SCRS/2009/106

SCRS/2009/106
Collect. Vol. Sci. Pap. ICCAT, 65(4): 1401-1407 (2010)
CONVERSION ON SAMPLED-CAS INTO CAA OF THE NORTH ATLANTIC
TAIWANESE ALBACORE CATCH, DATING FROM 1981 TO 2008,
USING KNIFE CUTTING ALGORITHM
Feng-Chen Chang1, Yin Chang2 and Shean-Ya Yeh3
SUMMARY
Catch at age (CAA) data has always been very important, even indispensable, piece of
information required for modern fisheries stock assessment modeling exercises. Although quite
a few models already to include conversion algorithms of catch at size (CAS) into CAA, to set
aside such conversion as separate procedure will be much beneficial mainly due to the
complexity of type of fisheries with specification of circumstances. As one of the major fishing
fleets targeting on North Atlantic albacore resource, Taiwan Fisheries Agency has long been
endeavouring on collecting North Atlantic albacore’s catch at size data from its operating
vessels. Monthly random sampled CAS, which was summed up from those reported Taiwanese
North Atlantic operating longliners, of Taiwanese albacore catch by area 31 and area 32 were
firstly compiled. A conversion on CAS into CAA was then applied at this point by using knife
cutting algorithm accompanied with its derived mean weight per fish, based on obtained age
distribution and official age-weight growth equation. Yearly Taiwanese CAA, based on
reported sampled vessels, by areas 31 and 32 were then summed up with its corresponding total
estimated weight were also provided. The area-time table of Taiwanese CAA provided in this
document has to be raised to match with its Task 1 catch reports. The standard procedure of
size measuring only the first 30 fishes of catch is a very good random sampling setup, it is
noticed that the level (monthly/seasonally/yearly) of compilation procedure, however, may
result in different figures.
RÉSUMÉ
Les données de prise par âge (CAA) ont toujours constitué un élément d’information très
important, voire indispensable, pour les exercices de modélisation réalisés dans les évaluations
de stocks des pêcheries modernes. Même si quelques modèles incluent déjà des algorithmes de
conversion de la prise par taille (CAS) en prise par âge (CAA), le fait de mettre de côté cette
conversion comme procédure distincte sera très bénéfique, surtout en raison de la complexité
du type de pêcheries avec spécification des circonstances. Etant l'une des principales flottilles
de pêche ciblant le germon dans l’Atlantique Nord, l’Agence des pêches du Taïpei chinois
s’efforce depuis longtemps de recueillir les données de prise par taille du germon de
l’Atlantique Nord auprès de ses navires opérationnels. Tout d’abord, on a obtenu la CAS
mensuelle en additionnant les échantillonnages aléatoires de la capture de germon du Taïpei
chinois de la zone 31 et la zone 32 déclarée par les palangriers du Taïpei chinois opérationnels
dans l’Atlantique Nord. Une conversion de la CAS en CAA a ensuite été appliquée à ce stade en
utilisant un algorithme de découpage en arête vive accompagné de son poids par poisson dérivé,
sur la base de la distribution de l’âge obtenue et de l’équation officielle de croissance
âge-poids. La CAA annuelle du Taïpei chinois, basée sur les navires échantillonnés et déclarés,
dans les zones 31 et 32, a ensuite été ajoutée à son poids total estimé correspondant, et elle a
été communiquée. Le tableau spatiotemporelle de la CAA du Taïpei chinois fourni dans le
présent document doit être extrapolé afin qu’il corresponde à ses rapports de capture de la
Tâche I. La procédure standard consistant à mesurer la taille des 30 premiers poissons de la
capture est un système d’échantillonnage aléatoire très satisfaisant ; il convient de noter que le
niveau (mensuel/saisonnier/annuel) de la procédure de compilation peut toutefois produire des
chiffres différents.
