A pioneering study in the Balearic Islands reveals that connected marine reserves better protect fish.

PalmA study by the Mediterranean Institute for Advanced Studies (IMEDEA) (CSIC-UIB), which monitored fish using acoustic telemetry for two years, has shown that marine reserves function better when they are connected to each other. The results highlight the importance of the Balearic Islands' marine reserves in protecting and connecting fish populations, the institution reported in a statement about the project. Coremar, which has studied the movements and behavior of key species for biodiversity and fisheries, such as grouper, dentu, amberjack, spectacle, and shortfin grouper.

The recently completed study used acoustic telemetry, a technology that allows fish movements to be tracked. To do this, the fish are captured and undergo a small surgery in which they are implanted with an electronic device the size of a wineglass. This device emits unique acoustic signals that are detected by receivers installed on the seabed. Each time a tagged fish passes near a receiver, its presence is recorded along with environmental variables, such as temperature. This technique allows us to reconstruct the movements and activity of individuals and also to understand how they use marine reserves and how they respond to changes in environmental factors.

The project has consolidated a pioneering marine monitoring network with 38 receivers distributed between Mallorca and Menorca (Balearic Tracking Network, BTN), integrated into another European network (European Tracking Network), which positions the Balearic Islands as a strategic international hub. During the project, 126 fish of different species were tagged, detected more than two million times by BTN receivers. In addition, the devices installed at sea recorded four million data points of seabed temperature.

Environmental conditions

The results provide a better understanding of fish activity based on environmental conditions, information that is especially relevant in the face of climate change. The implanted transmitters have long-lasting batteries, lasting between 5 and 10 years, ensuring that many of these individuals will continue to provide data in the coming years. "We know more about how fish use and connect different reserves, when they are most active, and which areas are critical for their conservation," explains Eneko Aspillaga, the project's principal investigator.

The results highlight the importance of marine reserves as an interconnected system that not only protects fish within their boundaries but also facilitates their movement between different areas. This knowledge has made it possible to "calculate detailed distribution areas for each species, identify priority areas for management, and reinforce the idea that reserves function best when they are connected to each other."

The project has also marked the start of telemetry studies in Menorca, with the installation of the first receivers in the Aire Island Marine Reserve, in collaboration with the Jaume Ferrer Station (COB-IEO, CSIC). This young reserve, designated in 2019, has been ideal for studying the early stages of grouper population settlement, providing key information on residence and dispersal patterns.

Among the most surprising findings are recaptures that show large-scale fish movements. The most striking case is that of a juvenile grouper tagged on Aire Island and captured months later on the Catalan coast. A cod was also documented (Mycteroperca rubra) tagged in Menorca and later caught in Portocristo. "These results have surprised us and raise new scientific questions. Although anecdotal, they are the first indications that the Balearic marine reserves are not only essential at the island level, but also play a crucial ecological role for the entire northwestern Mediterranean," Aspillaga emphasizes.

The importance of the project Coremar Its results can improve the management of marine resources and, in addition, it has consolidated a permanent monitoring infrastructure that is unique in the Balearic Islands and an international benchmark in marine research and conservation.