Wrasses Equipped with Mobile Technology to Analyze the State of Their Populations

Every September 1st, thousands of fishermen head out to sea on the first permitted day for catching wrasse, a small fish that inhabits sandy seabeds.

During this period, the first wrasses caught reach the markets at prices up to 100 euros per kilogram. This species is highly valued by the island's fishermen due to its significant social, economic, and cultural importance. However, there are many uncertainties about its life cycle, raising doubts about the future sustainability of its populations and this socio-economic activity on the islands.

With the warming of the waters, the spread of invasive species, coastal overcrowding, the spread of diseases, and pollution, it is unknown how wild wrasse populations will react. Although temporary fishing bans and marine reserves have helped stabilize wrasse populations, the impact of these new challenges on their future remains unclear.

To investigate how this species grows and reproduces, as well as to determine natural causes of mortality such as diseases, aging, and predation, the Mediterranean Institute for Advanced Studies, IMEDEA (CSIC-UIB), the University of the Balearic Islands (UIB), the Institute for Agri-Food and Fisheries Research and Training of the Balearic Islands GOIB (IRFAP), and the Institute of Marine Research of Vigo (IIM), are conducting a pioneering experiment. This summer, a hundred wrasses from the waters of Mallorca have been tagged with a small radiocommunication device.

These small electronic devices, harmless to the fish, emit a low-frequency radio signal that allows researchers to determine their location and health status using acoustic telemetry techniques and a network of underwater antennas installed on the seabed, explains Dr. Josep Alós, the principal investigator of the project. Half of the wrasses were tagged in fully protected areas of the marine reserves of Migjorn, Llevant, and the Bay of Palma to study mortality due to diseases and predation, without fishing interference. The rest were tagged in popular fishing spots such as Cala Mesquida, Caló des Màrmols, and Rafalbeig, to determine how many are caught by fishermen.

In addition to the electronically tracked individuals, around 500 wrasses have been externally marked with yellow tags and an identification code. This makes these fish visible if caught, and fishermen in the Balearic Islands are asked to report recaptures to IMEDEA, emphasizes Dr. Alós.

With the data obtained from the wrasses equipped with electronic devices and those marked with external tags, researchers will be able to quantify their growth, reproduction, and mortality, a key aspect for understanding population dynamics, states Dr. Alós. This will generate knowledge to ensure stable wrasse populations and secure the future of this highly valued activity for the citizens of the Balearic Islands, concludes Dr. Alós. The results will be presented at the First Raor Study Day, which will be held at Club Nàutic S’Arenal on August 24, just a week before the opening of the 2024 wrasse fishing season.