A team from the Centro Oceanográfico de Baleares of the Spanish Institute of Oceanography (IEO-CSIC) demonstrated that the protection of seabeds from trawling enhances the diet quality of species inhabiting those areas.
The work, published in the journal ICES Journal of Marine Science, analyzed the ecological effects of the trawling ban in the Site of Community Importance (SCI) of the Menorca Channel. The area was included in the Natura 2000 Network and partially declared a Fisheries Protection Zone (FPZ) in 2016.
More complex habitats and higher quality prey
“Species living near the seabed not only benefit from a more complex habitat, but also access prey with higher energy quality,” explained IEO-CSIC researcher and lead author of the study, María Valls.
The study was conducted in the spring of 2022 and 2023 aboard the vessels Ángeles Alvariño and Ramón Margalef. The research combined techniques of stomach content analysis and the composition of stable carbon and nitrogen isotopes in the muscle of five commercial species:
- Red mullet (Mullus surmuletus)
- Comber (Serranus cabrilla)
- Streaked gurnard (Chelidonichthys lastoviza)
- Black scorpionfish (Scorpaena notata)
- Common octopus (Octopus vulgaris)
Additionally, the energy content of their prey was determined through calorimetry.
Comparison between areas with different fishing pressure
The analyses were conducted in three areas with different levels of exploitation:
- The FPZ of the Menorca Channel, closed to trawling.
- An area within the SCI still open to fishing.
- An area adjacent to the SCI on the east coast of Mallorca.
The results showed that, in the protected area, species like the red mullet and the comber consume prey richer in energy —fish, polychaetes, and shrimp—, resulting in a higher caloric intake and a better quality diet.
In contrast, more opportunistic species like the octopus or the streaked gurnard showed more variable responses. This is likely due to more flexible feeding habits or a preference for prey less sensitive to the impact of trawling.
Ecological and fishing benefits
“The improvement in food quality and the recovery of the benthos after the trawling ban have a direct effect on the physiology and productivity of commercial species,” highlighted study co-author Francesc Ordines.
The researchers concluded that protected areas are an effective tool not only for conserving habitats but also for maintaining healthier and more productive ecosystems and fisheries.
Marfish Project and European funding
The study was developed within the framework of the Marfish project, which seeks to evaluate the response of fishery resources to protection in a multidisciplinary manner. It was funded by the Conselleria de Fondos Europeos, Universidad y Cultura.
The campaigns were integrated into the SosMed (Improvement of knowledge for the sustainability of demersal fisheries in the western Mediterranean) project, funded with European Next Generation funds from the Recovery, Transformation, and Resilience Plan, through an agreement between the Ministry of Agriculture, Fisheries and Food and the IEO-CSIC.
Measurable benefits in a short time
The research reinforces the evidence that seabed protection generates measurable ecological benefits in a relatively short period following the trawling ban. It not only favors the recovery of the habitat but also modifies the trophic relationships among demersal species, improving what and how bottom fish feed.
The Menorca Channel thus becomes an example of how responsible fishery management can balance conservation and productivity, ensuring a more sustainable future for marine ecosystems and the communities that depend on them.
