252 
Abstract— The reproductive biology 
of Yellowfin Tuna ( Thunnus alba- 
cares) in the western Indian Ocean 
was investigated from samples col- 
lected in 2009 and 2010. In our 
study, 1012 female Yellowfin Tuna 
were sampled: 320 fish on board a 
purse seiner and 692 fish at a Sey- 
chelles cannery. We assessed the 
main biological parameters that de- 
scribe reproductive potential: matu- 
rity, spawning seasonality, fish con- 
dition, and fecundity. The length at 
which 50% of the female Yellowfin 
Tuna population matures (L 50 ) was 
estimated at 75 cm in fork length 
(FL) when the maturity threshold 
was established at the cortical al- 
veolar stage of oocyte development. 
To enable comparison with previous 
studies, L 50 also was estimated with 
maturity set at the vitellogenic stage 
of oocyte development; this assess- 
ment resulted in a higher value of 
L 50 at 102 cm FL. The main spawn- 
ing season, during which asynchrony 
in reproductive timing among sizes 
was observed, was November-Feb- 
ruary and a second peak occurred 
in June. Smaller females (<100 cm 
FL) had shorter spawning periods 
(December to February) than those 
(November to February and June) of 
large individuals, and signs of skip- 
spawning periods were observed 
among small females. The Yellowfin 
Tuna followed a “capital-income” 
breeder strategy during ovarian 
development, by mobilizing accu- 
mulated energy while using incom- 
ing energy from feeding. The mean 
batch fecundity for females 79-147 
cm FL was estimated at 3.1 million 
oocytes, and the mean relative batch 
fecundity was 74.4 oocytes per gram 
of gonad-free weight. Our results, 
obtained with techniques defined 
more precisely than techniques used 
in previous studies in this region, 
provide an improved understanding 
of the reproductive cycle of Yellowfin 
Tuna in the western Indian Ocean. 
Manuscript submitted 7 September 2012. 
Manuscript accepted 20 May 2013. 
Fish. Bull. 111:252-264 (2013). 
doi 10.7755/FB. 111.3.4 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necesarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Reproductive potential of Yellowfin Tuna 
( Thunnus albacares ) in the western Indian 
Ocean 
Iker Zudaire (contact author ) 1 
Hilario Murua 1 
Maitane Grande 1 
Nathalie Bodin 2 
Email address for contact author: iker.zuda@gmail.com 
1 Marine Research Division 
AZTI-Tecnalia 
Herrera Kaia 
Portu aldea z/g 
201 10 Pasaia, Spain 
2 CRH 
UMR 212 EME 
Institut de Recherche pour le Developpement 
Av Jean Monnet 
BP 171 
34203 Sete, France 
Knowledge of reproductive traits is 
important for understanding popu- 
lation dynamics, including a popula- 
tion’s resilience to fishing (Schaefer, 
2001; Murua and Motos, 2006; Mor- 
gan et al., 2009). As alternatives to 
the traditional spawning stock bio- 
mass (SSB), reproductive potential 
indices have been proposed in which 
basic reproductive parameters are 
included as important factors that 
affect population productivity (Trip- 
pel, 1999; Morgan et ah, 2009). These 
parameters include sex-ratio, the age 
and size of females, maturation ogive, 
fecundity, fish condition, and repro- 
ductive history. Inclusion of these 
biological parameters allows integra- 
tion of fluctuations in a population’s 
reproductive success into the assess- 
ment and management processes, in 
addition to estimation of spawning 
stock biomass (SSB) (Murua and 
Saborido-Rey, 2003; Murua et al., 
2010). Hence, to improve the assess- 
ment and management of stocks, it 
is necessary to increase the quality 
and quantity of the basic reproduc- 
tive data used to estimate these re- 
productive parameters (Korta, 2010). 
Yellowfin Tuna ( Thunnus alba- 
cares) is one of the major target spe- 
cies of the tuna fishery in the Indian 
Ocean. Total annual catch of Yellow- 
fin Tuna in the Indian Ocean has in- 
creased significantly, since the early 
1980s, with the advent of the purse- 
seine fishery. Average annual catch 
reached 473,896 metric tons (t) be- 
tween 2003 and 2006 but decreased 
in 2007 and 2008 to around 320,000 
t; in 2011, total annual catch was 
around 300,000 t (IOTC 1 ). 
The Yellowfin Tuna is a batch- 
spawner with asynchronous ovary 
organization (Schaefer, 2001) and 
indeterminate fecundity (Zudaire et 
al., 2013). This species can spawn 
with a frequency of around 1.5 days 
(McPherson, 1991; Schaefer, 2001) 
over a vast area of the tropical zone 
throughout the year (Itano 2 ; Stequert 
et ah, 2001). Its spawning events, as 
with other tuna species, occur in rela- 
1 IOTC (Indian Ocean Tuna Commission). 
2012. Report of the fifteenth session of 
the IOTC Scientific Committee. Victoria, 
Seychelles. IOTC Secretariat, P.O. Box 
1011, Victoria, Seychelles. 
