228 
National Marine 
Fisheries Service 
NOAA 
Abstract—The fishing grounds of 
the Hawaii-based longline fleet span 
over 13 million km 2 in the central 
North Pacific Ocean. We investi¬ 
gated over 20 years of commercial 
fishery logbook data and indepen¬ 
dent observer data to gain an under¬ 
standing of the variation in magni¬ 
tude and composition of the fleet’s 
catch on both intra- and interan¬ 
nual scales. We found that the fish¬ 
ery follows a quarterly geographic 
migration and that the fishery has 
expanded over time with a 5-fold in¬ 
crease in effort and a spatial expan¬ 
sion primarily to the northeast of 
Hawaii during the third quarter of 
the year. The World Ocean Atlas and 
ocean reanalysis data indicate that 
waters to the northeast of Hawaii 
are a particularly effective fishing 
ground because of the vertical over¬ 
lap of preferred thermal habitat and 
fishing gear. Furthermore, we found 
that the Hawaii-based fleet faced lit¬ 
tle international competition in this 
region. The expansion of the fishery 
has also affected catch composition, 
resulting in discard rates that ex¬ 
ceed target catch rates. Understand¬ 
ing how catch varies as a result of 
oceanographic variability and fleet 
movement can lead to a more ef¬ 
ficient, resilient, and cost-effective 
fishery. 
Manuscript submitted 6 July 2017. 
Manuscript accepted 12 April 2018. 
Fish. Bull. 116:228-239 (2018). 
Online publication date: 24 May 2018. 
doi: 10.7755/FB.116.3-4.2. 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Bulletin 
fb- established in 1881 •&. 
Spencer F. Baird 
First U S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Synergy among oceanographic variability^ 
fishery expansion, and longline catch 
composition in the central North Pacific Ocean 
Phoebe A. Woodworth-iefcoats (contact author ) 1 ' 2 
Jeffrey J. Polovina 1 
Jeffrey C. Drazen 2 
Email address for contact author: phoebe.woodworth-jefcoats@noaa.gov 
1 Ecosystem Sciences Division 
Pacific Islands Fisheries Science Center 
National Marine Fisheries Service, NOAA 
1845 Wasp Boulevard, Building 176 
Honolulu, Hawaii 96818 
2 Department of Oceanography 
School of Ocean and Earth Science and Technology 
University of Hawaii at Manoa 
1000 Pope Road 
Marine Science Building 
Honolulu, Hawaii 96822 
The Hawaii-based longline fishery is 
among the most economically valu¬ 
able fisheries in the United States, 
ranked 6 th in 2015 (NMFS 1 ). Its 
footprint spans over 13 million km 2 
in the central North Pacific Ocean, 
ranging from the dateline to 120°W 
and from equatorial waters to rough¬ 
ly 40°N. The Hawaii-based longline 
fleet includes 2 fisheries: a shallow- 
set fishery targeting swordfish (Xi- 
phias gladius) and a deep-set fishery 
targeting bigeye tuna (Thunnus obe- 
sus). The deep-set fishery is the dom¬ 
inant fishery; both effort and catch 
(magnitude and value) are an order 
of magnitude greater than that of 
the shallow-set fishery (NMFS 2 ). For 
1 NMFS (National Marine Fisheries Ser¬ 
vice). 2016. Total commercial fish¬ 
ery landings at major U.S. ports sum¬ 
marized by year and ranked by dollar 
value. Fisheries Statistics Division, 
NMFS. [Data available at w ebsite, ac¬ 
cessed October 2016.1 
2 NMFS (National Marine Fisheries Ser¬ 
vice). 2016. Annual commercial land¬ 
ing statistics. Fisheries Statistics Divi- 
this reason, we focused on the deep- 
set fishery in our study. 
The deep-set fishery operates 
largely during the day (Bigelow et 
al., 2006). Hooks are primarily set 
between 100 and 400 m below the 
surface, and the median hook depth 
is 250 m (Boggs, 1992; Bigelow et 
al., 2006). This depth range coincides 
with the daytime vertical habitat of 
bigeye tuna; tagging data indicate 
that fish of this species spend much 
of the day 200-400 m below the sur¬ 
face (Boggs, 1992; Ward and Myers, 
2005a; Howell et al., 2010) in waters 
with a temperature range of 8-14°C 
(Howell et al., 2010) and oxygen con¬ 
centrations over 1.0 mL/L (Boggs, 
1992; Lehodey et al., 2010). 
Although bigeye tuna are the tar¬ 
get of the deep-set fishery, the catch 
also includes a number of other spe¬ 
cies, some of which are also of com¬ 
mercial value. These commercially 
valuable, nontarget species include 
sion, NMFS. [Data available from web¬ 
site, accessed October 2016.1 
