Insights on meagre (Argyrosomus regius) spatial ecology around the Gironde Estuary based on satellite telemetry

Meagre , Argyrosomus regius , one of Europe's largest coastal top predatory fish species, plays an important role in commercial and recreational fisheries. However, this species is particularly vulnerable due to overfishing, high genetic fragmentation, late first reproduction, and the restriction of spawning to limited, heavily impacted coastal areas. Understanding its spatial ecology and behaviour is therefore essential for effective fisheries management and conservation. We used pop-up satellite archival tags to investigate the horizontal movements, and depth-temperature preferences of meagre in one of their main spawning areas, the Gironde Estuary, France. A total of 37 fish were tagged, of which 28 provided useable data for primary geolocation analyses, with attachment durations ranging from 1 to 176 days (mean = 50 days). These data revealed a seasonal shift in both vertical and horizontal habitat use, mainly influenced by environmental temperature shifts, with fish utilizing shallow warmer waters during the summer and deeper cooler waters during the winter. The maximum depth observed was 141.5 m and water temperatures experienced ranged between 12.6 °C and 24.9 °C (mean = 19.1 ± 1.92 °C). Depth use was broader in winter than in summer, while temperature variation followed the opposite pattern, being wider in summer and narrower in winter. A novel approach was developed to incorporate Continuous Wavelet Transform (CWT)-derived thermal periodicity as auxiliary spatial evidence in geolocation models, using semidiurnal temperature oscillations to identify periods potentially associated with tidally influenced habitats in the Gironde Estuary. Reconstructed distributions predominantly supported estuary-associated, coastal and shelf habitat use, with more extensive coastal movements in some individuals and later use of deeper shelf habitats in the longest well-resolved record. These findings provide key insights into the habitat use and migration patterns of this economically important species and highlight the importance of protecting critical aggregation and spawning areas for effective spatial management.