SCRS/2009/070
Collect. Vol. Sci. Pap. ICCAT, 65(4): 1268-1281 (2010)
THE AGE AND GROWTH OF ALBACORE TUNA (THUNNUS ALALUNGA)
OF THE NORTH EAST ATLANTIC OCEAN AS INFERRED
FROM THE IRISH PELAGIC TRAWL FISHERY OF 2002
John Boyd
SUMMARY
The age and growth of pelagic trawl caught albacore tuna, Thunnus alalunga was studied by
examining growth rings on cross sections of the first dorsal fin spines. A total of 276 spines from
albacore of between 47cm and 120cm were used from mid water pair trawlers between July and
November of 2002 from the edge of the continental shelf between the Bay of Biscay and the West
Coast of Ireland. A significant linear relationship was found between spine radius and albacore
fork length (r2=0.935). Spine sections were characterised by alternating opaque and translucent
bands and it is proposed that a pair of such bands corresponds to a year’s growth. An age length
key was constructed and three different methods were used to establish von Bertalannfy growth
parameters. These were: excel solver, Ford Walford and bootstrapping using code written in the R
environment. Results from each were similar with a value of around 127cm for L. Values for K
and T0 were around 0.18 and -1.75 years respectively. The average length at age 1 was estimated
to be 50cm. The range of ages estimated was 10 years.
RÉSUMÉ
L’âge et la croissance du germon, Thunnus alalunga, capturé par des chalutiers pélagiques, ont
été étudiés en examinant les anneaux de croissance des sections transversales des épines de la
première nageoire dorsale. Un total de 276 épines de germons, mesurant entre 47 cm et 120 cm, a
été utilisé provenant de chalutiers-bœuf pélagiques entre juillet et novembre 2002 du bord du
plateau continental entre le Golfe de Gascogne et la côte occidentale de l’Irlande. Une relation
linéaire significative a été établie entre le rayon de l’épine et la longueur à la fourche du germon
(r2=0,935). Les sections de l’épine se caractérisaient par des bandes alternativement opaques et
translucides et il a été proposé qu'une paire de ces bandes corresponde à une année de croissance.
Une clé d'identification âge-longueur a été déterminée et trois méthodes différentes ont été
utilisées afin d'établir des paramètres de croissance de von Bertalanfy. Ces paramètres étaient les
suivants : solveur d’Excel, Ford Walford et bootstrap utilisant un code écrit dans l’environnement
de R. Les résultats de chacun d’entre eux étaient semblables à une valeur d’environ 127 cm pour
les valeurs L. pour K et pour T0 étaient d’environ 0,18 et -1,75 ans, respectivement. La taille
moyenne de l’âge 1 estimée était de 50 cm. La fourchette d’âges estimée était de 10 ans.
RESUMEN
Se estudiaron la edad y el crecimiento del atún blanco, Thunnus alalunga, capturado por el
arrastre pelágico examinando los anillos de crecimiento en secciones transversales de las espinas
de la primera aleta dorsal. Se utilizó un total de 276 espinas de atunes blancos de entre 47 cm y
120 cm de arrastreros semipelágicos por parejas, entre julio y noviembre de 2002, del borde de la
plataforma continental entre el Golfo de Vizcaya y la costa occidental de Irlanda. Se descubrió
una relación lineal significativa entre el radio de la espina y la longitud a la horquilla del atún
blanco (r2=0,935). Las secciones de la espina se caracterizaban por bandas opacas y traslúcidas
alternas y se propone que un par de dichas bandas corresponde a un año de crecimiento. Se
construyó una clave de edad talla y se utilizaron tres métodos diferentes para establecer
parámetros de crecimiento de von Bertalanfy. Eran: solucionador de Excel, Ford Walford y
bootstrap utilizando un código escrito en el entorno de R. Los resultados de cada uno de ellos
eran similares con un valor de aproximadamente 127 cm para los valores de L. para K y para T0
eran de aproximadamente 0,18 y -1,75 años, respectivamente. La talla media en la edad 1 se
estimó en 50 cm. El rango de edades estimadas era de 10 años.