1
2
3
Institute of Oceanography, National Taiwan University, Tainan 701, Taiwan; E-mail: [email protected]
Overseas Fisheries Development Council, Taipei 106, Taiwan; E-mail: [email protected] ; [email protected]
National Cheng kung University, Tainan 701, Taiwan; E-mail: [email protected]
1401
RESUMEN
Los datos de captura por edad (CAA) han sido siempre una parte muy importante de la
información, incluso indispensable, para los ejercicios de modelación de las evaluaciones de
stocks de las pesquerías modernas. Aunque pocos modelos incluyen ya algoritmos de
conversión de captura por talla (CAS) en captura por edad (CAA), dejar aparte dicha
conversión como procedimiento separado sería muy beneficioso debido principalmente a la
complejidad del tipo de pesquerías con especificación de las circunstancias. Como una de las
principales flotas pesqueras que se dirige al atún blanco del Atlántico norte, la Agencia de
Pesca de Taipei Chino lleva tiempo esforzándose en recopilar datos de captura por talla del
atún blanco del Atlántico norte de sus buques operativos. En primer lugar, se obtuvo la CAS
mensual sumando los muestreos aleatorios de la captura de atún blanco de Taipei Chino de la
zona 31 y la zona 32 comunicada por los palangreros de Taipei Chino operativos en el
Atlántico norte. Se aplicó entonces una conversión de CAS a CAA utilizando un algoritmo de
filo de cuchillo acompañado de su peso medio por pez derivado, basándose en la distribución
por edad obtenida y en la ecuación oficial de crecimiento edad-peso. La CAA anual de Taipei
Chino, basada en los buques muestreados en las zonas 31 y 32, se sumó a su peso
correspondiente total estimado y también se facilitó. La tabla área-tiempo de la CAA de Taipei
Chino que se facilita en este documento debe extrapolarse para que se corresponda con sus
informes de captura de Tarea I. El procedimiento estándar de medir la talla de los primeros 30
peces de la captura es un buen procedimiento de muestreo aleatorio, y cabe señalar que el
nivel del procedimiento de recopilación (mensual/estacional/anual), sin embargo, puede
producir cifras diferentes.
KEYWORDS
Size distribution, age composition, Atlantic albacore, long lining
1. Introduction
In the Atlantic Ocean, two stocks of albacore (Thunnus alalunga), separated by 5° N latitude, were assumed for
the fishery management. Taiwan is one of the main fishing nations utilizing the North Atlantic albacore resource,
and contributes a significant part to the total landings. As one of the main fishing nations, it is equally our
responsibility to acquire the catch and size statistics for the purpose of monitoring its status.
Fisheries biologists have utilized the information from commercial catches in their research for a long time.
Usually, the information of commercial catches is presented as size-frequency distributions. We need to convert
the Catch-at-size (CAS) data to Catch-at-age (CAA) data if any age-structured stock assessment model is
intending to be applied. For estimating age composition from its corresponding size distribution, such as CAS
obtained from the reported North Atlantic albacore size measurement from Taiwanese longline fishing vessels,
several usable methods are available (Fournier et al., 1998). Traditional Knife Cutting Algorithm, assumed that
fish growth pattern is a step-function style and never over-growth across the mid-point of the nearby age
boundary, which was assigned by an official age-growth relation formula. The beauty part of this algorithm is
that one size distribution will only get a firmed age distribution under a known age-size growth relationship.
In this study, Knife Cutting Algorithm was used to convert observed catch at size distribution into its
corresponding catch at age composition by fish number. The mean weight of a catch at age composition will be
also evaluated according to official age-weight growth equation. Since size observation is obtained by summed
up those reported Taiwanese longline vessels of its daily first 30 fishes of catch, the area-timely CAA tables
provided in this document must be further raised according to the summed total North Atlantic albacore catch
derived in this study versus its corresponding Task I catch reports.
2. Materials and methods
Taiwanese longline catch and size data, compiled by year and by ICCAT sampling area, from 1981 to 2008 were
the major source of data used in this analysis. These data were kindly provided by the Overseas Fisheries
Development Council (OFDC), which is an organization mainly supported by Taiwan Fisheries Agency.
1402
As one of the major fishing fleets targeting on North Atlantic albacore resource, Taiwan Fisheries Agency has
long been endeavouring on collecting North Atlantic albacore’s catch at size data from its operating vessels.
Monthly random sampled CAS, which was summed up from those reported Taiwanese North Atlantic operating
longliners, of Taiwanese albacore catch by area 31 and area 32 were firstly compiled. A conversion on CAS into
CAA was then applied at this point by using knife cutting algorithm accompanied with its derived mean weight
per fish, based on obtained age distribution and official age-weight growth relationship. Yearly Taiwanese CAA
(based on reported sampled vessels) by areas 31 and 32 were then summed up with its corresponding total
estimated weight were also provided.
3. Results and discussion
Results of converted CAA of Taiwanese reported CAS of area 31 and area 32 with its corresponding mean
weight were shown in Table 1 and Table 2, accordingly. The total combined yearly Taiwanese CAA of North
Atlantic albacore sampled with its corresponding Task 1 reported removal were shown in Table 3.
In general, albacore caught in area 32 is bigger than caught from area 31. The majority of Taiwanese catch of
albacore is greater than age 3 in area 31 and is greater than age 4 in area 32. It has been very unfortunate that the
reported size information in area 31 in 1990s was very rare, as shown in Table 1. As indicated in Table 3, the
raising factor has to be considered because the sampled CAA total weight was always smaller than the reported
Task 1 removal.
