Content: The grooved carpet shell (Ruditapes decussatus) and the common cockle (Cerastoderma edule) are exploited by professional and non-professional fishermen at the Oka estuary (Basque Country, northern Spain). In order to evaluate this exploitation a research on the evolution of both species has been conducted since 1998. Species habitat modeling is a tool increasingly used as a complement to the management of natural resources. In this investigation Generalized Additive Models (GAM) have been applied to estimate the density and biomass for both species in the entire Oka estuary. Predictive models of Ruditapes density and biomass explain 52.4% and 58.5% of variance and have a validation of 37.6% and 34.4%, respectively, while in the case of Cerastoderma predictive models explain 34.2% and 22.1% of variance and have a validation of 197% and 25.1%, for the density and the biomass, respectively. The models can be improved in the future by adding new environmental variables and with a better coverage of biological and physical samples (e.g. sediment data), but even so, the results obtained are consistent with the resource assessment data obtained previously.