Reproductive potential of yellowfin tuna (Thunnus albacares) in the western Indian Ocean

Reproductive potential of yellowfin tuna (Thunnus albacares) in the western Indian Ocean

Year of publication 2013

Product type Document

Edition 1

Synopsis (short abstract) The reproductive biology of Yellowfin Tu (Thunnus albacares) in the western Indian Ocean was investigated from samples collected in 2009 and 2010. In our study, 1012 female Yellowfin Tu 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 seasolity, fish condition, and fecundity. The length at which 50% of the female Yellowfin Tu population matures (L50) was estimat ed at 75 cm in fork length (FL) when the maturity threshold was established at the cortical alveolar stage of oocyte development. To eble comparison with previous studies, L50 also was estimated with maturity set at the vitellogenic stage of oocyte development; this assessment resulted in a higher value of L50 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 Tu 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 oo cytes per gram of god-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 Tu in the western Indian Ocean.

Meeting Session Number 15

Language English

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Fecundity regulation strategy of the yellowfin tuna (Thunnus albacares) in the Western Indian Ocean 2013

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The oocyte development process and fecundity regulation (i.e. whether yellowfin tu shows determi- te or indetermite fecundity) were alyzed to investigate the reproductive strategy of yellowfin tu, Thunnus albacares. A total of 819 yellowfin ovaries were sampled at sea and at the Seychelles cannery dur- ing 2009 and 2010 from purse-seiners operating in the Western Indian Ocean. Histological alysis and automated computer-controlled image alysis software were used to study four main criteria applie d for fecundity style determition: (a) oocyte size–frequency distribution, (b) number of cortical alveoli and total vitellogenic oocytes in different ovary maturation phases, (c) differences in mean diameter of tertiary vitellogenic oocytes, and (d) seasol development of atresia. The results revealed an asynchronous oocyte development and a continuous oocyte size–frequency distribution throughout all ovarian developmental phases over the spawning season. The percentage and number of cortical alv eoli and total vitellogenic oocytes remained constant through the spawning season. The mean diameter of tertiary vitellogenic oocytes decreased as spawning progressed. Also, the incidence of atresia was higher at the end of the spawning season as a consequence of over-recruitment of oocytes during this period. These findings revealed that yellowfin tu exhibit indetermite fecundity.
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Traditional small scale fishing for yellowfin tuna Thunnus albacares in Andhra Pradesh along east coast of India 2013

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The yellowfin tus form one of the major components of oceanic tu catch along the Indian coast. They are fished both along the mainland as well as the Island systems with the total annual catch from the mainland varying from 10,307 t to 19,163 t during 2010-2012. Commercial fishing is mainly by small mechanized wooden crafts and non-mechanized traditiol crafts. Mechanized crafts operated pole and line, long line and gillnets and non- mechanized crafts operated hand lines and troll lines. Highly s killed fishermen of Andhra Pradesh State situated along the east coast of India use traditiol catamarans fitted with sails to catch yellowfin tus from deep waters by operating either the hand lines or the troll lines. Around 1500 such units operated along the coast with an average annual landings of 4,300 t during 2010-2012. Fishing is carried out for a day as the crafts do not have any storage facility. Peak landings are during October–January followed by May-July. The annual catch per unit at Visakhapatm was 58 kg and during the peak fishing season it increased to 71 kg per unit. The fork length of the yellowfin ranged from 20 to 185 cm with the mean at 130 cm. Fishes above 80 cm were found to be mature and the size at first maturity was estimated to be between 85 and 90 cm. Males were domint with a male: female ratio of 1: 0.53. The length- weight relationship is W= 0.017077L 2.976. Feeding habit of yellowfin tu indicated the fish to be a nonselective generalist feeder, foraging on micronektonic pelagic or benthic organisms available in the epipelagic waters. Teleost fish, crabs, squids and shrimps were the major food items. Age and growth were estimated using length based methods. The von Bertalanffy growth parameters estimated were L∞ = 197.42 cm, annual K= 0.30 and t0= -0.1157. Mortality estimates were M= 0.48 and Z= 0.71 and F= 0.23 with the exploitation ratio E= 0.32. Growth was rapid during the initial years when the annual growth increments was as high as 36.6 cm du ring the first year then declined to as low as 3.3 cm in the tenth year. The fish attained a fork length of 56.2 cm at the end of one year. Size at maturity (87.5 cm) corresponded to an age of 1.7 years and the oldest individual in the sample was 9+ years (186 cm). The annual mean lengths varied from 80.6 cm to 115.3 cm with an average mean length of 101.9 cm. The fishery comprised of mostly adults with 64% comprising of fishes larger than size at first maturity.
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Population structure and reproduction of bigeye tuna (Thunnus obesus) in Indian Ocean at western part of Sumatra and southern part of Java and Nusa Tenggara 2013

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This research was conducted to identify population structure and reproduction aspect of big eye tu (Thunnus obesus) in west off Sumatra and south off Java and Nusa Tenggara of Indian Ocean. The sample of fish was collected from catch landed by fishermen. The fish was caught from the Indian Ocean during 2010. Alysis of population structure was done by using of histology technique of fish genetic and reproduction. Result showed that population structure of the big eye tu in Indian Ocean consisted of two different sub populations mely sub population in west off Sumatra and another one is sub population in south of Java and Nusa Tenggara waters. The most of bigeye tu catch (about 39%) was categorized as immature fish with God Somatic Index stage I. The immature fish was mostly found in west off Sumatra waters. While the catch in south off Java and Nusa Tenggara waters was mostly categorized as mature fish. It was indicated that south off Java and Nusa Tenggara waters was as spawning ground of the big eye tu.

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