historical and recent estimates of the body-size and abundance of pelagic species taken by longline...

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)