Woodworth-Jefcoats et al.: Oceanographic variability, fishery expansion, and longline catches in the North Pacific 
231 
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Q1 
® Q2 
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O 03 
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SW 
CW 
NW 
NE 
15 
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18 
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11 
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SW 
CW 
NW 
NE 
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Percentage of annual effort 
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p' 
1995 2005 2015 
20 -13 -10 -5 0 5 
A Percentage 
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Figure 2 
The mean percentages of total annual effort that occurred in each quarter and region at 
the (A) beginning (1995-1997) and (B) end (2013-2015) of the time series from logbook 
data examined in this study of the Hawaii-based longline fishery. (C) The change in the 
percentage of total annual effort that occurred in each quarter and region is shaded in 
color and overlaid with the total annual effort set in each region and quarter in black. 
Four regions were used in these analyses: southwest (SW); central west (CW); northwest 
(NW); and northeast (NE). 
There was virtually no fishing effort in the SE region; 
therefore, it was not included in our analysis. 
Interannual variability In 1995, nearly all (97.1%) of the 
Hawaii-based longline effort occurred west of 150°W 
and south of 26°N in the CW and SW regions. Over 
time, the fishery expanded, and in 2015, 41.3% of the 
longline fishing effort occurred either north of 26°N or 
east of 150°W in the NW and NE regions. Total effort 
also increased; the total number of hooks set increased 
steadily from nearly 8.4 million in 1995 to over 47 mil¬ 
lion in 2015. This increase in fishing effort was great¬ 
est in the NE region (Fig. 2). Time series of total effort 
in each region and quarter (Fig. 2) show that effort 
increased in the CW and SW regions until about 2004. 
After this time, and with the exception of the CW re¬ 
gion in the first quarter, effort in these regions has 
remained roughly stable, whereas effort in the NW and 
NE regions increased steadily. 
Fishery expansion is detailed in Figure 2. It shows 
that, over the past 21 years, the geographic focus of 
the fishery changed substantially. Across all quarters, 
the proportion of total annual effort in the SW and CW 
regions declined by about 1-8%. At the same time, the 
proportion of total annual effort in both northern re¬ 
gions increased by 2-13%, with a strong maximum in 
the NE region during the third quarter (13% versus 
7%, the next closest value). 
International competition The ratio of Hawaii-based ef¬ 
fort to international effort varied by region (Suppl. Fig. 
2) (online only). Hawaii-based effort accounted for nearly 
all effort recorded in the CW region; there was little 
to no competition from international fisheries. For the 
grid cells in the SW region with Hawaii-based fishing 
effort, international fisheries’ effort was roughly equal 
to the effort of the Hawaii-based fishery. However, the 
ratio of Hawaii-based effort to international effort has 
increased steadily in the first quarter of each year over 
the years studied. For grid cells in the NW region with 
Hawaii-based fishing effort, there was little competi¬ 
tion from international fisheries during the second and 
third quarters. In the first and fourth quarters, the ra¬ 
tio of Hawaii-based fishing effort to international effort 
has increased over the past decade, and the efforts of 
the 2 groups are now roughly equal. With the exception 
of the first and fourth quarters during the first 5 years 
of the time series, there was virtually no international 
fishing effort in the NE region. 
Oceanographic variability 
Spatial variability A great deal of spatial variability 
across the fishing grounds was observed in the median 
depth and vertical extent of the preferred thermal hab¬ 
itat of bigeye tuna (8-14°C) (Fig. IB). Median thermal 
habitat depth was at its maximum in the CW region, 
about 350-400 m below the surface, and it was shal¬ 
lowest in the NE region where it occurred within about 
300 m of the surface. In the SW and NW regions, me¬ 
dian thermal habitat depth ranged from 400 m to the 
surface at the northernmost latitudes. The full vertical 
extent of preferred thermal habitat of bigeye tuna also 
varied by region (Suppl. Fig. 3) (online only). The extent 
of this habitat was greatest in the SW and NW regions 
(depth: 200-450 m), least in the CW region (depth: 
