The black and gold howler monkey (Alouatta caraya) is a neotropical primate that faces the highest capture pressure for illegal trade in Argentina. We evaluate the applicability of genetic assignment tests based on microsatellite genotypic data to accurately assign individuals to their site of origin. The search was conducted on a genetic database to determine the nearest sampled population or to associate them to three clusters described here for the Argentinean populations of A. caraya. We correctly assign 73% of the individuals in the database to nearest population of origin, and 93.3% to their cluster of origin. With this database, we were able to determine the probable origin of 17 confiscated individuals, 12 of which were reintroduced in the province of Misiones and 5 confiscated individuals reintroduced in the province of Santa Fe. Moreover, we also determined the probable origin of 3 individuals found dead in cities in northern Argentina. This approach highlights the relevance of generating genotype indexing databases of species to assist with in-situ and exsitu conservation and management programs. Our results underscore the importance of knowing the origin of individuals for reintroduction and/or species recovery programs and to pinpoint the hotspots of illegal capture of various species.

The fish diversity and the main environmental factors affecting the spatial distribution of species, life history stages and community structure in the Río de la Plata (RdP) and adjacent waters are reviewed and analysed, with emphasis on the functional guild classification. The functional guild classification indicated that most species in the RdP were marine stragglers, zoobenthivores and oviparous species, although the biomass was dominated by estuarine species. Salinity had a stronger influence than temperature on the spatial pattern for all life stages, shallower and fresher waters are the preferred habitats of neonates and juveniles. During the breeding season (spring-summer), adults showed an intrusion into the inner part of RdP or to its adjacent nearshore waters from the offshore waters for spawning or mating, respectively. Variations in river discharge and wind patterns greatly affected the spatial extent of estuarine water, which ultimately influenced the domain of the main life-history stages (juveniles or adults) for both marine and estuarine fishes, as well as species and fish assemblage composition. The strong environmental gradient restricts some species and life-history stages to a particular section and defines three main fish assemblage areas. The composition of the fish assemblage is indicative of the recruitment of freshwater and marine species to the estuary in opposite ways, determined by the vertical stratification. Seasonal changes in the species composition were related to migration as a result of salinity and temperature variations and reproductive migrations to spawning and mating areas. This overview reveals that the RdP is under environmental variations that are likely to produce modifications to fish distribution and abundance that affect its fisheries. This context plus fish stock declines and changes in exploitation patterns could amplify the magnitude of the variations in the fisheries resources availability and affect the sustainability of fishing communities.

Summary We established the presence of Eucinostomus at the Río de la Plata Estuary (36°17′74′′S–56°46′68′′W). The report is based on specimen of 191.6 mm. total length, captured in shallow, warm and brackish water with sandy bottom. This is southernmost record for the Southwest Atlantic Ocean, and appears related with an event of low discharge of the Río de la Plata.