The study of spatial ecology in fish is crucial for the proper design of a marine protected area. A species is efficiently protected only if its regular movements are encompassed within the protected zone boundaries. Knowing space utilization behaviour is therefore fundamental, particularly for highly commercial species that are vulnerable to fisheries outside no-take zones (NTZ). This work presents a study of an ecologically and commercially important species, Diplodus sargus, within a small NTZ in Portugal, through acoustic telemetry. High residency and small home ranges were found for most fish, supporting previous research. However, the results also revealed the importance of a NTZ location. Indeed, a group of fish showed a home range located at the borders, partially outside the protected area, making them more vulnerable to fisheries. Although several studies have been published on D. sargus reproduction, its spatial behaviour in this specific area and during the breeding season is unknown. The present study report wider movements and towards deeper areas for most of the resident individuals during this key-period. Short (< a day) deep excursions (extraordinary vertical movements) were related to spawning events. To a lesser extent, they were also associated to a sheltering behaviour during rough sea.
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