Biggest seaports of Russian Empire by tonnage of visiting ships in 1912 (the figures for tonnage are in thousands of tonns)

Reference 1: Tonnage.

Reference 2: Riga, Kerch, Arkhangelsk, Feodosia, Onega, Mariupol, Evpatoria, Sukhum, Izmail, Astara, Vladivostok, Nikolayevsk-on-Amur, Astrakhan, Baku, Reni, Krasnovodsk, Batum, Poti, Berdyansk, Novorossiysk, Nikolayev, Libava, Odessa, Narva, Kherson, Revel, Sevastopol, Saint Petersburg, Genichensk, Pernov, Taganrog and Vindava.

Source: http://en.wikipedia.org/wiki/Russian_Empire