Long-term variability of Norway lobster (Nephrops norvegicus) landings in relation to a changing climate in the Northwestern Mediterranean Sea

Abstract. Understanding how environmental variability shapes the dynamics of demersal resources is essential for sustainable fisheries management in climate‑sensitive regions such as the Northwestern Mediterranean Sea. This study analyses more than five decades (1970–2024) of Norway lobster (Nephrops norvegicus) landings in FAO GSA 6 to identify the drivers underlying its decadal variability and the sharp decline observed since the mid‑2010s. Fishery‑dependent data (landings, Landings Per Unit of Effort (LPUE), depth distribution, and fishing effort) was combined with oceanographic descriptors. Empirical Orthogonal Functions (EOFs) were applied to temperature, salinity, along‑shore and across-shore currents at surface, 200 m, 400 m, and 600 m to extract dominant modes of oceanographic variability and assess their correlation with fisheries indicators. The most relevant physical signal was a widespread warming and salinization of intermediate waters, captured within its EOF first modes, that showed the strongest negative correlation with landings and LPUE. Positive phases of these modes corresponded to positive thermal and salinity anomalies and coincided with declining LPUE, a slight deepening of its centroid (depth of maximum LPUE), and reduced landings. These results indicate that intermediate‑water warming and salinization might be a key mechanism constraining the Norway lobster catchability. Circulation changes also seemed to influence LPUEs. The second EOF mode of along‑shore velocity at 200 m captured variability in the Liguro‑Provençal‑Catalan current and the North Balearic Front. Its positive phases, reflecting a strengthened boundary current and enhanced recirculation north of the Balearic Islands, were positively correlated with landings, suggesting that frontal dynamics may modulate habitat suitability, for example. Overall, the recent decline of the Norway lobster landings cannot be attributed to fishing effort alone but is also linked to climate‑driven changes in intermediate‑water physical characteristics. These findings highlight the need to integrate oceanographic indicators into stock assessments to anticipate further climate‑induced shifts in demersal resources.