Strontium isotope mapping and its application to study the fish life history (Salminus brasiliensis) in semi-fragmented rivers (La Plata Basin, South America)

Abstract

Salminus brasiliensis is one of the largest and most important commercial and sporting fish species in South America, of which little is known about its habitat use, especially in semi-fragmented rivers. The aims of this study were to expand the water 87Sr/86Sr baseline of the La Plata Basin, and to study the migratory patterns of S. brasiliensis from Paraná dam-free stretch and a representative tributary semi-fragmented using otolith isotopic chemistry. Water samples were collected at 10 sites on the upper Paraná River and two sites on the middle and lower Carcarañá Basin (tributary of the lower Paraná River). Fourteen fish were caught in the upper Paraná River and 13 in two sites of the middle and lower Carcarañá Basin. 87Sr/86Sr was measured in water and otolith core-to-edge transect by MC-ICPMS and LA-MC-ICPMS, respectively. Water results were incorporated into a dataset with 53 other sampling points from the La Plata Basin and subjected to a cluster analysis, which resulted in nine differentiable chemical signatures. Discriminant analysis confirmed the presence of at least eight contrasting isotopic signals. Based on the otolith core 87Sr/86Sr, four individuals from the upper Paraná River were classified as originating from Paraguay sub-basin, while the rest were assigned to Paraná River. All fish from the Carcarañá sub-basin were classified as originating from the Paraná River, except two individuals which were assigned to the Carcarañá sub-basin. Results indicated that the fish run up the Carcarañá sub-basin overcoming up to three open spillways, and could live there for years and even reproduce. However, the Paraná River had the largest contribution to the fish caught in both the upper Paraná River and the Carcarañá sub-basin.