english

The BoucleDor research project (2016-2020) was funded by the "European Regional Development Fund" (ERDF) and the French "Occitanie / Pyrénées-Méditerranée" region.

It aimed at gathering the missing ecological knowledge necessary to fully understand population structure and dynamics in a fish of high economical value in the Gulf of Lions (NW Mediterranean Sea) : the gilthead seabream (Sparus aurata L.). To do this, we combined for the first time the unique individual information that can be derived from the structural and chemical analysis of fish otolith ("ear stones") with advanced techniques in genetics and modeling.

Objectives

The project was structured around four main objectives (all corresponding to questions still unanswered regarding the species’ ecology in the Gulf of Lions) :

• Locating the local spawning areas of the species and identifying the main origin of the juveniles present in each lagoon nursery area,
• Unraveling relationships between genotype, habitat of life and growth for the early stages of life,
• describing lifetime trade-offs between somatic growth and reproduction at the population scale,
• Closing the loop by specifying the links between genotype, habitat of life and fitness for the individals that reach the adult stage.

Tools

For this, we combined the unique and valuable information derived from the structural and chemical analysis of fish otoliths (age, physiological history, successive habitats inhabited during fish life and corresponding specific growth rates) with biological data from the same individuals (genotype, size, weight, sexual status, fertility) and results from currents modelling in coastal zone in order to clarify, for the first time, the links between the genotype, the habitat(s) of life of S. aurata individuals and their likelihood to contribute to the next generation (or fitness).

This was applied to more than 400 individuals of the species (larvae and juveniles < 1 year, males of 1-2 years and females > 4 years) collected at sea and in four contrasting coastal lagoons spread along the littoral of the Gulf of Lions (Salses-Leucate, Bages-Sigean, Thau and Mauguio lagoons), over at least 2 consecutive years.

Expected results

This inovative approach allowed identification of S. aurata local spawning areas and key habitats, and completion of the description of its local life cycle by specifying the respective influences of genome and environment in the maintenance of its local meta-population.

It also allowed identifying the littoral habitats to preserve first if we are to maintain local exploited stocks. Finally, it allowed predicting the evolution of these stocks in the face of environmental change, by implementing the longitudinal lifetime growth data derived from otoliths analysis into emerging population dynamics models (IPMs) based on repeated individual size estimates.

This information was urgently needed to preserve the high value biological resource represented by the adult stock of this emblematic Mediterranean fish.

For more information, please contact : Dr. Audrey Darnaude (CNRS, UMR 9190 MARBEC)