Abstract
Albacore tuna (Thunnus alalunga) has a distinctly complex life history in which juveniles and adults separate geographically but at times inhabit the same spaces sequentially. The species also migrates long distances and presumably experiences varied regimes of physical stress over a lifetime. There are, therefore, many opportunities for population structure to arise based on stochastic differences or environmental factors that promote local adaptation. However, with the extent of mobility consistently demonstrated by tagged individuals, there is also a strong argument for panmixia within an ocean basin. It is important to confirm such assumptions from a population genetics standpoint for this species in particular because albacore is one of the principal market tuna species that sustains massive global fisheries and yet is also a slow‐growing temperate tuna. Consequently, we used 1,837 neutral SNP loci and 89 loci under potential selection to analyze population genetic structure among five sample groups collected from the western and central South Pacific. We found no evidence to challenge panmixia at neutral loci, but strong indications of structuring at adaptive loci. One population sample, from French Polynesia in 2004, was particularly differentiated. Unfortunately, the current study cannot infer whether the divergence is geographic or temporal, or possibly caused by sample distribution. We encourage future studies to include potentially adaptive loci and to continue fine‐scale observations within an ocean basin, and not to assume genome‐wide panmixia.
Highlights
Albacore tuna (Thunnus alalunga) (Figure 1) fills an unusual niche among economically important tuna species
There is no evidence of current overfishing of albacore tuna in any ocean basin (ISSF, 2017), but there is no comprehensive study that assesses all phases of the species' complex life history
Fish specimens were selected for analysis from tissue samples ar‐ chived in a tissue bank collection managed by the Pacific Community (SPC) under the auspices of the Western and Central Pacific Fisheries Commission (WCPFC), in Noumea, New Caledonia
Summary
Albacore tuna (Thunnus alalunga) (Figure 1) fills an unusual niche among economically important tuna species. Fish in the Indian and South Pacific Ocean spawn in the tropics during the spring and summer months and make their first migration to high latitudes largely undetected, appearing around 40°S roughly a year later (Farley, Williams, Hoyle, Davies, & Nicol, 2013). Juveniles persist at high latitudes until they reach sexual maturity and in the meantime follow smaller summer migrations to feeding grounds at latitudes of 15–25°S (Chen, Lee, & Tzeng, 2005) Once they become sexually mature, fish move closer to the equator, wintering in the same latitudes that become juvenile feeding grounds in the sum‐ mer, and migrating in the spring into tropical waters
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