Fish Species Diversity, Distribution, and Dispersal in the Rivers of the Penzhina Bay Catchment Area

New expedition data, analysis of unpublished archives, and questionnaire information made it possible to clarify the ichthyofauna species diversity and to assess the distribution of freshwater, anadromous, and semianadromous fishes in the largest and some small rivers of the Penzhina Bay basin. The results indicate that the lower reaches of the rivers are inhabited by 11 anadromous species and ten freshwater species, including five whitefish species. The most diverse freshwater fish complex is revealed off the northern coast of the Sea of Okhotsk. Freshwater fauna exchange under modern conditions is possible through the sources of the largest river systems during the most severe spring floods (both within the Penzhina Bay basin and in adjacent basins of the East Siberian and Bering seas). In the apex of Penzhina Bay, the modern sea-coast regional dispersal takes place only between the rivers with joint mouths. This path is provided by extremely strong tidal currents and considerable freshening of coastal areas during the floods.