Distribution of Micropoeonias furnieri at different maturity stages along an estuarine gradient and in relation to environmental factors

Whitemouth croaker (Micropogonias furnieri) maturity stages distribution and its relation to environmental factors was evaluated from 166 stations sampled within the Rio de la Plata estuary (36 degrees S-56 degrees W) during spring 1994-1999 and 2003. A canonical correspondence analysis was used to explain whitemouth croaker distribution and estimate its relation to environmental factors (depth, surface and bottom waters temperature, and salinity, bottom salinity and temperature horizontal gradients and vertical stratification). Results indicate that bottom salinity horizontal gradient (BSHG) and depth have a major influence on M. furnieri maturity stages spatial distribution; bottom salinity and temperature play a significant although secondary role. Spent and resting adult stages were associated to low BSHG, high salinity and low temperature while immature, gravid (with hydrated oocytes) and running stages to low salinity and high temperature. Although immature, gravid and running stages were clearly linked to similar bottom salinity they were segregated, with gravid and running stages associated to a strong BSHG. The distinct preferences of the different spawning stages result in a segregated distribution pattern along the main axis of the Rio ale la Plata estuary. The area with low salinity and high horizontal bottom salinity gradient (habitat for gravid and running stages) was located at the river head. The horizontal retention mechanism associated to BSHG within the spawning habitat favours growth and survival of fish larvae and the subsequent transport to nursery habitats.