Verevkin, Mikhail, and Vadim Vysotsky. “Current Status of the Ladoga Ringed Seal <em>Pusa Hispida ladogensis</Em&gt; (Nordquist, 1899)”. Biological Communications0, no. 4 (December 30, 2013): 14–25. Accessed June 17, 2021. https://biocomm.spbu.ru/article/view/1321.