hyde et al. (2014), 
the results of the additional genetic 
analyses in this study have filled the gap 
east of 140°W, outside of the U.S. exclu- 
sive economic zone, providing a more 
spatially complete picture of the distri- 
butions of bigeye and smalleye Pacific 
opah. Results of our evaluation of spe- 
cies distribution indicate that, during 
2009-2019, bigeye Pacific opah occurred 
throughout the region and smalleye 
Pacific opah occurred predominantly in 
the eastern and northern boundaries of 
the range of longline fisheries, with pro- 
portional abundance decreasing toward 
the west. There was no defined boundary 
between the distributions of the 2 spe- 
cies within the geographic scope of this 
study. South of 25°N, the approximate 
location of the North Pacific Transition 
Zone (Roden, 1991; Polovina et al., 2001), 
the transition from blocks dominated by 
smalleye Pacific opah to blocks domi- 
nated by bigeye Pacific opah occurred 
approximately between 140°W and 130°W. 
With the addition of new genetic sam- 
ples collected for our study, the delinea- 
tion of the species between 140°W and 
130°W is less defined than the distri- 
butions indicated by results from Hyde 
et al. (2014), who reported that a num- 
ber of the eastern blocks were all dom- 
inated by smalleye Pacific opah. In the 
North Pacific Transition Zone, the tran- 
sition was even less well-defined, and 
smalleye Pacific opah occurred across 
our entire study area. Additional genetic 
samples from this region would allow 
expansion of the model into the North 
Pacific Transition Zone in future stud- 
ies. The considerable overlap between 
the distributions of the 2 opah species 
could complicate retroactive examina- 
tion of species-specific trends. 
Although this study was confined to the 
approximate spatial extent of the US. 
pelagic longline fisheries in the North 
Pacific Ocean, data are available for 
regions outside this area and provide 
additional insight into the broader range 
of the 2 opah species in the Pacific Ocean. 
Results from genetic analyses of samples 
from the western Pacific Ocean near 
Japan and the southcentral Pacific Ocean 
cannot be calculated because of the lack of species- near America Samoa indicate that 100% of samples are big- 
specific landings data, and estimation of the relative eye Pacific opah (Hyde et al., 2014), indicating that the dom- 
contributions is beyond the scope of this paper. inance of bigeye Pacific opah continues both west and south 
