Reproductive Dynamics and Potential Annual Fecundity of South Pacific Albacore Tuna (Thunnus alalunga)

Abstract

The reproductive biology of albacore tuna, Thunnus alalunga, in the South Pacific Ocean was investigated with samples collected during broad-scale sampling between 2006 and 2011. Histology was done in a single laboratory according to standard protocols and the data analysed using generalized linear mixed-effects models. The sex ratio of albacore was female biased for fish smaller than approximately 60 cm FL and between 85 and 95 cm, and progressively more male biased above 95 cm FL. Spawning activity was synchronised across the region between 10°S and 25°S during the austral spring and summer where sea surface temperatures were ≥24 °C. The average gonad index varied among regions, with fish in easterly longitudes having heavier gonads for their size than fish in westerly longitudes. Albacore, while capable of spawning daily, on average spawn every 1.3 days during the peak spawning months of October to December. Spawning occurs around midnight and the early hours of the morning. Regional variation in spawning frequency and batch fecundity were not significant. The proportion of active females and the spawning fraction increased with length and age, and mature small and young fish were less active at either end of the spawning season than larger, older fish. Batch fecundity estimates ranged from 0.26 to 2.83 million oocytes with a mean relative batch fecundity of 64.4 oocytes per gram of body weight. Predicted batch fecundity and potential annual fecundity increased with both length and age. This extensive set of reproductive parameter estimates provides many of the first quantitative estimates for this population and will substantially improve the quality of biological inputs to the stock assessment for South Pacific albacore.

Demographic Structure, Sex Ratio and Growth Rates of Southern Bluefin Tuna (Thunnus maccoyii) on the Spawning Ground

“…Sex ratios reported for other tuna species are generally 1∶1 with a similar prevalence of males in the larger length classes [25]. The male dominance in large length classes for SBT may be due to the observed sexual dimorphism in growth, as suggested for albacore tuna ( Thunnus alalunga ) in the South Pacific Ocean [26].…”

Impact of Climatic Factors on Albacore Tuna <i>Thunnus alalunga</i> in the South Pacific Ocean

“…Dufour [20] showed that the feeding migration of the offshore longitudinal distribution of albacore tuna in the Bay of Biscay was related to the warmer 17˚C isotherm longitude from 1967 to 2005. Farley [41] showed that the peak spawning of albacore tuna in the South Pacific Ocean occurred from October to December [43]. PWI most likely affects the prey abundance and distribution as well as the spawning stages for the younger portion of the albacore tuna stock harvests in the South Pacific Ocean where major part of the harvested stock ranges from 2 to 4 years olds [23].…”

Seasonal oceanography from physics to micronekton in the south-west Pacific

“…Although much of this variability remains unexplained, tuna abundance in space and time has been correlated with factors including oceanographic conditions, physiological constraints (e.g. temperature, depth, oxygen requirements), forage availability, and reproductive behavior (Farley et al, 2013;Senina et al, 2008;Young et al, 2011).…”