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Historical and recent Historical and recent estimates of the body-size estimates of the body-size
and abundanceand abundanceof pelagic species takenof pelagic species taken
by longlineby longline
Peter WardPeter WardRAM MyersRAM Myers
Dalhousie UniversityDalhousie UniversityEB WP-7EB WP-7
Changes in Changes in pelagic fish pelagic fish communitiescommunities• Comparison of Comparison of
1990s (Hawaii) and 1990s (Hawaii) and 1950s (POFI) 1950s (POFI) longline datalongline data
• Species Species compositioncomposition
• SizeSize• Catch ratesCatch rates
Change in index of massChange in index of mass
Bigeye tunaBigeye tuna
Silky sharkSilky shark
Yellowfin tunaYellowfin tuna
Blue sharkBlue shark
1950s1950s
50 0 50
1990s1990s
020
4060
8010
012
0
100 50 0 50 100
Mean weight (kg)Mean weight (kg)
Cpu
e (n
o./1
000
hook
s)C
pue
(no.
/100
0 ho
oks)
DataData
FeaturesFeatures• Non-target speciesNon-target species• Size of each fishSize of each fish• Hook numberHook number• Depth of each Depth of each
catchcatch• Soak time of each Soak time of each
catchcatch
1950s1950s:: 1950–1958,1950–1958, 880880 daysdays survey gridsurvey grid
1990s1990s:: 1994–2002,1994–2002, 505505 daysdays commercial fishingcommercial fishing
Study areaStudy area
HawaiiHawaii 1950s1950s1990s1990s
11 33 66 99 1212
MonthMonth
1950s1950s
1990s1990s
1950s1950s
1990s1990s
02:0002:00 04:0004:00 06:0006:00 08:0008:00
Deployment Deployment timetime
Soak time Soak time (hr)(hr)
1950s1950s
1990s1990s
00 22 44 66 88 1010 1212 1414
00 100100 200200 300300 400400 500500 600600
1950s1950s
1990s1990s
Hook depth (m)Hook depth (m)
00 10100000 20020000 30030000
1950s1950s
1990s1990s
Hooks per Hooks per operationoperation
SummarySummary
Similar Similar • geargear• seasonseason• time of time of
dayday
Different Different • areaarea• depth rangedepth range• soak timesoak time• number of number of
hookshooks
)log()log( ,,5,4,3,2,10, sisisisisisisi hDTENP
Generalized linear model:Generalized linear model:
mass index = mean weight x mass index = mean weight x cpuecpue
Black marlinBlack marlin
AlbacoreAlbacore
SwordfishSwordfish
YellowfinYellowfinBigeyeBigeye
Silky sharkSilky sharkBlue sharkBlue shark
Oceanic whitetipOceanic whitetipBlue marlinBlue marlin
Mako sharksMako sharksStriped marlinStriped marlin
Thresher sharksThresher sharks
SailfishSailfish
SkipjackSkipjackLancetfishesLancetfishes
WahooWahoo
Mahi mahiMahi mahi
BarracudasBarracudasSSpearfishpearfish
Pelagic rayPelagic rayCrocodile sharkCrocodile shark
PomfretsPomfrets
0.01 0.1 1 10 100
Large Large predatorpredatorss
Small Small speciesspecies
Rare Rare speciesspecies
Change in mass or cpueChange in mass or cpue
increaseincreasedecreasedecrease
00 2020 4040 6060 8080 100100
00200
200
400
400
Yellowfin tuna sizeYellowfin tuna size
1950s1950s
00 2020 4040 6060 8080 100100
00500
500
150
0150
0250
0250
0
1990s1990s
Size (Size (kgkg))
Size (Size (kgkg))
1950s 1950s mean sizemean size ((kgkg))
1990
s m
ean
size
1990
s m
ean
size
((kgkg))
00 4040 8080 120120
002
02
04
04
06
06
0
BlBlueue marlin marlinMako sharksMako sharks
MahiMahi mahi mahi
Change in body sizeChange in body size
Change in index with sizeChange in index with size
1950s 1950s mean size mean size ((kgkg))
Ch
an
ge i
n i
nd
ex
of
mass
Ch
an
ge i
n i
nd
ex
of
mass
00 4040 8080 120120
0.010.01
0.10.1
11
1010
BlBlueue marlin marlin
Mako sharksMako sharks
MahiMahimahimahi
• Reductions in size and Reductions in size and cpue of large predatorscpue of large predators
• Modest change in small Modest change in small speciesspecies
• Appearance of several Appearance of several new speciesnew species
• Reduction in index of Reduction in index of massmass
ConclusionsConclusions
50 0 50
020
4060
8010
012
0
100 50 0 50 100
Mean size (kg)Mean size (kg)
Cpu
e (n
o./1
000
hook
s)C
pue
(no.
/100
0 ho
oks)
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