Abstract

The southern hake, Merluccius australis, is one of the most important marine fishery resources in Chilean Patagonia. However, little is known about its early life history, especially the transport of eggs and larvae and the connectivity between spawning and nursery areas. An individual-based model (IBM) of the early life stages of M. australis, coupled to a hydrodynamic model, was used to track virtual individuals released from known spawning locations and identify potential nursery areas. The simulations were used to assess connectivity and retention of M. australis eggs and yolk-sac larvae within (and between) the continental shelf (offshore) and the inner sea (inshore) zones. The inshore zone included two spawning and nursery areas (Inner Sea of Chiloe (ISCh), Inner Sea of Moraleda Channel ISM)) and the offshore zone included three spawning and nursery areas (Guafo Island, Guamblin Island, and the Taitao Peninsula). The hydrodynamic model was validated using available observations (oceanographic surveys and the World Ocean Atlas 2018) for winter and spring, periods during which M. australis reproductive activity peaks. The IBM reproduced well the observed seasonal variability of egg and larval distributions. Individuals from the offshore spawning areas had low connectivity with those in the inshore nursery areas in winter and spring. However, individuals from the inshore spawning areas showed a high degree of connectivity with one of the offshore nursery areas (Guafo) during winter and spring, but low connectivity between the inshore ones (ISCh and ISM). Guamblin (in winter) and ISCh (in spring) were the most important retention areas. A conceptual model is proposed to represent the connectivity in early developmental stages between the spawning and nursery areas of M. australis: ichthyoplankton is transported from inshore to offshore in winter when little spawning occurs inshore, but not in spring when spawning and retention increases inshore. Retention in the offshore zone in winter is significant, with almost no connectivity with the inshore zone. Since the main spawning of the species occurs in winter in the offshore zone and secondarily in the inshore zone in spring, the seasonal differences in dispersal patterns seem to be part of the reproductive strategy of the species, which apparently confers advantages for the offspring by promoting development in the most advantageous feeding environment for each season (offshore in winter and inshore in spring).