Absolute abundance of southern bluefin tuna estimated by close-kin mark-recapture.

Mark V Bravington,Campbell R Davies,Peter M Grewe

doi:10.1038/ncomms13162

Mark V Bravington, Campbell R Davies + Show 1 more

Open Access

https://doi.org/10.1038/ncomms13162

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Abstract

Southern bluefin tuna is a highly valuable, severely depleted species, whose abundance and productivity have been difficult to assess with conventional fishery data. Here we use large-scale genotyping to look for parent–offspring pairs among 14,000 tissue samples of juvenile and adult tuna collected from the fisheries, finding 45 pairs in total. Using a modified mark-recapture framework where ‘recaptures' are kin rather than individuals, we can estimate adult abundance and other demographic parameters such as survival, without needing to use contentious fishery catch or effort data. Our abundance estimates are substantially higher and more precise than previously thought, indicating a somewhat less-depleted and more productive stock. More broadly, this technique of ‘close-kin mark-recapture' has widespread utility in fisheries and wildlife conservation. It estimates a key parameter for management—the absolute abundance of adults—while avoiding the expense of independent surveys or tag-release programmes, and the interpretational problems of fishery catch rates.

Highlights

Southern bluefin tuna is a highly valuable, severely depleted species, whose abundance and productivity have been difficult to assess with conventional fishery data
We present a successful application to southern bluefin tuna (SBT; Thunnus maccoyii), a highly migratory, heavily depleted species that supports a valuable international fishery (4$1bn p.a.), yet where traditional but highly contentious data sources have left great uncertainty about its status and recovery prospects
Close-kin mark-recapture (CKMR) offers a breakthrough for many commercial fisheries, and other ecological applications without a cost-effective monitoring tool because of compelling advantages over more traditional data sources: low cost, logistic simplicity, few assumptions and lack of susceptibility to reporting biases

Summary

Introduction

Southern bluefin tuna is a highly valuable, severely depleted species, whose abundance and productivity have been difficult to assess with conventional fishery data. Our abundance estimates are substantially higher and more precise than previously thought, indicating a somewhat less-depleted and more productive stock This technique of ‘close-kin mark-recapture’ has widespread utility in fisheries and wildlife conservation. It estimates a key parameter for management— the absolute abundance of adults—while avoiding the expense of independent surveys or tag-release programmes, and the interpretational problems of fishery catch rates. CKMR bypasses the dependence on problematic fishery-derived data, while avoiding the expense of fishery-independent studies such as dedicated surveys or tagging programmes It promises to revolutionize the monitoring of previously intractable species in marine, freshwater and terrestrial environments. This condition can be relaxed in real applications, as described below

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