Where do recruits come from? Backward Lagrangian simulation for the deep water rose shrimps in the Central Mediterranean Sea

Backward-in-time Lagrangian dispersion models can efficiently reconstruct drifters trajectories by linking known arrival positions to potential sources. This approach was applied to the deep water rose shrimp (Parapenaeus longirostris) in the Strait of Sicily (central Mediterranean Sea). The objective was to identify the potential spawning areas of the larvae that settle in the known nursery grounds of the northern sector of the Strait of Sicily, thus quantifying the extent of the potential contribution to recruitment from the surrounding regions. Numerical simulations were performed over 11 years (2005-2015) and for two different periods (spring/summer and autumn/winter) corresponding to the species' spawning peaks in the region. The persistence over time of potential spawning areas was identified through a Hotspot analysis of the backward trajectories end-points, filtered to meet a suitable depth range for spawners. The results confirmed the expected downstream connectivity between spawning and nursery grounds along the Sicilian-Maltese shelf and, notably, indicated that these spawning grounds contribute to the high productivity and resilience of deep water rose shrimp fisheries in the northern Strait of Sicily more than the spawning grounds in surrounding regions. A minor and time-varying contribution is due to potential spawning areas identified on the African shelf. These results are important to adequately define the geographical scale for the assessment and management of this important fishery resource in the Strait of Sicily. In particular, the assumption of a single stock that does not consider the spatial structure of the population should be revised for the purpose of fisheries management.