Insights into the spatio-temporal variability of spawning in a territorial coastal fish by combining observations, modelling and literature review

In bipartite life cycle fishes, spawning represents the onset of propagules dispersal, with eggs and larvae experiencing anisotropic transport and high mortality rates, before eventually metamorphosing and settling. Hence, early-life stages operate as bottlenecks for population demography by strongly constraining recruitment. Despite its significance, spawning is rarely explicitly considered in ecosystem management due to a lack of knowledge, for many species, about where and when spawning occurs. Previous evidences suggest that temperature is among the main drivers of spawning in Teleosts. Using the ecologically and economically relevant white seabream Diplodus sargus in the central Mediterranean Sea as a case study, we assess the abiotic factors that regulate the onset and duration of spawning and subsequent dispersal. Lagrangian backtracking simulations fed with early-life observations allow locating 11 spawning events, which are then associated to simulated temperatures ranging from 14.8° C to 20.6° C, in close agreement with previous estimates. Based on this range of suitable temperatures, we model the spatio-temporal variability of spawning success at broad-scale over 10 years (2005–2014) following the backtracking approach with hypothetical constant settlement areas. It highlights a prominent inter-annual variability in the Adriatic and Siculo-Tunisian strait driven by oceanographic processes. Moreover, a powerful clustering method uncovers relatively stable spawning areas in the Ligurian and Tyrrhenian seas with both early (January to Mid-February) and late (April to June) spawning peaks. Our methodology can be applied to other species and oceanic systems to investigate how oceanic processes impact spawning success, enabling the design of sound management strategies.