SCRS/2007/139
Collect. Vol. Sci. Pap. ICCAT, 62(5): 1629-1637 (2008)
AGE AND GROWTH OF BULLET TUNA (AUXIS ROCHEI) IN THE
WESTERN MEDITERRANEAN SEA
X. Valeiras1, D. Macías2, M.J. Gómez2, L. Lema2, S. García-Barcelona2,
J.M. Ortiz de Urbina2 and J.M. de la Serna2
SUMMARY
A total of 216 dorsal fin spines from western Mediterranean bullet tuna were analyzed from 2003 to
2006 for ageing and growth studies. The length of the aged individuals ranged from 31 to 44 cm for the
males and from 31 to 46 cm for the females. Fish ages ranged 2 to 5 years old and the mean lengths by
age were calculated for males and females. Growth parameter estimates were calculated from 206 cut
spine sections which provided readable growth annuli by sex. The standard von Bertalanffy growth
function was used to fit length at- age data. The growth parameters based on standard von Bertalanffy
growth function are the following: for males, L (asymptotic length)=43.751 cm, k (growth
coefficient)=0.865, t0 (age at zero length)=-0568; for females, L=45.545 cm, k=0.461, t0=-0.821; for
both sexes, L=44.041 cm, k=0.700 , t0=-0.139. The relationships between FL and dorsal fin spine
diameter were calculated for both sexes. Age-length keys were provided for catch at age calculation
application.
RÉSUMÉ
Un total de 216 épines de la nageoire dorsale de bonitous de l’ouest de la Méditerranée ont été
analysées de 2003 à 2006 aux fins d’études de détermination de l’âge et de croissance. La taille
(longueur à la fourche) des individus dont l’âge avait été déterminé oscillait entre 31 et 44 cm pour les
mâles et entre 31 et 46 cm pour les femelles. L’âge des poissons allait de 2 à 5 ans et les tailles
moyennes par âge ont été calculées pour les mâles et pour les femelles. Les paramètres de croissance
ont été estimés pour les deux sexes à partir de 206 sections d’épines qui ont fourni des anneaux de
croissance lisibles. On a utilisé la fonction de croissance standard de von Bertalanffy pour ajuster les
données de longueur par âge. Les paramètres de croissance basés sur la fonction de croissance
standard de von Bertalanffy sont les suivants : pour les mâles, L (longueur asymptote)=43,751 cm, k
(coefficient de croissance)=0,865, t0 (âge à la taille zéro)=-0568; pour les femelles, L=45,545 cm,
k=0,461, t0=-0,821; pour les deux sexes, L=44,041 cm, k=0,700 , t0=-0,139. Les relations entre FL et
le diamètre de l’épine de la nageoire dorsale ont été calculées pour les deux sexes. Des clefs âge-taille
ont été fournies pour le calcul de la prise par âge.
RESUMEN
Se analizaron un total de 216 espinas de la primera aleta dorsal de melva del Mediterráneo occidental
muestreadas entre 2003 y 2006 para realizar estudios de edad y crecimiento. Las tallas (longitud a la
furca) comprendieron entre los 31 y 44 cm para los machos, y entre los 31 y 46 cm para las hembras. El
rango de edad de los peces analizados estuvo entre 2 y 5 años y se determinaron las tallas medias por
edad. Los parámetros de crecimiento se estimaron para ambos sexos a partir de 206 secciones de
espina que proporcionaron bandas de crecimiento legibles. Se utilizó la función de crecimiento
estándar de von Bertalanffy para ajustar los datos de talla por edad. Los parámetros de crecimiento
basados en la ecuación estándar de von Bertalanffy son los siguientes: para machos, L  (longitude
asintótica)=43.751 cm, k (coeficiente de crecimiento)=0.865, t0 (edad a la talla cero)=-0568; para
hembras, L=45.545 cm, k=0.461, t0=-0.821; para ambos sexos, L=44.041 cm, k=0.700 , t0=-0.139 .
