SHOU
PICES 17th Annual Meeting
The biology of skipjack tuna (The biology of skipjack tuna (KatsuwonusKatsuwonus pelamispelamis) )
((PerciformesPerciformes: : ScombridaeScombridae) caught by purse ) caught by purse seinerseiner
in the Western and Central Pacific Ocean: in the Western and Central Pacific Ocean:
Comparative analysis between Comparative analysis between Floating object Floating object associated school and unassociated schoolassociated school and unassociated school
Guoping ZHULiuxiong XU, Xuefang WANG, Xuchang YE, Chunlei WANG
College of Marine Sciences
Shanghai Ocean University
999 Hucheng Ring Road, Lingang New Town,
Shanghai 201306
P.R. China
PICES 17th Annual Meeting2
Outline
Summary
Discussions
Results
Materials and Methods
Introduction
Source: http://www.kuuloakai.com/images/aku_large.gif
Short-lived speciesGrowth rapidlyRapid population turnoverHigh resilience to fishing
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Introduction
Number of purse seine vessels operating in the WCPO in 1972 -2007
Skipjack in the WCPFC purse seine fishery –Catch, delivered value of
catch and composite price
Source: Williams and Terawasi (2008)
Purse seine fishery
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Introduction
A fish aggregating device (FAD) deployed in the Bismark Sea, Papua New Guinea
Source: www.collapse.com.au/source/pacific12.html
Floating object associated school
Unassociated school
UNA school
FOB school
Source: http://tunaseiners.com/
Be classified by set type categories
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Introduction
The Fisheries Ministers of the Federated States of Micronesia, Kiribati, Marshall Islands, Nauru,
Palau, Papua New Guinea, Solomon Islands and Tuvalu,
further banned the use of Fishing Aggregating Devices [FADs], a device used to draw juvenile
bigeye and yellowfin tuna in the PNA Members’ EEZs in the third
quarter of each year.
Source: www.fis.com
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Introduction
Many literatures are report the biology of skipjack (such as Batts 1972a, Batts1972b, Wild and Foreman 1980, Chur and Zharov 1983, Richardson and Georgeha1987, Sosa-Nishizaki et al. 1989, Nootmorn and Panjarat 2001, Andrade and Campos 2002). However, few studies are focus on comparing the biology of skipjack between the FOB school and the UNA school.
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Introduction
The aim of the present study:
To compare the biological traits of skipjack inhabiting the WCPO waters between the FOB school and the UNA school from the fork length distribution, the length-weight relationship, sex ratio, size at sexual maturity and stomach fullness stage
To further provide the information to fishery management.
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Materials and Methods
Study area and data sampling
Equator
975—— the UNA school
1346 —— the FOB school
UNA schoolFOB school
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Materials and Methods
Fork length (FL) distribution
The difference of FL distribution between sexes was tested by two-sample Kolmogorov-Smirnov test (K-S test). The 95% confidence intervals of mean FL were estimated from running 1000 bootstrap runs.
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Materials and Methods
Length-Weight relationship
ebW aL ε= ε~ N (0, σ2)
The parameters (a and b), the coefficient of determination (r2) and the standard errors (S.E.) were estimated over the entire period by least squares regression using the log transformed weights and sizes.
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Materials and Methods
Regression analysis was done separately for males and females. The analysis of t-test was used to examine the difference of slope between sexes in the two fish schools. If no significant difference between sexes can be found, the difference of slope between the two fish schools is then tested by t-test after combined the samples.
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Materials and Methods
The differences of length-weight relationship between sexes were tested by ANCOVA (ANalysis of COVAriance). If no significant difference between sexes can be found, the difference of length-weight relationship between the two fish schools is then tested by ANCOVA after pooled the samples. The hypothesis of isometric growth was tested using the t-test (P < 0.05).
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Materials and Methods
Sex ratio
Sex ratio was calculated as the proportion of males by size class (5cm). For each fork length class, Chi-square (χ2) tests were used to test for any significant difference to the theoretical ratio of 1:1.
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Materials and Methods
Size at 50% sexual maturity (L50)
For each ovary, the oocytes in the most-developed mode were classified as:
Ⅰ- Undeveloped stage;
Ⅱ - Early developing stage;
Ⅲ - Later developing stage;
Ⅳ - Mature stage;
Ⅴ - Spawned stage;
Ⅵ - Spent stage
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Materials and Methods
The size at which 50% of fish were sexually mature was estimated for reproductively active fish (Stages Ⅳ–Ⅵ) per 5 cm size-class by fitting a model
50( )1L L L
GPe δ− −=
+PL is the proportion of the mature fish at length L,
G is maximum attainable proportion of the mature fish in the analysis;
L50 and δ (the rate at which maturity is attained) are the parameters to be estimated.