KEYWORDS
Pelagic trawl, Thunnus alalunga, albacore, first dorsal spiny ray, age estimation,
bootstrapping, growth marks, North Atlantic, Bay of Biscay
1268
1. Introduction
Albacore tuna are widely distributed in temperate and sub-tropical waters around the globe (Fishbase 2006). In
the Atlantic Ocean three stocks are recognized for the purposes of stock assessment (Anon. 2003). The albacore
studied in this document are a component of the North Atlantic stock, the other two stocks being South Atlantic
and Mediterranean.
Albacore fisheries have been prosecuted from Irish fishing ports since the late 1980s using a variety of gears but
chiefly gill nets and paired mid water trawls. Since 2001 effort has mainly been by paired mid water trawls with
some trolling also taking place. Catch data shows that in 2002 Irish fisheries were supported by a wider range of
stock components than the troll and bait boat fisheries that took most of the North East Atlantic albacore catch in
that year (Ortiz de Zárate et al. 2004). The samples on which the study is based were collected onboard trawlers
by observers primarily in 2002 but with supplementary samples taken in 2003 for ageing purposes. Sample
collection closely followed the development of the fishery in 2002 in the southwest corner of the Bay of Biscay
in July to its conclusion in November off the south west of Ireland.
Fin ray analysis is a well-established age estimation method for marine fish and has been used for a range of
species for at least 80 years (Cass and Beamish 1983). Scales, vertebrae and otoliths have also been used to
determine age of albacore but comparative analysis indicates that spines are the most amenable and reliable
ageing tissue (Fernandez 1992).
Ages assigned from annuli counts have yet to be validated (Ortiz de Zárate et al. 2005). Mark and recapture
experiments using oxytetracycline (OTC) have relied on small numbers of recaptures which to date have shown
a high degree of variability in patterns of annuli formulation (Ortiz de Zárate et al. 1996).
2. Materials and Methods
2.1 Sampling
Albacore were measured to fork length and dorsal fin spines extracted by the method described by CompeánJiménez and Bard (1983). This took place directly after fish were brought aboard with the date and location of
capture also being recorded. A total of 2150 fork lengths and 300 spines were taken. Sampling took place
between July and November of 2002 and followed the development of the fishery onboard a single pair of
pelagic trawlers. The area covered by the samples extended from the Bay of Biscay to the South West coast of
Ireland.
2.2 Spine sectioning and reading
Following the method described by Lee and Yeh (1998) spines were boiled in water for two minutes to remove
connective tissue and skin and then immersed for up to two hours in 3% KOH. The spines were then cut
transversely with a low speed isomet saw into 120mm sections at a point just above the articulating base
(condyle).
2.3 Relationship of spine diameter to fork length
Regression analysis was used to establish the strength of correlation between increasing fork lengths and spine
diameters using the equation:
FL = a + b(R)
Where FL = fork length
a = intercept of the fitted line
b = slope of fitted line
r = radius of the spine section
For the purposes of this analysis spine radius section was defined as the distance between the estimated centre of
the spine and the edge (Compeán Jiménez and Bard 1983).
1269
2.4 Reading sections
Sections were examined under a microscope connected to a flat screen display monitor using transmitted light.
The banding patterns observed consisted of alternating opaque and translucent bands. The pattern most often
observed (in the smaller fish) was a narrow single opaque band followed by a wider translucent band. Taken
together these were interpreted as representing an annual growth cycle consisting of a period of slow growth in
autumn and winter and a faster spring summer growth period. However with increasing size, more complex
patterns were observed: most commonly, two or three clustered narrow opaque bands isolated in wider bands of
translucent material. Following Compeán-Jiminez and Bard (1983) these patterns were identified as alternative
indicators of the annual autumn winter growth phase and therefore as single annuli. Age was estimated by
counting the number of such annuli on each section.
2.5 Vascularisation
Vascularisation of the core was present in all sections though only in larger fish did it become sufficiently
extensive to infer that annuli had been obscured. In such instances bands were inferred by consulting the median
radian value for annuli clearly visible and attributable as products of the first years of life to the age of three.
Similar methods have been used in the past to account for occluded annuli, Cayre and Dioufe (1983), Compeán
Jiminez and Bard (1983), and more recently, Ortiz de Zárate et al. (2005). The number of sections where such
substitutions were made was 20.
