MUGITUN

Context

Climate change is altering marine habitat conditions, driving shifts in the distribution of many fish species in response to changes in water temperature and prey availability. The Atlantic bluefin tuna (ABFT), despite its broad thermal tolerance, shows distribution patterns and migratory behavior that are closely linked to food availability.

Significant uncertainties remain regarding the population structure of Atlantic bluefin tuna, particularly concerning the mixing of eastern and western stocks in the Atlantic and the potential coexistence of resident and migratory components in the Mediterranean. While electronic tagging studies provide detailed information at the individual level, their limited coverage constrains population-level inferences.

This project addresses these uncertainties through otolith microchemistry. Oxygen isotope analysis (δ¹⁸O), previously validated as a natural thermometer for bluefin tuna, enables reconstruction of individuals’ thermal histories and assessment of different migratory strategies. Complementary carbon isotope analysis (δ¹³C) provides insights into metabolic rates and the species’ thermal constraints, delivering a robust scientific basis for management and conservation.

Objectives

The overall objective of the project is to enhance knowledge of the migratory patterns and thermal constraints of Atlantic bluefin tuna as a foundation for sustainable species management.

Specifically, the project aims to:

• Determine whether Atlantic bluefin tuna exhibit different migratory strategies, such as highly migratory or resident behaviors.
• Identify the predominant migratory strategy among the individuals studied.
• Define the optimal temperature range for Mediterranean bluefin tuna through δ¹⁸O and δ¹³C isotopic analysis.
• Assess whether the Mediterranean population has experienced changes in environmental temperature and metabolic rate over the past two decades.

Results

By analyzing δ¹⁸O and δ¹³C values in the calcium carbonate composing the otoliths, it has been possible to distinguish tuna that have inhabited the western Atlantic from those that have remained in the eastern Atlantic and the Mediterranean.

To date, the number of individuals analyzed has been limited, and evidence of both migratory strategies has been confirmed. The next step will be to analyze a larger sample size to determine which strategy is most prevalent and in what proportions each occurs.

Expected Impact

The knowledge generated will contribute to the design of fisheries management measures better aligned with the true population structure, supporting long-term management and conservation strategies aimed at the sustainable exploitation of Atlantic bluefin tuna.

Funding