Reproductive potential of Yellowfin Tuna (Thunnus albacares) in the western Indian Ocean

Abstract

Abstract-The reproductive biology of Yellowfin Tuna (Thunnus albacares) in the western Indian Ocean was investigated from samples collected 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 Seychelles cannery. We assessed the main biological parameters that describe reproductive potential: maturity, spawning seasonality, fish condition, 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 alveolar 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 assessment resulted in a higher value of L 50 at 102 cm FL. The main spawning season, during which asynchrony in reproductive timing among sizes was observed, was November-February 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 skipspawning periods were observed among small females. The Yellowfin Tuna followed a "capital-income" breeder strategy during ovarian development, by mobilizing accumulated energy while using incoming 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.Knowledge of reproductive traits is important for understanding population dynamics, including a population's resilience to fi shing (Schaefer, 2001;Murua and Motos, 2006;Morgan et al., 2009). As alternatives to the traditional spawning stock biomass (SSB), reproductive potential indices have been proposed in which basic reproductive parameters are included as important factors that affect population productivity (Trippel, 1999;Morgan et al., 2009). These parameters include sex-ratio, the age and size of females, maturation ogive, fecundity, fi sh condition, and reproductive history. Inclusion of these biological parameters allows integration of fl uctuations in a population's reproductive success into the assessment and management processes, in addition to estimation of spawning stock biomass (SSB) Murua et al., 2010). Hence, to improve the assessment and management of stocks, it is necessary to increase the quality and quantity of the basic reproductive data used to estimate these reproductive parameters .Yellowfin Tuna (Thunnus albacares) is one of the major target species of the tuna fi shery in the Indian Ocean. Total annual catch of Yellowfi n Tuna in the Indian Ocean has increased signifi cantly, since the early 1980s, with the advent of the purseseine...

Reproductive Biology of Albacore Tuna (Thunnus alalunga) in the Western Indian Ocean

“…Previous studies have suggested that larger and older female albacore have a longer spawning period [24]. This difference has also been observed in yellowfin tuna [67], skipjack tuna [74], and swordfish [75]. …”

“…The observation of POFs in ovaries of fish from region C was an additional indication of recent spawning activity [66]. The spawning period corresponded to waters with seawater temperatures above 24°C at the latitudes 10–30°S as previously reported for albacore and other tuna species [17,19,67]. The lower I G (<1.5) observed in October and January could be related to lower spawning activity at the start and at the end of the spawning season as a result of an asynchrony in spawning at the population level.…”

Biology, fishery, conservation and management of Indian Ocean tuna fisheries

“…Besides the description of different oocytes developmental stages, some preliminary results that could be compared with previous studies have been obtained. Zudaire et al (2010) studied the reproductive biology of the yellowfin of the western Indian Ocean. The sex ratio of yellowfin was 1:0.9 (F:M), and varied from 1:0.2 to 1:3.…”

“…This pattern has been described for yellowfin in different oceans (Fonteneau 2002) and similar percentages were obtained for other tuna species (Sun et al 2005;Marsac et al 2006). Size at first maturity was estimated at 77.8 cm, mean batch fecundity of 2.5 million oocytes and the mean relative batch fecundity of 61.9 oocytes per gram of body weight was calculated by Zudaire et al (2010). Farley et al (2003) reported the sex ratio of bigeye from longliner that found the proportion of males to be more than females (1.24:1) in the Coral Sea, while the sex ratio in other areas in western Australia, southern Indonesia waters revealed the proportion to be about 1:1.…”

Estimation of Yellowfin Tuna Production Landed in Benoa Port With Weight-Weight, Length-Weight Relationships and Condition Factor Approaches

“…There was steep declining of relative condition factor (K n ) when fish reach 106-110 cm to 0.83. This decreased probably related with the reproduction strategies of yellowfin tuna which reach their length at 50% maturity (L 50 ) at 102 cm (Zudaire et al, 2013), 105 cm (Itano, 2000), 105 cm for male and 110 cm for female (Nootmorn et al, 2005) and 110-115 (Hassani & Stequert, 1991).…”