Härkönen, T.; Stenman, O.; Jüssi, M.; Jüssi, I.; Sagitov, R.; Verevkin, M. Population Size and Distribution of the Baltic Ringed Seal (Phoca Hispida Botnica). NAMMCOSP 1998, 1, 167-180. https://doi.org/10.7557/3.2986.