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Materials and Methods
The above parameters (L50 and δ ) were estimated by non-linear minimization of a negative binomial log-likelihood
ln ln ln(1 )1
LL L L
L L
PL y n PP
⎛ ⎞− = + −⎜ ⎟−⎝ ⎠
∑yL is the observed numbers of fish mature in a total nL of fish sampled in length
class L.
Maximum-likelihood estimates of the parameters were obtained using the routine
SOLVER in the Microsoft Excel and calculating the likelihood of immature and
mature individuals as 1- PL and PL .
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Materials and Methods
Stomach fullness
The analysis of two-factor contingency table was used to analyze the difference of skipjack tuna’s stomach fullness between the UNA school and the FOB school (p<0.05).
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02468
10121416
226-250
276-300
326-350
376-400
326-450
476-500
526-550
576-600
626-650
676-700
726-750
Fork length classes (cm)
Perc
enta
ge o
f ind
ivid
ual (
%)
Results
Fork length distribution
FOB school
UNA school
K-S test; Z=0.32, P<0.05
243 – 733 mm
421 mm
243 – 746 mm
515 mm
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Results
t-test ANCOVA
t p F p
Female -12.0811 0.1744 3.1989 0.0290 357
Male -11.9561 0.2543 3.1758 0.0421 295
Combined -12.3050 0.0910 3.2362 0.0151 975
Combined -11.6277 0.1248 3.1386 0.0200 1345
Female -12.1675 0.2214 3.2275 0.0357 458
Male -11.3087 0.2636 3.0885 0.0424 436
52.9360 <0.001 0.5641 >0.05
133.8678 <0.001 244.5427 <0.001
FOB school
7.9833 <0.001 0.3585 >0.05
UNA school
School type Sex Intercept S.E. Slope S.E. Number
The body weight – fork length relationship of skipjack tuna by sex and school type.
Weight –length relationship
BW=0.000005666FL3.1989
n=357
BW=0.000005197FL3.2276
n=458
BW=0.000006550FL3.1758
n=295
BW=0.000004529FL3.2362
n=975
BW=0.000001227FL3.0885
n=436
BW=0.000008915FL3.1386
n=1345
FOB school - Female
0
2000
4000
6000
8000
10000B
ody
wei
ght (
g)
FOB school - Male
0
1000
2000
3000
4000
5000
6000
7000
Bod
y w
eigh
t (g)
UNA school - Female
UNA school - Male
UNA school - Combined
0 200 400 600 800
Fork length (mm)
FOB school - Combined
0
2000
4000
6000
8000
10000
12000
0 200 400 600 800
Fork length (mm)
Bod
y w
eigh
t (g)
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Results
UNA school: 501 - 550mm (χ2=4.00, P<0.05) and 601 - 650mm (χ 2=4.17, P<0.05)
FOB school: 301 - 350mm (χ 2=7.78, P<0.05) and 351 - 400mm (χ 2=4.00, P<0.001)
Sex ratio
0.0
0.2
0.4
0.6
0.8
1.0
200-250
251-300
300-350
351-400
451-450
451-500
501-550
551-600
601-650
651-700
701-750
Fork length classes (cm)
Sex
ratio
UNA schoolFOB school
0.45 for the UNA school
0.49 for the FOB school
y = 0.0178x + 0.3764 R2=0.2585y = 0.0514x + 0.1587 R2=0.7421
Sex ratio of skipjack tuna with pooled data by school type (in 50 mm interval)
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0.0
0.2
0.4
0.6
0.8
1.0
0 200 400 600 800Median of Fork length classes (cm)
Perc
enta
ge o
f ind
ivid
ual
0.0
0.2
0.4
0.6
0.8
1.0
0 200 400 600 800Median of Fork length classes (cm)
Perc
enta
ge o
f ind
ivid
ual
Results
(Female)
FOB school - Observed
FOB school - Predicted
UNA school - Observed
UNA school - Predicted
498.64 mm427.55 mm
488.51 mm448.99 mm
Size at 50% sexual maturity
(Male)
FOB school - Observed
FOB school - Predicted
UNA school - Observed
UNA school - Predicted
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Results
0102030405060708090
100
250-300
300-350
351-400
451-450
451-500
501-550
551-600
601-650
651-700
701-750
Fork length classes (cm)
Perc
enta
ge o
f sto
mac
h fu
llnes
s
Ⅳ
Ⅲ
Ⅱ
Ⅰ
Empty stomach
250-300
300-350
351-400
451-450
451-500
501-550
551-600
601-650
651-700
701-750
Fork length classes (cm)
0102030405060708090
100
250-300
300-350
351-400
451-450
451-500
501-550
551-600
601-650
651-700
701-750
Fork length classes (cm)
Perc
enta
ge o
f sto
mac
h fu
llnes
s
Ⅳ
Ⅲ
Ⅱ
Ⅰ
Empty stomach
250-300
300-350
351-400
451-450
451-500
501-550
551-600
601-650
651-700
701-750
Fork length classes (cm)
The analysis of two-factor contingency table indicate that significant difference occur for both the UNA school (χ 2=134.69, P=<0.001) and the FOB school (χ 2=91.36, P=<0.001) among each fork length classes .
