Formation of the Fauna of Cartilaginous Fishes of the Emperor Seamount Chain

Abstract

The presented data on distribution of cartilaginous fishes in the northern Pacific Ocean show that the core of the fauna of the Emperor Seamount Chain includes Indo-West Pacific species that inhabited the ridge from the coast of Asia. Epipelagic species are not permanent residents of the region, but annually migrate from the mainland to the ocean together with common abundant fish species that form their food supply. Sharks and chimaeras of the meso-benthopelagic zone constitute the basis of permanent cartilaginous fish communities of the seamounts of the Northwestern Pacific. Representatives of the lower meso-benthopelagic zone populated the Hawaiian and Emperor Seamount Chains along with the Markus-Necker Ridge. Less deep-sea, but adapted to a fairly long-term dwelling in the water column in the adult state, the species of the upper meso-benthopelagic zone, spreading towards the ridge, covered a distance of about 3000 km in the pelagic zone. Probably, some sharks of the lower meso-benthopelagic zone could inhabit the underwater mountains of the Emperor Seamount Chain in the same way. The low endemicity of cartilaginous fishes in the considered area (5%) and the presence of identical and closely related species in southern Japan do not allow us to regard migrations to the Emperor ridge as rare, with the exception of sharks of the genera Squalus and Centroscyllium, which diverged on the seamounts to the level of new species.