Dear colleagues: We hereby inform you that we extended thesis submission for the X International Conference "Marine mammals of the Holarctic" dedicated to the memory of Professor Alexei Vladimirovich Yablokov, until July 15, 2018. Publication of abstracts is possible only if the registration fee is paid till July 31, 2018. Extended Materials are prepared and submitted in accordance with the required Guidance before July 31, approved by the Organizing Committee and not requiring significant revision or editing, will be included into the 1st volume of the Collection of Conference Papers, the electronic version of which is planned to be published in early 2019 . Materials requiring substantial revision and/or editing will be included on the 2nd volume of the Collection of Conference Papers, electronic version of which is planned to be released in the second half of 2019. All Extended Materials should be submitted before October 31, 2018. Registration of participants and submission of the abstracts and extended materials to the Collection of Scientific Papers are accomplished through the web http://marmam.ru/en/conference/mmg-x/. You can find extended Materials from the previous Conferences here: http://marmam.ru/en/conference/. See the preliminary Conference program on web-page: http://marmam.ru/en/conference/program/.