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

Jessica H. Farley,Simon J. Nicol,Campbell R. Davies,Ashley J. Williams,Simon D. Hoyle,Fausto Tinti

doi:10.1371/journal.pone.0060577

Jessica H. Farley, Simon J. Nicol + Show 4 more

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https://doi.org/10.1371/journal.pone.0060577

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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.

Highlights

Albacore tuna, Thunnus alalunga, are widely distributed in tropical, sub-tropical and temperate zones between approximately 10–50uN and 5–45uS worldwide [1]
Histological analysis indicated that females,85 cm fork length (FL) were predominantly immature except for a small number of fish between 74 and 85 cm FL that were mature and classed as either spawning capable, spawning, regressing or regenerating (Fig. 5)
Analysis of sex ratios indicated that males dominate length classes above 95 cm FL

Summary

Introduction

Thunnus alalunga, are widely distributed in tropical, sub-tropical and temperate zones between approximately 10–50uN and 5–45uS worldwide [1]. Assessments of the status of albacore stocks currently range from overexploited in the North Atlantic Ocean through to moderately exploited in the South Pacific Ocean [6], [7], [8], [9], [10]. By age 1 year (,45–50 cm fork length; FL), juveniles move south and recruit to the New Zealand surface fisheries and the U.S troll fishery in the sub-tropical convergence zone (to approximately 130uW) [15]. These fisheries predominantly catch juveniles and sub-adults up to ,80–90 cm FL from December to April. Catch rates of albacore in the subtropics usually peak in December–January and May–July [19], consistent with an annual north-south migration of albacore

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