Download - Peter Ward RAM Myers Dalhousie University
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Peter WardPeter WardRAM MyersRAM Myers
Dalhousie UniversityDalhousie University
The effects of soak time andThe effects of soak time anddepth on longlinedepth on longline
catch ratescatch rates
EB WP-3 EB WP-3
EB WP-12EB WP-12
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200 m
400 m
500 m
1950s1950s 1990s 1990s
DepthDepth 25–175 m25–175 m 25–500 m 25–500 mDawnDawn 35%35% 30%30%DuskDusk 0% 0% 70% 70% Soak timeSoak time 5 hr 5 hr 9 hr 9 hr
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Observer data from six fisheriesObserver data from six fisheries
00
20S20S
40S40S
20N20N
40N40N
140E140E 180E180E 140W140W
Western PacificWestern Pacific Bigeye Bigeye (1,915 sets) (1,915 sets)
Central PacificCentral PacificBigeye (3,243 sets)Bigeye (3,243 sets)
Western Pacific Western Pacific Distant (234 sets)Distant (234 sets)
North Pacific Swordfish (1,539 sets)North Pacific Swordfish (1,539 sets)
South PacificSouth PacificYellowfin (1,419 sets)Yellowfin (1,419 sets)
South Pacific SBT (666 sets)South Pacific SBT (666 sets)
>500,000 fish>500,000 fish>6,000 daily sets>6,000 daily sets
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Swordfish2.52.5
2.02.0
1.51.5
1.01.0
0.50.5
00
Cat
ch r
ate
(no.
/100
0 ho
oks)
Soak time (hr)00 55 1010 1515 2020
DataData
++Estimate of Estimate of deployment time deployment time from start and end from start and end of time of setof time of set
Observer record of Observer record of time when each time when each hook was retrievedhook was retrieved
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(1) Random effects (O)(1) Random effects (O)
• soak time (soak time (TT))
• season (season (SS))
• year (year (Y)Y)
• dawn (dawn (AA))
• dusk (dusk (PP))
OPAYST 543210 PAYST 543210 AYST 43210 YST 3210 ST 210 T10
Generalized linear mixed modelGeneralized linear mixed model
(2) Fixed effects(2) Fixed effects
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Soak time effect-0.2 0.0 +0.2
bigeyebigeye
skipjackskipjack
swordfishBillfishes
Tunas
blue sharkblue shark
Sharks and rays
albatrossalbatross
Other fishes
Soak time effect varies among speciesSoak time effect varies among speciesSeabirds
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Soak time effect correlated with survivalSoak time effect correlated with survival
00 2020 4040 6060 8080 100100
Alive (%)Alive (%)
Soa
k ti
me
effe
ctS
oak
tim
e ef
fect
0.0
0.0
-0.1
-0.1
+0.
1+
0.1
r = 0.54r = 0.54
blue sharkblue shark
skipjack tunaskipjack tuna
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-1.0-1.0 -0.5-0.5 0.00.0 0.50.5 1.01.0
-1.0
-1.0
-0.5
-0.5
0.0
0.0
0.5
0.5
1.0
1.0
Dus
k ef
fect
Dus
k ef
fect
Dawn effectDawn effect
oilfishoilfish
Dusk has a positive Dusk has a positive effect for many effect for many speciesspecies
blackblackmarlinmarlin
Ray’s breamRay’s bream
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Effects make a substantial differenceEffects make a substantial difference
$1,500 vs $5,000$1,500 vs $5,000
SwordfishSwordfish 5 hr5 hr 20 hr20 hr
no dawn or duskno dawn or dusk 1 4dawn and duskdawn and dusk 3 10
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00 11 22
Bigeye tunaBigeye tunaDayDay
500500
400400
300300
200200
100100
Dep
th (
m)
Dep
th (
m)
Relative catchabilityRelative catchability
00
NightNight
Striped marlinStriped marlinBlue sharkBlue sharkOpahOpah Distribution of Distribution of catches of most catches of most species varies with species varies with depthdepth. . . and with time . . . and with time
of dayof day
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ConclusionsConclusions(1) Abundance indices need to be adjusted for:(1) Abundance indices need to be adjusted for:
• soak timesoak time
• dawn and duskdawn and dusk
• depth rangedepth range
(2) Mortality of several species may be greater (2) Mortality of several species may be greater than indicated by catch recordsthan indicated by catch records
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Logistic regressionLogistic regression
ππ is the probability of catching a fish:is the probability of catching a fish:
hp
p=÷
ø
öçè
æ-1
log
( )h
hp
e
e+
=1
Generalized linear mixed modelGeneralized linear mixed model
catch catch y y has a binomial distribution:has a binomial distribution: y~b(n,y~b(n,ππ))
ηη is the ‘soak time effect’: is the ‘soak time effect’:
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RandomRandom effects effects
• Operations drawn from a larger Operations drawn from a larger population of operationspopulation of operations
• Random effects in catch rate – soak Random effects in catch rate – soak time relationship for each operationtime relationship for each operationare independent and normally are independent and normally distributed: distributed:
),0(~ 2 Ni
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Catch is the product of capture and loss Catch is the product of capture and loss ratesrates
2020151510105500
Soak time (hr)
Pro
babi
lity
of
bein
g on
a h
ook
No captures afterNo captures afterdeployment e.g. seabirdsdeployment e.g. seabirds
ββ < 0 < 0
Captures exceed lossesCaptures exceed lossese.g. blue sharke.g. blue shark ββ > 0> 0
ββ = 0= 0
ββ < 0< 0Losses eventually Losses eventually exceed capturesexceed capturese.g. skipjacke.g. skipjackCaptures balance lossesCaptures balance lossese.g. yellowfine.g. yellowfin
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Sth slope
NE
slo
pe
0.0 0.05 0.10 0.15 0.20
-0.0
4-0
.02
0.0
0.02
0.04
0.06
0.08
0.10
porbeagle
swordfishoilfish
escolar
blue shark
Soak time effect generally consistent Soak time effect generally consistent among areasamong areas
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Mesopelagic communityMesopelagic community
swordfishswordfish opahopahbigeye tunabigeye tuna
500m500m
400m400m
300m300m
200m200m
100m100m
0m0m
Epipelagic communityEpipelagic community
striped marlinstriped marlin
yellowfin tunayellowfin tuna
wahoowahoo