Se calcularon las relaciones diametro de la espina y FL para ambos sexos. Se presentan las claves
tallas-edad para el cálculo de capturas por edad.
KEYWORDS
Bullet tuna, age determination, growth curves, Mediterranean, trap
1
2
Instituto Español de Oceanografía, P.O. Box 240, 39080 Santander, Spain.
Instituto Español de Oceanografía, P.O. Box 285, 29640 Málaga, Spain.
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1. Introduction
The genus Auxis distributes worldwide in tropical and subtropical waters. Bullet tuna (Auxis rochei) is an epi
and meso-pelagic fish that has a seasonal coastal distribution in temperate and tropical areas including the
Mediterranean (Uchida, 1981; Collete, 1986; Valeiras and Abad, 2007). This species is abundant in the Strait of
Gibraltar, north coast of Africa and Spanish Mediterranean coast (Postel, 1973). The bullet tuna is one of the
most abundant small tuna species in the Spanish Mediterranean Sea where has been commercially exploited by
seasonal artisanal fisheries (Sabatés and Recasens, 2001). In Spain, the species have been caught traditionally by
seasonal coastal fisheries. Several fishing gears have been used to catch it: Traps and other minor fixed gears,
purseseine and hand-line (Uchida, 1981).
Little is currently known about the biology of this small tuna in the Western Mediterranean Sea. Certain areas in
the Mediterranean have been suggested as possible spawning sites of Auxis sp: Greece and Gulf of Catania
(Bellot, 1954), Balearic Islands (Duclerc et al., 1974), Tunisian and Algerian waters (Postel, 1964) and off east
Spanish Mediterranean coasts (Macías et al., 2005). The spawning period in the Mediterranean has been reported
to occur from June to September (Ehrenbaum, 1924; Piccinetti et al., 1996; Alemany, 1997; Macías et al., 2005).
The first maturity size has been stated in 35 cm (FL) when the fish is two years old (Rodriguez-Roda, 1983).
Information concerning to migration patterns is scarce and fragmented (Rey and Cort, 1981). Several authors
have suggested a genetic migration from the Atlantic Ocean to the spawning areas in the Mediterranean trough
the Gibraltar Strait (Sabatés and Recasens, 2001).
Knowledge of the early life stages in tunas is very scarce. It is assumed that larval period is short. During the
first life stages bullet tuna are not caught and juvenile life history is unknown. Inmature fish first appear in
fishery from around 25 cm of fork length. Bök and Oray (2001) studied age and growth by otoliths and dorsal
spines analysis in the eastern Mediterranean and Rodriguez-Roda (1983) studied bullet tuna age composition
from Atlantic area near Gibraltar Strait.
From 2003, sampling effort in a Spanish tuna trap was focused on collect bullet tuna samples to improve
biological knowledge in western Mediterranean. The aim of this paper is to present first results from the western
Mediterranean Sea fisheries from spine analysis and provide age-length keys and parameter estimates of bullet
tuna growth in the area.
2. Material and methods
2.1 Fish sampling
216 specimens were collected from tuna trap of “La Azohía” at Mediterranean coast of Spain during sampling
from 2003 to 2006. Sampling was done according to a random stratified design covering the length range of the
species in the study area. Size FL (fork length in cm) and sex were recorded from all sampled specimens.
2.2 Spine preparation
Methodology for spine analysis was based on Ortiz de Zárate et al. (2007). The first spine of the first dorsal fin
was collected from each specimen. The spine was preserved in a dry state within a paper envelope and labelled.
The spine was cut near to the base coinciding with the bulge in the spine (the part with the greatest diameter) and
close to the ridge. Series of spines were encased in a matrix of plastic resin. A cross section of 0.5 mm thick was
cut using an ISOMED 5000 Cutter. Two consecutive cuts were made in order to choose the best one when taking
the reading. The sections were washed in a 70% ethanol solution. They were later mounted onto labelled holders
and embedded in Eukitt highly transparent mounting resin.
