Isolated Fluvial Population of Dolly Varden Salvelinus malma on Bering Island (Commander Islands)

Abstract

For the first time on Bering Island (Commander Islands), an isolated population of northern Dolly Varden Salvelinus malma has been found. It inhabits only the Vodopadnaya River, which is separated from the sea by an insuperable for migratory fish waterfall, 6 m high, and does not house any other fish species. The Dolly Varden charr of isolated population are stunted with lifespan up to 12 years; the size of females, fecundity, and diameter of eggs are smaller than in the anadromous northern Dolly Varden from other rivers on Bering Island. Isolated population of the Vodopadnaya River is a derivative of the anadromous Dolly Varden; it retained the main identifying features of the species, although the size of the fish is significantly larger in comparison to other isolated brook populations of the range, which are commonly represented by small individuals with a juvenile appearance and a short lifespan. Probably, the origin of an isolated charr population in the Vodopadnaya River resulted from the rise of the lithospheric block in the lower reaches of the river during a strong earthquake in the period from 12 to 4–3 thousand years ago, most likely about 9.5 thousand years ago. The isolated population of charrs is characterized by a significant decrease in the indices of genetic diversity in comparison with the anadromous Dolly Varden of the Commander Islands. A significant level of genetic divergence (FST = 0.248) between isolated and anadromous Dolly Varden char on Bering Island has been revealed. The discovered isolate population according to some morphological and genetic characteristics can be considered as a unique unit of diversity both among the Commander Islands and among other populations of the species.