With increasing size the progression of opaque and translucent bands became crowded and this increased the
difficulty of distinguishing between opaque and translucent zones and therefore between annuli. This difficulty
was addressed by recounting until an agreed value was agreed.
2.6 Von Bertalannfy parameters
The Von Bertalannfy equation describing the growth of fish is stated as:
Lt=Linf(1-exp[-K(t-t0)])
where
Lt= length at age t
Linf = asymptotic or theoretical maximum length attainable
K = growth rate at which the theoretical maximum siz
e is attained
A number of methods were used to establish the parameters of the equation and produce growth curves:
–
From King 1995, a Ford Wolford plot from which the parameters are obtained from the linear equation:
(Lt)=m (LT+1) + c
where m= slope of the straight line
c= intercept on the y axis
Growth rate was estimated as: K= –ln(m)
Asymptotic length was estimated as Linf =c/(1-m)
–
Solver optimization function in Microsoft excels which identifies Von Bertalannfy parameters for a
minimum sum of squares value.
–
Bootstrapping using code written in the R environment (R-Development-Core-Team 2005). Individual
age-length observations were re-sampled 1000 times and a growth curve was fitted for each bootstrap
sample. The 95% confidence limits were obtained from the 2.5% and 97.5% quantiles of the
bootstrapped growth curves.
3. Results
The age length key obtained from reading 276 dorsal fine spines is shown in Table 1. The bootstrapped ages at
length estimated by three methods are shown in Table 2 with comparative estimates in Table 3. Von Bertalanffy
parameters for the three methods used are shown in Table 4 while Table 5 shows comparative estimates.
1270
The length frequency distributions for the sampled catch are show in Figure 1. Figure 2 shows the spine radius
and fork length relationship. Growth curves for the three methods are shown in Figure 3. Figures 4 to 8 show
plates of fin spine sections with comments on the banding seen. Figure 9 shows the areas where catches and
samples were taken in 2002.
4. Discussion
4.1 Ageing
This study proposes that a year of life results in the formation of a narrow band of opaque appearance. When two
or three opaque bands were observed in a cluster it was most often the case that one of these bands was dominant
with the others appearing less strongly and fading out before becoming fully concentric. These single or double
bands were separated from each other by wider opaque zones. This is in approximate agreement with what has
been described by other workers: González-Garcéz and Fariňa-Perez (1983); Bard and Compeán-Jiminez (1980);
Lee and Yeh (1998); Fernandez (1992); Zarate et al. (2005), and Santiago and Arrizabalaga (2005). Previous
studies suggest that the narrow opaque bands are formed after migration from summer feeding grounds in the
Bay of Biscay and adjacent waters to wintering areas in the wider Atlantic: González-Garcéz and Fariňa-Perez
(1983); Bard and Compeán-Jiminez (1980) and Santiago and Arrizabalaga (2005). Following from these,
incomplete or faint bands were interpreted as checks and evidence of discontinuous transition between slow and
fast growth phases in the annual cycle.
On the smallest fish it was seen that bands could be indistinct or absent, an observation previously made by
González-Garcéz and Fariňa-Perez (1983). In such instances the distance between the edge of the section and the
vascularised core was interpreted as a single translucent band and the product of one year of life. This implies
that the first opaque band is incorporated into the edge of the spine and indicates a need for elucidation of the
physiology and function of fin spines to ensure the correct use and interpretation of this tissue as ageing material.
As observed by Beamish (1981), the clustered annuli seen in older fish infer that growth in length slows down
with age, an understanding complimented by von Bertalannfy growth curves. There are two distinct
understandings of north Atlantic albacore age and growth produced by fin spine ageing studies. In this study it is
proposed that the youngest albacore in the sample were 1 year old and between 47cm and 58cm in length. The
values for length at age 1 estimated in this study are supported by a group of other studies: Compeán-Jiminez
and Bard (1983), Ortiz de Zárate et al. (2005), and Santiago and Arrizabalaga (2005). An alternative fin spine
age estimate is age 2 at around 52cm, González-Garcéz and Fariňa-Perez (1983) and Fernandez (1992). Both of
these studies had access to smaller fish than were available to this study. The use of mackerel braillers in the
trawls from which the samples were taken suggests that there were no smaller fish available from which an
alternative understanding might have been synthesized. For assessment purposes age at length is estimated
statistically and these corroborate the higher length at age 1 fin spine age estimate, Ortiz de Zárate and Restrepo
(2001).