Diet
UNA schoolFOB school
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The present study - FOB schoolThe present study - UNA school
Discussions
W-L relationship
0
5000
10000
15000
20000
25000
200 243 280 330 370 420 470 520 570 620 670 719 740 780 830 880
Fork length (cm)
Tota
l wei
ght (
g)
Tester and Nakamura (1957)
Chatwin (1959)
Vooren (1976)
Yang et al. (2005)
Wang et al. (2008) - unassociated school
Wang et al. (2008) - associated school
Comparison of the body weight – fork length relationship for skipjack tuna estimated in the present study (heavy line) with the body weight –fork length relationships estimated by other authors
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Discussions
Source Study area Female-male ratio Comments
Brock(1954) Hawaii 1 : 1.16 Baitboat
Habib (1978) New Zealand 1 : 0.76 Purse seine
Marr(1948) North of Marshall Isalands 1 : 1.60 -
Raju(1964) Philippines 1 : > 1.00 Males dominant in older groups
Schaefer and Orange (1956) Eastern Pacific 1 : 0.73 Small fish; sex indeterminate for large proportion
Tester and Namamura (1957) Hawaii 1 : 1.57 Inshore trolling
Yoshida (1960) Southern and Central Pacific 1 : 1.05
Wade (1950) Philippines 1 : 0.86
Waldron (1963) Japan 1 : 1.09
Wang et al. (2008) WCPO 1 : 0.95 UNA school
Wang et al. (2008) WCPO 1 : 0.60 FOB school
The present study WCPO 1 : 0.95 UNA school
The present study WCPO 1 : 0.83 FOB school
1 : 1.00 400 – 490 mm FL
1 : 1.31 500 – 590 mm FL
1 : 1.00 600 – 690 mm FL
Hu and Yang (1972) Taiwan
Comparison on sex ratios of Skipjack tuna from the Pacific Ocean. Partly reproduced from Table 4 of Wild and Hampton (1994)
Sex ratio
Sources Area L50 (mm) Minimum lengths of sexually mature fish (mm)
Comments
Batts (1972) North Carolina Waters 500 454 Female
Batts (1972) North Carolina Waters 435 Male
Matsumoto et al. (1984) 400 - 450 400
Brock (1954) Hawaiian waters 400 - 450
Schaefer and Orange (1956) the eastern Pacific 550
Schaefer and Orange (1956) off Central America ~ 500
Raju (1964a) the Indian Ocean 400 - 450
Simmons (1969) the Atlantic Ocean 410
Stequert (1976) off the northwest coast of Madagascar
410 - 430
The present study WCPO 498.64 342 Female, FOB
The present study WCPO 488.51 433 Male, FOB
The present study WCPO 427.55 413 Female, UNA
The present study WCPO 448.99 434 Male, UNA
Size at first maturity (L50) and minimum length of sexually mature fish for skipjack tuna in the world.
L50
400 ~ 500 mm
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Summary
1) Mean fork length: FOB < UNA.
2) Length-weight relationship: Significant difference can be found between the FOB school and the UNA school.
3) Sex ratio: FOB>UNA. The number of male were lower than female for both fish schools.
4) Size at 50% sexual maturity: FOB >UNA.
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Conclusion, Maybe
“Ban the use of FADs in the PNA
Members’ EEZs in the third quarter of
each year” is a good approach to protect
the skipjack tuna, and other issues also
should be focused on in the future, such
as bycatch of juvenile bigeye and yellowfin
tunas in the purse seine fishery…
SHOU
PICES 17th Annual Meeting
Source: http://www.dfw.state.or.us/mrp/salmon/fishid/Euthynnus_pelamis.jpg
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