ZIMARROI

Context

In highly migratory species such as Atlantic bluefin tuna, climate-change-driven shifts in spatio-temporal distribution can affect the viability of Basque fisheries in the Bay of Biscay, as well as the availability of the resource. These spatial changes may also influence the criteria used to allocate Total Allowable Catches (TACs) and quotas among countries.

In this context, the concept of zonal attachment is being considered as a potential criterion for quota allocation in regional fisheries management organisations such as ICCAT and IOTC. Several North Atlantic countries with small bluefin tuna quotas have promoted electronic tagging studies to demonstrate the species’ recurrent use of their waters, as an argument in possible future revisions of quota allocation.

Against this backdrop, it is necessary to improve knowledge of the spatio-temporal distribution of bluefin tuna and its fidelity to the Bay of Biscay, in order to provide robust scientific evidence that supports stronger, more adaptive management of the resource at both local and international scales.

Objectives

The overall objective of the project is to determine the role of the Bay of Biscay in the bluefin tuna life cycle—across age groups and throughout all seasons—using a multidisciplinary approach.

Specific objectives are to:

• Improve understanding of the spatio-temporal distribution of bluefin tuna in the Bay of Biscay using advanced technologies, including electronic tagging, genetic analyses, chemical analyses of otoliths, and larval surveys in Cantabrian Sea waters.
• Determine whether the Bay of Biscay remains the main Atlantic feeding ground for bluefin tuna, and quantify its relative importance compared to other feeding areas.
• Assess the degree of fidelity of bluefin tuna to the Bay of Biscay, both within years and across successive interannual migrations.
• Analyse potential changes in the distribution of preferred habitat over recent decades and their impact on interactions with different fishing gears.
• Clarify the population origin of bluefin tuna present in the Bay of Biscay, determining whether it comes predominantly from the Mediterranean or also includes individuals from the Gulf of Mexico.
• Evaluate the possible role of the Bay of Biscay as a new spawning area for bluefin tuna.

Expected impact

Detailed knowledge of the spatio-temporal distribution of highly migratory species such as bluefin tuna is essential for effective, adaptive fisheries management—both for target fisheries and for associated fisheries, such as small pelagic fisheries.

In the current context, where several countries with little or no bluefin tuna quota are generating scientific evidence of the species’ presence in their waters, this project’s results will provide strategic information that may be relevant in future quota allocation debates.

In addition, tracking the population origin of bluefin tuna present in the Bay of Biscay will help verify that the current management framework remains appropriate and that no exceptional circumstances arise that could compromise the application of the TAC. Finally, improved understanding of the seasonal availability of the resource will support the correct definition or adjustment of fishing and ranching periods, contributing to more efficient and sustainable management.

Funding