87Sr/86Sr, Sr and Ca concentration, and salinity of water samples from the estuaries of the Gambia River, Sine-Saloum, and Volta River, 2017

Modern sub-surface water samples and the otoliths of catfish (Carlarius parkii and Chrysichthys nigrodigitatus) collected from the estuaries of the Gambia River (The Gambia), Sine-Saloum (Senegal), and Volta River (Ghana) in 2017 were analysed to investigate relationships between the Sr geochemistry and salinity. 87Sr/86Sr, Sr concentration, and salinity measured in water samples collected along the estuarine salinity gradients were used to establish mixing models describing their relationships. Bulk catfish otolith 87Sr/86Sr measurements were used to estimate habitat salinity of the fish based on these mixing models. Catch data (total length, fork length, weight) of catfish were recorded and used to estimate their age. Fish ages were further estimated based on otolith annuli.