Assessing the effects of climate change and fishing management on demersal stocks in the western Mediterranean: Rethinking WestMed-MAP effort reductions in the Balearic Islands

Francesc Ordines, Paula Sánchez-Zulueta, Maria Valls, Olga P. Malagón, Marco Scotti, Marc Farré, Gabriel Jordà, Julia Jaca, M. Teresa Farriols, Antoni Quetglas, Enric Massutí, Beatriz Guijarro, 2026. Assessing the effects of climate change and fishing management on demersal stocks in the western Mediterranean: Rethinking WestMed-MAP effort reductions in the Balearic Islands. Marine Policy.January 2027.107285.Volume 195. https://doi.org/10.1016/j.marpol.2026.107285

Abstract:Bottom trawl fishing effort in the Balearic Islands has decreased considerably in recent decades due to a progressive fleet reduction and the implementation, since 2020, of the effort regime under the multiannual plan for demersal fisheries in the western Mediterranean (WestMed-MAP). By 2024, this regime had reduced the average annual fishing days by 40% compared to the 2015–2017 baseline period. Concurrently, seawater temperature is increasing. We used the Ecosim model to explore the long-term effects of several WestMed-MAP and climate change scenarios on key demersal resources and vulnerable fish species in the Balearic Islands. Management effects were stock-dependent. Some stocks (deep-water rose shrimp, mullets and rays) reached biomass and catch levels comparable to those expected at maximum sustainable yield (MSY) under fishing effort levels prior to the WestMed-MAP, or following its early (2022) implementation. Conversely, hake and red shrimp would not recover to MSY biomass levels, even under 2024 effort reductions coupled with selectivity improvements. Deep-water rose shrimp was the only species positively affected by global warming, whereas Norway lobster was negatively impacted by warming, only recovers under a no fishing scenario. All successful scenarios required over 5 years to achieve full potential recovery. These results call for a re-evaluation of WestMed-MAP fishing effort reductions implemented in the Balearic Islands, highlighting the need for a regional downscaling that considers specific fishing strategies and the initial state of local stocks, as well as the time lag required to detect expected management effects.

Keywords:stock recovery,fishing effort regime,global warming,ecopath with ecosim.