Bluefin tuna was overfished between 1990 and 2008, which prompted institutions to react to a scenario that threatened the future of the species. Thus, the International Commission for the Conservation of Atlantic Tunas (ICCAT) implemented a recovery plan in 2008 that achieved and continues to achieve very favourable results.

Efforts to sustainably manage bluefin tuna, however, have not ceased. An example of this is the BFT Index project, an initiative promoted by the Vice-Ministry of Agriculture, Fisheries and Food Policy of the Basque Government.


The general objective of the project is to monitor the biomass trends of bluefin tuna in the Bay of Biscay, in order to have a fishery-independent index of abundance. This index can be used for stock assessment, progressively completing and replacing the current abundance index based on catch-per-unit-effort data. Specifically, the method chosen to estimate the biomass of bluefin tuna (mainly juveniles) is active acoustic prospecting, together with release fishing for confirmation of species identification and size sampling. The variables to be measured are the number of bluefin tuna schools, their relative size and the size class of the individuals. If the recordings allow, the dimensions will also be measured and the biomass of the schools will be estimated. If present, the focus will be more particularly on age class 1 (“matralla”), the abundance of which directly reflects the recruitment of the stock.

In doing so, this project aims to represent a first step towards a new approach to the management of bluefin tuna fisheries by incorporating a new tool and fishery-independent information that can help decision-making.

Expected results

The acoustic, morphological and geostatistical analysis of the aggregations observed during the transects will provide a first index, independent of fishing activity, of the abundance and distribution of juvenile bluefin tuna in the area.

In the medium term, we will be able to have a tool independent of the fishery to estimate the variations in the biomass of bluefin tuna in the Bay of Biscay, and use it for the assessment of the resource carried out by ICCAT.

Useful documentation

Protocol guide


Annual since 2015


Basque Government through the European Maritime and Fisheries Fund (EMFF)

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