Results of monthly albacore mean weight, obtained from weighing each age of weight (which follows official
age-weight growth equation) by converted CAA percentage composition, by area was shown in Figure 1.
Although data of 1990s in area 31 were scarce, it is interestingly to note that the monthly mean weight in late
2000s seemed heavier than those in 1980s. Whether it is somehow related to oceanic condition change is a very
interesting point for further investigation.
Acknowledgments
We are most grateful to the Taiwan Fisheries Agency for giving incentives as well as financial supports to
pursuit this analysis.
References
Hsieh, C.H., Chang, F.C. and Yeh, S.Y. 2008, Standardized northern Atlantic Albacore (Thunnus alalunga)
CPUE, from 1967 to 2005, based on Taiwanese longline catch and effort statistics. Collect. Vol. Sci. Pap.
ICCAT, 62(3): 847-857.
Fournier, D.A., Hampton, J., and Sibert, J.R. 1998, Multifan-CL: A length-based, age-structured model for
fisheries stock assessment, with application to South Pacific albacore, Thunnus alalunga. Can. J. Fish.
Aquat. Sci. 55: 2105-2116.
Chang, Y. and Yeh, S.Y. 2004, Comparison between optimal searching algorithm versus knife-edge cutting age
composition. Collect. Vol. Sci. Pap. ICCAT, 56(4): 1417-1427.
1403
Table 1. Samples of aged fishes in ICCAT sampling area 31 from 1981 to 2008.
Year Area
1
1981 31 55
1982 31 93
1983 31 192
1984 31 319
1985 31 95
1986 31 44
1987 31 6
1988 31 1989 31 1990 31 1991 31 1992 31 1993 31 1
1994 31 1995 31 1996 31 1997 31 1998 31 1999 31 2000 31 2001 31 2002 31 2003 31 2004 31 2005 31 2006 31 2007 31 2008 31 - : no data
Age
2
3
4
5
6
7
8
9
989 3044 5925 7814 4649 1561 549 185
1687 9192 13178 11734 7085 3130 1985 1137
524 3559 11829 17354 7508 1768 1065 709
438 8282 16175 18183 12504 5618 2892 1513
253 1083 9583 11988 9950 4319 2089 1250
1228 2519 4979 10711 6680 3220 2756 1452
953 3811 3664 4593 2070 729 432 81
- 1136 268
5
- 1186 311
3
1 805
93
1
1 167 935 332 514 330 130 40
80
50
95
37
1
- 128 440
- 112 734 929 344 60 14
- 14 849 2763 4326 5064 2705 485
- 21 1371 2695 3155 2305 719 95
- 287 1656 4288 3548 1552 779 213
12 204 2443 1863 1910 1384 586 211
- 42 965 1410 1586 1963 1619 561
17 189 491 2035 2088 1184
1404
Total
10+ samples
218 24989
2046 51267
1896 46404
2405 68329
2674 43284
1784 35373
210 16549
1409
1500
900
16
2466
130
133
568
3
2196
109 16315
16 10377
185 12508
111
8724
926
9072
1059
7063
Mean Wt. Total samples
(kg)
* Mean Wt.
17.6508
441076
17.0107
872088
20.9578
972527
16.4392
1123273
20.4692
885990
18.6460
659564
14.6230
241996
15.9043
22409
16.0837
24125
16.1610
14545
19.1131
47133
14.0113
1821
13.3240
1772
15.5632
8840
18.4961
40617
22.5544
367975
20.7289
215103
20.8136
260336
20.8885
182231
26.2006
237692
29.1190
205668
Table 2. Samples of aged fishes in ICCAT sampling area 32 from 1981 to 2008.