2.3 Age interpretation
The clearest of the two sections was examined using a binocular microscope with transmitted light at 80x. The
diameter of each growth band (annulus) was measured and recorded. Spine sections were read twice by one
reader and unresolved differences in readings resulted in spine elimination. Alternative pairs of a translucent
band and a opaque band were considered to be a year annuli. When present, multiple annuli and disappearance
of the first annulus in older fish were carefully considered to assess the age classes.
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2.4 Growth parameters
Age length keys were produced for males, females and for the two sexes combined, and their mean lengths at
age and standard deviations calculated.
Von Bertalanffy growth curves were fitted to the data applying the standard von Bertalanffy growth function
(von Bertalanffy, 1938). Growth parameters were computed for females and males using non-linear least square
estimation.
Standard VB model: Lt= L (1-e-k(t-t0))
where,
Lt is length (FL) at age t;
L is asymptotic length;
k is the growth coefficient;
t0 is theoretical age at zero length.
2.5 Backcalculation
The relationship between FL and dorsal spine diameter (S) was determined by using two procedures:
− Standard linear regression: FL = a+bS
− Power function: FL=aSb
3. Results and discussions
A total of 206 sections of first dorsal spines were aged successfully (109 males and 97 females). 10 spines were
unreadable due to multiple banding pattern or unidentifiable growth annuli. A summary of samples collected for
this work is presented in Table 1.
Mean sizes by age for both sexes are presented in Table 2. Assigned ages of spine sections were from 2 to 5
years. 75% of males and 68% of females were 2-3 years old. Age length key is presented in Table 3.
Growth parameter estimates for the standard von Bertalanffy are presented in Table 4. Equations results were
the following:
Standard VB model:
Males: Lt= 43.751 (1-e-0.865(t+0.568))
Females: Lt= 45.545 (1-e-0.461(t+0.821))
Both sexes: Lt= 44.041 (1-e-0.700(t+0.139))
In Figure 1, growth curves of observed lengths at age data and von Bertalanffy estimates are plotted. Also
growth curves from results of other authors are included. Mean FL at age for present paper and other articles are
presented in Table 5 (Atlantic and eastern Mediterranean Sea).
The obtained relationship between FL and anal fin spine radius were the following (Figure 2):
Linear regression relationship:
Males: FL = 10.746S+20.053, r 2=0.7781.
Females: FL = 10.743S+20.326, r 2=0.7227.
All sexes: FL = 10.714S+20.233, r 2=0.7529.
Power function relationship:
Males: FL = 29.932S 0.471, r 2=0.7674.
Females: FL = 30.445S 0.4485, r 2=0.7134.
All sexes: FL = 30.181S 0.4602, r 2=0.7425.
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Figure 3 presents bullet tuna annual size distributions from 2003 to 2005 (Macías et al., 2006). All annual
distributions show a bimodal appearance. The highest modal value approximately corresponds to 35-36 cm (2
years old tunas). A second (minor) modal value was around 44 cm except for 2005 when this modal value cannot
be found (All sampled fish were around two-year old size). The second modal value could be compounded by 3
years old and older specimens.
Bök and Oray (2001) studied age and growth by otoliths and dorsal spines analysis and found five age groups
(0+ to 4+) for the Aegean Sea and the eastern Mediterranean. Rodriguez-Roda (1983) studied vertebrae of 27
bullet tuna from Atlantic area near Gibraltar strait and found four age groups (1-4).
In this work, we obtain similar results on growth parameters and mean lengths at age of bullet tuna in western
Mediterranean compared to north Atlantic (Gibraltar Strait) and eastern Mediterranean Sea estimates.
