Plenary Speaker: Climate variability, estuarine hydrodynamics and fish reproduction in the Plata estuary.

ACHA E.M.

Mar del Plata

Conferencia; Coastal and Estuarine Research Federation Conference (CERF 2012), The changing coastal and estuarine environment: A comparative approach; 2012

Coastal and Estuarine Research Federation Conference

The most common life-history cycle of estuarine fishes involves spawning of planktonic eggs in marine waters, and then recruitment in estuaries as larvae or juveniles; only a few species breed within estuaries. Due to the net estuarine waters seawards movement, it has been hypothesized that exportation of early life-history stages from estuaries towards the sea represent a major problem for estuarine spawners. Unlike most estuaries, spawning activity is rather common in the Río de la Plata, in which the existence of retention mechanisms has been shown. We present the reproduction of the whitemouth croaker (Micropogonias furnieri) as case study. The species is the main target of the coastal fisheries of Argentina and Uruguay. Croaker?s age structure shows the predominance of certain year classes, which are indicative of recruitment fluctuations. Spawning occur well inside the estuary at the bottom salinity front, which is where their larvae remain retained. In this manner, the reproductive success of croakers appears to be linked to the dynamics of the estuarine waters. The estuary is under the effects of large river discharge variations associated to the ENSO and other climatic signals. The effects of extreme river discharges on retention may regulate croaker recruitment by promoting low recruitment during high discharge periods, and vice versa. The climatology of the water excesses and shortages during the 20th century in the basin revealed that almost all of the excess critical periods occurred after 1950. Regarding future scenarios, the extent to which alterations that are associated with global climate change can impact the retention properties of the estuary and the resulting consequences for its populations are unclear, and these issues cannot be addressed without a high degree of speculation; however a continual increasing of positive anomalies could intensify the declining trend of the stock size that is produced by fishing pressure.