Year Area
Age
2
3
4
5
6
7
8
9
10+
1
32 31
2
39 2479 3943 3330 6044 5065 3409 6744
1981
32 37 161 1552 2104 6261 10633 8338 6713 4344 10528
1982
32 258
12 594 4459 16476 15940 15499 6560 5477 5397
1983
32 516 1164 5390 6729 14600 23046 20292 11804 5486 13515
1984
32 104 182 3297 5099 12585 19566 14023 8312 3776 11666
1985
32 28
46 204 5545 7889 12896 11603 6295 3200 10639
1986
32
1 189 1679 2370 1445 1412 1587 2270 1230 3012
1987
32
1988
32 28
19
720 2197
342
11
1989
32
2
867 2373
255
17
9
167
1990
32
90 1738 2223
151
10
15
53
1991
32
5
21
41
59
110
303
1992
32
2
38 228 1149 1127
787
301
322 145
142
1993
32
2
11
23
92
70
61
51
22
23
147
1994
32 18
53 161 681
638
426
199
101
18
15
1995
32
1 108 138 196
553
924
468
307 132
75
1996
32
- 112
874 1266 1146 1104 716
549
1997
32
1
5 1238 3534 1851 572
10
1998
32
- 135
4 1340 4711 1982 308
11
1999
32
5
544 4085 1125
45
12
2000
32
11 463
357
3
1
2
2001
32
1
2 510
780 1762 2106
657 161
117
2002
32
12 106 1807 5242 5651 8144 3421 898
386
2003
32
23 1001 3038 4749 10861 6287 4637 1964 2631
2004
32
50 1617 4143 9283 9799 4551 1550
579
2005
32
- 512 4207 6083 10061 9604 5741 2415 1390
2006
32
2
61
409 3673 5904 4977 2037
445
2007
32
6
29 576
771
452 1124 1192 654 1257
2008
- : no data
1405
Mean Wt. Total samples
Total
samples
(kg)
* Mean Wt.
31086
24.9381
775227
50671
21.6445
1096750
70672
21.6392
1529289
102542
22.6581
2323407
78610
23.2591
1828400
58345
23.2573
1356948
15195
21.0585
319984
3317
16.2465
53890
3690
27.4772
101391
4280
21.3610
91425
539
28.7743
15509
4241
22.9674
97405
502
23.0809
11587
2310
18.7655
43348
2902
19.0496
55282
5767
21.9676
126687
7211
26.1212
188360
8491
25.2021
213991
5816
25.3826
147625
837
15.1958
12719
6096
22.1891
135265
25667
21.6981
556925
35191
22.0261
775121
31572
23.5155
742432
40013
22.0596
882669
17508
26.2921
460322
6061
25.2738
153184
Table 3. Samples of aged fishes in the northern Atlantic Ocean from 1981 to 2008.
Year
1
2
1981 86 991
1982 130 1848
1983 450 536
1984 835 1602
1985 199 435
1986 72 1274
1987 7 1142
1988 1989 28 19
1990 1991 1992 1993 3 39
1994 2 11
1995 18 53
1996 1 108
1997 1998 1999 2000 2001 2002 1
2003 - 12
2004 - 23
2005 2006 - 12
2007 2008 6
- : no data
3
3083
10744
4153
13672
4380
2723
5490
395
23
161
138
11
2
120
1022
337
716
44
29
Age
4
5
6
7
8
8404 11757 7979 7605 5614
15282 17995 17718 11468 8698
16288 33830 23448 17267 7625
22904 32783 35550 25910 14696
14682 24573 29516 18342 10401
10524 18600 19576 14823 9051
6034 6038 3482 2316 2702
1136 988 2202 342
11
1188 1178 2376 255
17
91 2543 2316 152
10
5
21
41
59
2084 1459 1301 631 452
61
51
22
92
70
681 638 426 199 101
196 553 924 468 307
112 874 1266 1146 1104
1
5 1238 3534 1851
215
54 1340 4711 1982
95
42 544 4086 1125
591 797
3
622 1514 2691 2450 717
2656 8005 9977 13208 6126
4409 7444 14016 8592 5356
3273 8431 12831 11351 5330
6650 7946 11971 10988 6327
1026 1819 5259 7867 6596
593 960 943 3159 3280
1406
9
3594
5481
6186
6999
5026
4652
1311
9
15
110
185
23
18
132
716
572
308
45
1
175
1383
2059
1763
2626
2598
1838
10+
6962
12574
7293
15920
14340
12423
3222
167
53
303
158
147
15
75
549
10
11
12
2
120
495
2647
764
1501
1371
2316
Total Total Wt.
samples
(mt)
56075
1216
101938
1969
117076
2502
170871
3447
121894
2714
93718
2017
31744
562
4726
76
5190
126
5180
106
539
16
6707
145
502
12
2310
43
2902
55
5767
127
7211
188
8621
216
5949
149
1405
22
8292
176
41982
925
45568
990
44080
1003
48737
1065
26580
698
13124
359
Task 1
(mt)
6584
10500
14254
14923
14899
19646
6636
2117
1294
1651
4318
2209
6300
6409
3977
3905
3330
3098
5785
5299
4399
4330
4557
4278
2540
2357
1297
1107
Mean Wt. of North Atlantic albacore from 1981 to 2008.
45
40
35
Mean Wt. (kg)
30
25
Area 31
Area 32
20
15
10
5
0
198101
198401
198701
199001
199301
199601
199901
200201
200501
200801
Year/Month
Figure 1. Mean weight of North Atlantic albacore (kg) based on the Taiwanese longline fishery data set from
1981 to 2008.
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