Acknowledgements
The authors would like to thank the skippers and crew members of the Spanish trap of “La Azohía” for their
collaboration on this and other scientific tasks. Special thanks to all the staff involved in the IEO-Málaga
projects PNDB-Túnidos and GPM3 through which this research and other works were possible. We are very
grateful to Joaquín Barrado for his assistance in laboratory work and to Marta Ruiz from Tuna growth laboratory
at Santander.
References
ALEMANY, F. 1997. Ictioplancton del Mar Balear. Ph. D. thesis, Univ. Illes Balears.
BELLOC, G. 1955. Les thons de la Méditerranée. Deuxième note: Thonine et Bonite. FAO Proc. Gen. Fish.
Counc. Medit. nº 3 (52): 471-486.
BÖK, T. and K. Oray, 2001. Age and growth of bullet tuna Auxis rochei (Risso, 1810) in Turkish waters. Col.
Vol. Sci. Pap. ICCAT, 52(2): 708-718.
COLLETE, B.B. 1986. Scombridae. In: P.J.P. Whitehead, M.-L. Bauchot, J.-C. Hureau, J. Nielsen, and E.
Tortonese (eds.), Fishes of the Northeastern Atlantic and the Mediterranea. Vol II. pp. 981-997.
UNESCO, Paris.
DUCLERC, J., J. Sacchi, C. Piccinetti, G. Manfrin, A. Dicenta, and J-M. Barrois. 1974. Nouvelles données sur
la reproduction du thon rouge, Thunnus thynnus (Linnaeus), et d’autres espèces de Thonidés en
Mediterraneé. Rev. Trav. Inst. Pêches Maritime., 37: 163-176.
EHRENBAUM, E. 1924. Scombriformes. Report on the Danish Oceanografical Expeditions 1908-1910.
Mediterranean and Adjacent Seas, 2 (A, 11).
MACÍAS, D., M.J. Gómez-Vives, J.M. de la Serna. 2005 . Some reproductive aspects of bullet tuna (Auxis
rochei) from the south western Spanish Mediterranean. Collect. Vol. Sci. Pap. ICCAT, 58(2): 484-495.
MACÍAS, D., L. Lema, M.J. Gómez-Vives, J.M. Ortiz de Urbina, and J.M. de la Serna. 2006. Some biological
aspects of small tunas (Euthynnus alletteratus, Sarda sarda & Auxis rochei) from the south western
Spanish Mediterranean traps. Collect. Vol. Sci. Pap. ICCAT, 59(2): 579-589.
ORTIZ DE ZÁRATE, V., X. Valeiras and M. Ruiz, 2007. Sampling protocol for skeletal structures of north
Atlantic albacore tuna (Thunnus alalunga) and ageing interpretation. Collect. Vol. Sci. Pap. ICCAT,
60(2): 492-506.
PICCINETTI, C., Piccinetti, G. Manfrin, and S. Soro. 1996. Larve di Tunnidi in the Mediterranean. Biol. Mar.
Medit., 3: 303-309.
POSTEL, E. 1973. Thunnidae. Check – list of the fishes of the north-eastern Atlantic and of the Mediterranean.
Clofnam I. Editors: J.C. Hureau and Th. Monod, Paris. UNESCO.
RODRÍGUEZ-RODA, J. 1983. Edad y crecimiento de la melva, Auxis rochei (Risso), del Sur de España. Invest.
Pesq. (Barc.), 47 (3): 397-402.
SABATÉS, A. and L. Recasens. 2001. Seasonal distribution and spawning of small tunas, Auxis rochei (Risso)
and Sarda sarda (Bloch) in the northwestern Mediterranean. SCI. Mar., 65 (2): 95-100.
1632
UCHIDA, R.N. 1981. Synopsis of biological data on frigate tuna, Auxis thazard, and bullet tuna, A. rochei.
NOAA Tech. Rep. NMFS Circ., (436):63 p. Issued also as FAO Fish.Synop., (124):63 p.
VALEIRAS, J. and E. Abad, 2007. ICCAT Manual. Chapter 2. Description of Species. 2.1 Species Directly
Covered by the Convention. 2.1.11. Small tuna (in press).
