Distribution and behavior of Argentine hake larvae: Evidences of a biophysical mechanism for self-recruitment at the North Patagonian shelf waters.

ALVAREZ COLOMBO G.; DATO C.; MACCHI, G.J.; PALMA E.; MACHINANDIARENA L.; CHRISTIANSEN H.E.; BETTI P.; MARTOS P.; CASTRO MACHADO F.; BROWN D.; EHRLICH M.D.; MIANZAN H. W.; ACHA E.M.

CIENCIAS MARINAS

INST INVESTIGACIONES OCEANOLOGICAS, U A B C, APARTADO POSTAL 423

Año: 2011 vol. 37 p. 633 - 657

0185-3880

It has been proposed that vertical movements of planktonic organisms coupled to a vertically stratified circulation pattern could determine a retention mechanism. The Patagonian stock of the Argentine hake Merluccius hubbsi, Marini 1933) spawns mainly during January–February in relation to a highly productive tidal frontal system. Even though a retention of fish eggs and larvae has been previously hypothesized at this system, it has not yet fully proven neither its mechanisms have been proposed for hake early stages. In order to improve the understanding of the physical and biological processes involved in larval hake survival and distribution, we focused on transport features and associated larval behavior that would allow for retention to the spawning area and further distribution of larvae to settlement grounds. To test this hypothesis at appropriate spatial and temporal scales we employed acoustic records to describe vertical and horizontal distribution patterns of hake larvae; discrete plankton samples in order to confirm acoustic targets identity; and outputs from a numerical circulation model to estimate currents patterns in the region during the hake spawning months. In coincidence with the development of a functional swimbladder, hake larvae of 4 mm and larger showed a strong correlation pattern of vertical distribution with a migrating sound scattering layer between the thermocline during the night and near-bottom depths during the day. This diel vertical migration pattern was associated to the structure of the circulation, equivalent to a two-layer flow, indicating a re-circulation pattern in the vertical plane. A resulting retention of early larval stages at the spawning area was evident from the acoustic data indicating the persistence of the bulk of hake larvae in the horizontal distributions during summer months, extending to the rest of the nursery grounds with the progress of the reproductive season in agreement with the general pattern of middle shelf bottom velocities produced by the numerical model. The results were discussed in the framework of the Bakun’s fundamental triad, identifying its elements. In addition, a conceptual model about the main biophysical coupling processes during the early life history of hake was proposed in order to gain insight about recruitment of this species.