The Mediterranean Sea, a vital marine resource, has experienced a significant decline in fish populations over the last few decades.

Multiple factors contribute to this decline, with a crucial question at the forefront: how are the fish faring beneath the surface?

Twenty years of scientific trawling by Ifremer researchers reveal trends in fish population dynamics.

The MEDITS campaign has been conducting annual trawls that mimic the practices of commercial fishermen since 1994, allowing for the collection and analysis of fish samples without the intention of sale or consumption.

The fish captured are systematically classified, weighed, and studied, providing valuable data on species abundance and demographic structure.

Grégoire Certain, head scientist of the MEDITS campaign, emphasizes that these scientific trawls enable the monitoring of around 200 different species, contributing to estimates of fish abundance in relation to the area fished.

This approach has sparked debate within the fishing community, albeit it has proven scientifically effective in estimating fish populations and understanding their reproductive structures.

As the research team prepares for their missions, logistics play a crucial role.

Angélique Jadaud, who oversees these at-sea campaigns, coordinates equipment and data collection efforts onboard the catamaran Europe.

The vessel serves as both a research platform and fishing boat, equipped for the meticulous evaluation of fish caught, which includes weighing, counting, and taking biological samples for contaminant analysis and genetic studies.

The Europe is set to execute trawls in areas such as the Gulf of Lion and the eastern coast of Corsica, where the fishing activity largely concerns a fleet of around fifty French trawlers.

The adherence to the MEDITS protocol is imperative for ensuring uniformity in data collection across the northern Mediterranean, which feeds into European databases that inform fisheries management policies, including species quotas and fishing regulations.

Data gathered from these campaigns suggest concerning trends across the Mediterranean.

Out of 16 fish populations surveyed, 12 are classified as overfished.

Notably, while the red mullet population has recovered, the hake stock remains critically depleted, especially in Franco-Spanish waters, with a significant portion of captured fish not reaching maturity before being caught.

Many juvenile fish, which do not meet commercial size, are discarded dead, leading to unnecessary losses for fisheries.

The sardine population also faces challenges, with average sizes and weights diminishing over two decades.

Research suggests changes in zooplankton communities may be to blame for this trend, leading to less efficient foraging and consequent reproductive issues among sardines.

The impacts of climate change on zooplankton sizes could be significant, as observed increases in deep water temperatures by 1°C since the 2000s further support shifts in marine ecosystems and fish distribution patterns.

Furthermore, species such as pink shrimp and calamari have also shown notable increases in abundance, altering the species composition in the Mediterranean.

However, as marine variations continue, the long-term implications of these ecosystem shifts remain uncertain for both fish populations and the fishing industry.

As the European Union deliberates potential adjustments to fishing regulations in response to these findings, it confronts challenges balancing the sustainability of fish stocks while accommodating the fishing community's needs.

The ongoing research efforts at Ifremer seek to clarify these dynamics, further enriching the understanding of Mediterranean marine life.