Movement ecology determines isotopic niche width in the undulate skate Raja undulata

Functional connectivity patterns of threatened species provide critical information for effective management and conservation spatial planning. In this study, we used a non-lethal novel combination of acoustic telemetry and stable isotope analysis (SIA) on the Near Threatened elasmobranch Raja undulata to evaluate shifts in resource/space use in response to differences in residency patterns within a marine protected area (MPA) in NW Spain. By using acoustic telemetry, we classified individuals of a local population of R. undulata as high- or low-residence fish based on estimates of residence index (% of days present within the studied MPA). Individuals with a high residence index (>= 50%) showed a narrower isotopic niche width than low-residence fish, as they were exposed to a limited variety of habitats and food resources. Conversely, low-residence fish (mainly females) showed wider isotopic niche widths, indicative of greater diversity of resources from different environments. Therefore, we hypothesize that low-residence individuals play an important role connecting different habitats and even populations, particularly through dispersion patterns of females along the coast. This study provides valuable insights into the movement and resource ecology of R. undulata and their role in the functional connectivity of the coastal ecosystem, with direct applicability to inform management of the studied MPA.