Table 1. Summary of bullet tuna from western Mediterranean Sea used in this study (M, males; F, females; I,
indeterminate).
Number
Size range cm)
Age range (years)
M
111
31-44
2-5
F
105
31-46
2-5
M+F+I
216
31-46
2-5
Table 2. Summary statistics of male and female aged bullet tuna from western Mediterranean Sea. FL: furcal
length in cm.
Age_Males
2
3
4
5
n spines
62
21
19
7
Mean FL
35.0
39.5
42.4
41.7
FL range
31-39
36-43
39-44
39-44
Std. Error
0.23
0.44
0.34
0.75
Age_Females
2
3
4
5
n spines
53
19
22
3
Mean FL
35.2
38.9
41.0
43.0
FL range
31-38
35-42
39-44
42-45
Std. Error
0.23
0.35
0.38
1.00
Age_Males+Females n spines
2
115
3
40
4
41
5
10
Mean FL
35.1
39.2
41.7
42.1
FL range
31-39
35-43
39-44
39-45
Std. Error
0.16
0.29
0.28
0.60
Table 3. Age length key (ALK) of bullet tuna from western Mediterranean Sea.
FL
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
2
100
100
100
100
96
93
80
69
7
3
4
4
7
20
31
61
57
29
25
17
32
71
58
58
89
1633
5
43
17
25
11
100
Table 4. Parameter estimates for the standard von Bertalanffy for bullet tuna from western Mediterranean Sea
(n= 111 males and 105 females).
Growth
Parameters
Standard von Bertalanffy
Male
Female
All sexes
L∞
43.751
45.545
44.041
k
t0
0.865
-0.568
0.461
-0.821
0.700
-0.139
Table 5. Estimated size at age for bullet tuna from studies in the Atlantic and Mediterranean.
Age
BUL
1
2
3
4
5
Bök and Oray,
2001
East
Mediterranean
30.7
34.4
38.7
41.1
42.4
Rodriguez-Roda,
1983
Gibraltar
25
33.1
37.4
41.2
This paper
This paper
Observed
vonBertalanffy
West
West
Mediterranean Mediterranean
24.2
35.1
34.2
39.2
39.1
41.7
41.6
42.1
42.8
45
40
FL (cm)
35
30
25
20
15
1
2
3
4
5
6
Age (yr)
Bök and Oray, 2001
Rodriguez-Roda, 1983
Valeiras et al., 2007 (VB)
Valeiras et al., 2007 (obs)
Figure 1. Growth curves for this paper (observed and von Bertalanffy model) and curves from Bök and Oray
(2001) and Rodriguez-Roda (1983).
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Males
60
55
50
FL (cm)
45
40
y = 10.746x + 20.053
R2 = 0.7781
35
30
y = 29.932x 0.471
R2 = 0.7674
25
20
15
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.4
2.6
Spine diameter (mm)
Females
60
55
50
FL (cm)
45
40
35
y = 10.743x + 20.326
R2 = 0.7227
30
y = 30.445x 0.4485
R2 = 0.7134
25
20
15
1
1.2
1.4
1.6
1.8
2
2.2
Spine diameter (mm)
Males + Females
60
55
50
FL (cm)
45
40
y = 10.714x + 20.233
R2 = 0.7529
35
30
y = 30.181x 0.4602
R2 = 0.7425
25
20
15
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
Spine diameter (mm)
Figure 2. Relationship between FL and dorsal spine diameter for male, female and both sexes bullet tuna from
the western Mediterranean Sea.
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Figure 3. Bullet tuna annual size distributions from 2003 to 2005 and the combined size distribution. Extracted
from Macías et al., 2006.
1636
Figure 4. Bullet tuna spine sections examples. A: age 2, B: age 3, C: age 4, D: age 5 (Not proportional sizes of
spine pictures).
1637