Reproductive biology of Bigeye Tuna, Thunnus obesus, (Scombridae) in the eastern and central tropical Pacific Ocean

Abstract

Understanding the reproductive potential of any species is of great importance for resource assessment and management. We studied the reproductive biology of Bigeye Tuna, Thunnus obesus, based on 1283 samples taken from the Chinese longline vessels in the eastern and central Tropical Pacific Ocean during February through November 2006. The female-male ratio was 1.0 : 1.5 and males were predominant in all length classes except for the length class of 166-170 cm (fork length). Males dominated in sizes larger than 171 cm, all specimens of 192 cm or larger were males. The main spawning period of Bigeye Tuna was between March and November. Gonadosomatic rates of males were larger than those of females. Statistically, female and male Bigeye Tuna had no significant reproductive seasonality. The observed minimum length at sexual maturity for female Bigeye Tuna was 94 cm. Length at 50% sexual maturity of female Bigeye Tuna was estimated at 107.8 cm, and maturation rate was 0.106 cm −1 . The results derived in this study provide the information critical to our understanding of key life history parameters of Bigeye Tuna in tropic Pacific Ocean.

Vertical behavior of bigeye tuna (Thunnus obesus) in the northwestern Pacific Ocean based on archival tag data

“…a). The proportion of characteristic behavior increased with fish size, being dominant for 65–70 cm FL (age 1, based on growth curve by Zhu et al ., ) (59%), which coincides with the size at which the mean duration of this behavior increases (Fig. b).…”

“…The length of the fish at recapture was used to calculate the change in length, assuming a constant growth rate because growth rate for <100 cm FL fish seems almost constant based on the growth curve by Zhu et al . () and seasonality of growth cannot be expressed based on that study. If length at recapture was not available, a length was estimated based on the length at release, and with comparison of other fish in the present study of similar size, in the same season with a similar number of days at liberty.…”

“…A total of 210 individuals (146 in the Nansei Islands and 64 offshore central Honshu) ranging from 42 to 111 cm FL (age 0.6–2.9 years based on the growth curve by Zhu et al ., ) (Fig. ) were released with archival tag in place during 2000–2010, and 36 (17.1%) individuals were recaptured mainly by handline, pole‐and‐line and troll and partly by longline and purse seine fisheries.…”

“…Bigeye tuna ( Thunnus obesus ) is mainly distributed throughout the three tropical oceans with some extension into temperate areas, and is assumed to spawn throughout tropical and subtropical areas (Nishikawa et al ., ). Size at 50% maturity for females is estimated at 107.8 cm fork length (FL; Zhu et al ., ), corresponding to age 2.6 years based on the growth curve of Zhu et al . ().…”

Reproducción del atún de aleta negra <i>Thunnus atlanticus</i> (Perciformes: Scombridae) en el Archipiélago San Pedro y San Pablo, Atlántico Ecuatorial, Brasil

“…Studies with Bigeye tuna and Yellowfin tuna in the Pacific Ocean reported significant differences between the sexes, and males once again predominated. This suggests that the distinction between the number of males and females may also be related to the selectivity of the several fishing gear types used to catch these individuals in different regions of the ocean (Schaeffer 2001, Zhu et al 2010. Polygamy behavior during spawning is another hypothesis to explain the male biased sex ratio.…”