4.2 Von Bertalannfy Growth Parameters
The current study utilizes a greater range of sizes than previous studies of north Atlantic albacore though the
larger fish were thinly spread over a wide range of lengths (n= 21, <120>90). Three methods were used to plot
growth curves and obtain von Bertalannfy parameters chiefly because of uncertainty around the relatively small
numbers of large individuals in the sample. The range of L∞ values for all methods is around 6cm with the
highest value obtained by the Ford Walford method. Solver and bootstrap analysis produce statistically robust
interpretations of the same data with little to choose between the values produced. As growth parameters are
established for a whole population and not just the individuals sampled, the bootstrap was thought to be the most
amenable and exhaustive method available to estimate the influence of a relatively small number of large
individuals on the trajectory of the growth curve and the resultant parameters. The bootstrap estimate of L∞ in
the present study is slightly higher than those reported by the 1980 and 1992 studies of North Atlantic albacore
though around 13cm lower than the 1983 study, a difference which is reflected in the length at age matrix from
that study also. The present study estimates are close to recent spine age estimation results by Santiago and
Arrizabalaga (2005) which have sought to corroborate fin spine ageing with length frequency analysis and
tagging results.
1271
5. Conclusion
The ageing method described here has only been partially validated and to date there have been insufficient
returns of OTC tagged fish to account for all variation described as annuli formation in spine sections. OTC
tagging to date at least supports the annual formation of single, double and triple opaque bands, described in this
and other studies, Ortiz de Zárate et al. (1996). Nonetheless fin spine age estimation would seem to be more
amenable to corroboration than conclusive validation. Even with large-scale tag and recapture programs this is
likely to remain the case because of the low incidence of adult fish in major commercial fisheries, Ortiz de
Zárate et al. (2004). Crowding and obscuring of bands through vascularisation sets a limit on the certainty with
which annuli can be inferred in the very largest fish, making absolute age estimation highly uncertain. The use
of fin spines is based on the ease with which they can be obtained comparative to other tissues such as otoliths or
vertebrae.
The results obtained are in close agreement with recent studies and the ICCAT accepted growth parameters.
They arise from spatially and biologically distinct catches which reflected the seasonal development of the
fishery in 2002: juveniles in the Bay of Biscay in July and August and spent adults on the shelf edge west of
Brittany and Ireland in September and October. This probably simplified the age estimation as it gave rise to two
distinct data sets without the added subtleties of inter-seasonal effects.
Acknowledgements
I would like to thank Maurice Clarke and Paul Connolly and Hans Gerritsen of the Marine Institute for
facilitating me in this work.
Free R software was used for this work and I thank the R Development Core Team and all contributors to the R
project (http://www.R-project.org).
I am especially grateful to the owners and crews of the pelagic trawlers that gave me berths in the 2002 tuna
season.
References
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Sci. Pap. ICCAT, 56(4): 1223-1311.
Beamish, R.J., 1981, Use of fin-ray sections to age walleye pollock, Pacific cod, and albacore, and the
importance of this method. Transactions of the American Fisheries Society 110:287-299.
Cass, Alan J. and Beamish, Richard J. 1983, The first evidence of validity of the fin ray method of age
determination for marine fishes. North American Journal of Fisheries Management. 3: 182-188.
Bard ,F.X. and Compeán-Jiminez, G. 1980, Consequences pour l’évaluation du taux d’exploitation du germon
(Thunnus alalunga) Nord Atlantique d’une courbe de croissance déduite de la lecture des sections de
rayons épinaux. Collect. Vol. Sci. Pap. ICCAT, 9: 365-375.
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Senegal using dorsal fin spine sections. US Department of Commerce, NOAA Technical Report, NMFS
8, 105-110.
