Spatial co-occurrence of two Sciaenid species (Micropogonias fuernieri and Cynocion guatucupa) subject to fishing in the Rí­­o de La Plata and oceanic coast of Uruguay: ecological or technological interdependence?

Abstract

The whitemouth croaker (Micropogonias furnieri) and striped weakfish (Cynoscion guatucupa) are the most important resource of coastal fisheries in the Southwest Atlantic Ocean and particularly in Rí­­o de la Plata estuary. The aim of this study is to analyze the spatial and temporal co-occurrence of both species in relation to the estimates of density, length structure and immature-mature individuals using research vessel data from the spring of 1991-1995 and 2007. A positive tendency for co-occurrence and species overlap occurred in more than 53% of fishing trawls, either significantly or with predominance of whitemouth croaker or striped weakfish. Differences between the spatial distributions of both species during the spring in the study area were found for all years with the exception of 1992, a supposed consequence of increased river discharge related to El Nií­±o/Southern Oscillation (ENSO) effects. In fishing hauls where significant species overlap occurred, length composition showed that whitemouth croaker adults spatially co-occurred with juveniles of striped weakfish. The nonrandom spatial segregation of both species as consequence of habitat heterogeneity and differential feeding habits did not support the ecological interdependence hypothesis. Rather, according to the trawler fleet that operates and directs the fishing effort towards these two target species, there may be evidence of technological interdependence. Fishing trawls may affect different length classes with different environmental requirements at different stages of their life history. These aspects should be considered when weighing different fisheries management options, related to the spawning areas and genetic management units of both species.