Abstract

Merluccius australis, known as southern hake, is a demersal fish that inhabit the southern tip of South America. The main spawning area is located in the outer sea of the Chilean Patagonia, where they aggregate to reproduce during the austral winter. An alternative spawning ground has been suggested within the inner sea where eggs of a few days old have been found. The relative importance of this spawning zone as well as the main environmental features that makes this inner zone suitable for spawning has not been assessed. We analyzed ichthyoplankton samples along with hydrographic data from oceanographic cruises (2003-2015) carried out in winter and spring to characterize both spawning zones. The observations were combined with a biophysical model that couples a hydrodynamic model (Regional Ocean Model System, ROMS) with an individual-based model (IBM, Ichthyop) to assess the connectivity of early life stages in the Chilean Patagonia. Field data show that the mean abundance of southern hake eggs in the outer sea exceeds 30 times the inner sea in winter, and four times the mean abundance during spring in the inner sea. Accordingly, the main spawning of the species occurs in winter in the outer sea and in spring in the inner sea. Preliminary results from biophysical model simulations show transport from the inner to the outer sea in winter but an increased retention in spring. At the outer sea occurred a significant retention in winter which decreased in spring. The seasons at which spawning occurs at both areas is associated with local oceanographic processes that enhance retention at the nursery areas. The development of different spatial spawning seasons at different zones is apparently linked to the inter-annual variability in environmental conditions at the main spawning zone offshore, by which the secondary spawning in the inner sea could be part of a reproductive strategy to ensure offspring survival when conditions in the outer sea are not favorable.