Compeán-Jiminez, G and Bard, F.X. 1983, Growth increments on the the dorsal spines of eastern Atlantic
bluefin tuna and their possible relation to migration patterns. U.S. Dep. Commwe., NOAA Tech. Rep.
NMFS 8:77-86.
1272
Fernandez, M. 1992, Revision des methodés d’âgeage du germon (Thunnus alalunga, Bonn. 1788) nord-est
Atlantique par l’étude des piecés anatomiqués calcifieés. Collect. Vol. Sci. Pap. ICCAT, 39: 225-240.
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me=alalunga
Gonzalez-Garcez, A. and Farina-Perez, A.C. 1983, Determining the age of young albacore, Thunnus alalunga,
using the dorsal spines. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 8:117-122.
King, M., 1995.,Fisheries Biology, Assessment and Management. Fishing News Books, Oxford. 121-124.
Lee, L.K. and Yeh, S.Y. 1998, Studies on the age growth of south Atlantic albacore (Thunnus alalunga)
specimens collected from Taiwanese longliners. Collect. Vol. Sci. Pap., ICCAT, 40(2): 354-360.
Ortiz de Zarate, V., Landa, J., Ruiz, M. and Rodriguez-Cabello, C. 2005, Ageing based on spine sections reading
of North Atlantic albacore (Thunnus alalunga): Precision, accuracy and agreement. Collect. Vol. Sci. Pap.
ICCAT, 58(4):1235-1248.
Ortiz de Zarate, V., Megalofonou, P., De Metrio, G. and Rodriguez-Cabello, C. 1996, Preliminary age validation
results from tagged-recaptured fluorochrome label albacore in the north east Atlantic. Collect. Vol. Sci.
Pap. ICCAT, 43: 331-338.
Ortiz de Zarate, V., Parrack, P. and N.C., 1996. Note on updated tag-recapture growth analyses for north Atlantic
albacore tuna. Collect. Vol. Sci. Pap. ICCAT, 43: 247-253.
Ortiz de Zárate, V., and Restrepo, V. 2001, Analysis of tagging data from North Atlantic albacore: von
Bertalanffy growth estimates and catch-at-age. Collect. Vol. Sci. Pap. ICCAT, 52,(4): 1435-1446.
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(Thunnus alalunga) surface fisheries in the north eastern Atlantic in 2002. Collect. Vol. Sci. Pap. ICCAT,
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1273
Table 1. Age length key for trawled albacore 2002. A birthday of the June 1st is assumed (Zaráte et al. 2005).
Age
FL cm
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
total
1
1
2
14
12
10
11
7
3
1
2
1
2
1
1
5
1
4
3
7
4
6
7
5
4
7
1
9
13
1
2
6
2
2
1
3
4
5
Nos. at
Length
6
7
8
1
2
1
3
3
1
1
3
1
3
2
1
2
2
3
4
3
5
8
2
5
1
4
3
4
5
5
3
1
1
1
1
1
4
3
3
2
3
1
1
2
2
2
1
1
1
2
1
1
1
1
1
1
3
1
1
3
2
2
1
1
2
2
1
1
2
41
23
16
17
1274
1
1
4
4
6
4
5
3
3
1
2
4
1
1
1
1
2
2
1
1
92
10
2
15
13
15
12
11
6
8
6
7
7
5
4
7
1
11
14
1
4
8
2
4
1
4
3
1
1
3
4
7
2
3
64
9
1
1
9
9
1
2
1
1
1
1
2
2
1
1
3
276
1
Table 2. Bootstrapped age at length estimates for trawled albacore.
Age
1
2
3
4
5
6
7
8
9
10
lower 95%
49
63
74
83
90
97
102
105
108
111
Mean
50
64
75
84
91
98
103
107
111
114
upper 95%
51
64
76
85
92
99
104
109
113
116
Table 3. Age at length estimates from different studies.
GonzálezCompeánGarcéz and
Santiago and
Jiminez
Fernandez( Zárate et al
FariňaArrizabalaga
and Bard
1992)
(2005)
Perez.
