Spawning-related fish movement synchrony of white seabream Diplodus sargus in a no-take zone

Studies assessing fish spatial behaviour are essential to better understand the performance of marine protected areas. However, few studies have focused on the fine-scale movements related to reproduction, a key feature in a population's perpetuation. Knowledge of movements modulated by reproduction is particularly important since migrations towards spawning grounds may increase the vulnerability to threats if these occur outside protected areas. Further, reproductive behavioural polymorphism is widely understudied but may affect reproductive success. In this work, we used acoustic telemetry to study a harvested fish, Diplodus sargus, within a small no-take zone in Portugal. To our knowledge, this is one of the first studies to focus on both the environmental and spatial features affecting D. sargus reproduction and the first to explore intraspecific variability of spawning movements. We report, during the spawning period, short-term (<1 d) and synchronised wider movements towards the open sea and deeper areas-'extraordinary movements'-involving 34% of the individuals. These extraordinary movements were associated with environmental factors known to trigger reproduction in this species (low but increasing photoperiod and temperature, waxing and full moon phases). Our results suggest that different behavioural groups (residents, commuters and low site-attached fish) exhibiting differences in spatial use may aggregate and spawn simultaneously, which may contribute to the maintenance of behavioural polymorphisms and the species' evolutionary adaptability. These findings have implications for the conservation of D. sargus and are relevant to other species that also conduct such critical migrations. Our results should enable adaptive management of fisheries targeting this species.