(2005)
(1980)
(1983)
Age
1
2
3
4
5
6
7
8
9
10
length
length
50
39
63
74
84
94
52
62
72
81
89
94
length
length
52
64
73
82
90
96
101
104
108
length
49
48
50
63
76
85
98
102
105
111
111
61
72
82
89
95
101
105
109
112
64
75
84
91
98
103
107
111
114
Table 4. Von Bertalanffy estimates from three methods for trawled albacore.
Growth
Parameters
Linf
K
T0
Present
study
bootstrap
BootstrapMean
Estimate
Bootstrap
lower
95%
Bootstrap
upper
95%
EXCEL
solver
estimate
Ford
Walford
Estimate
127.42
0.190083
-1.6352422
121.17
0.16
-1.86
135.52
0.22
-1.41
127.81
0.19
-1.67
129.07
0.18
-1.86
1275
Table 5. Von Bertalanffy growth estimates and parameters from different studies.
Growth Parameters
Author
Bard (1981)
González-Garcéz and Fariňa-Perez (1983)
Santiago and Arrizabalage (2005)
Present study
Fernandez (1992)
Linf
124.74
140.08
127.07
127.42
128.53
Ortiz de Zarate and Parrack (1996)
108.21
K
0.23
0.13
0.18
0.19
0.17
T0
-0.98
-1.57
-1.62
-1.64
-1.12
Method
Spines
Spines
Spines
Spines
Vertebrae
0.265
1.25
Tagging
200
180
160
120
100
80
60
40
20
0
45
49
53
57
61
65
69
73
77
81
85
89
93
97 101 105 109 113 117
cm
July to August n=1566
September to November n=584
spines n=276
Figure 1. Frequency distributions of length and spine sampled albacore.
Fork length
cm
number
140
140
y = 2.8444x + 19.575
120
R = 0.935
2
100
80
60
40
20
0
0
10
20
30
40
Spine radius mm 10^-1
Figure 2. Relationship of fin spine radius to fork length.
1276
Van Bertalanffy Bootstrapped Growth Curves
140
120
100
cm
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10
11
Years
lower 95%
mean
upper 95%
Log. (mean)
cm
Von Bertalanffy Solver Plot
140
120
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10
11
Years
cm
Ford Wolford von Bertalanffy plot
140
120
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
Years
Figure 3. Von Bertalanffy growth curves with three methods for trawled albacore.
1277
10
11
Figure 4. Section from a 49 cm albacore caught on the 17/8/2002 with very faint banding estimated at 1 year;
section from a 50 cm albacore caught on the same date with distinct double opaque banding also estimated at
year 1.
Figure 5. Two cross sections: the left is from a 65cm from the 14/8/2002 with two opaque autumn winter bands
and corresponding spring summer translucent bands, estimated at 2 years. The right comes from an 81cm
albacore caught on the 20/8/02 estimated to be 3 years with three zones of banding.
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Figure 6. The left section is from an 88cm albacore caught on 19/9/02 showing four distinct opaque autumnwinter bands estimated to be four years old. Year 1 is partially vascularised and appears as a single opaque band.
Year 2 has checks on either side and has the appearance of a triple band; year 3 appears as a double band while
year 4 appears as a single band at the edge of the section. The right section is from a 90cm albacore caught on
the 12/9/02 and shows 5 single opaque bands.
Figure 7. On the left a 100 cm albacore caught on the 23/9/2002 and estimated at 6 years old. The right section
is estimated at 7 years from a 97cm albacore caught on the 16/9/02. In both cases the first and second annuli are
partially obscured by vascularisation.
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Figure 8. The left section is estimated at 8 years from a 104cm albacore caught on the 12/9/02. The right section
is from a 119cm albacore caught on the 20/9/2002 estimated at 10 years and showing single double and triple
opaque bands.
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-10°
-5°
0°
54°
Albacore catch
and sample locations
2002
54°
Albacore numbers
1 - 100
101 - 500
52°
52°
501 - 1500
1501 - 3000
200m_1000m_contours
Depth
50°
50°
-1000 - -900
-899 - -700
-699 - -600
-599 - -400
-399 - -200
48°
48°
46°
46°
44°
44°
42°
42°
-10°
-5°
Figure 9. Sampling and catch locations for albacore in 2002 for pair trawlers.
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