Invasion status and reproduction of smallmouth bass Micropterus dolomieu in the Hinuma River upstream of Lake Hinuma, a Ramsar site in eastern Japan

Abstract

Invasion status of an invasive alien species, Micropterus dolomieu, was ex- amined in the main stream and its tributary (Iida River and Lake Kasama) of the Hinuma River system upstream of Lake Hinuma, a Ramser site in Ibaraki Prefecture, eastern Japan. A total of 228 individuals (6.3–295 mm in body length) including adult and larvae of this species were collected at seven sites immediately downstream of the tributary from June to September in both 2019 and 2020. A spawning nest with larvae and an adult was found at one site in the main river in June 2019. These results suggest that Micropterus dolomieu have expanded their distribution by continuing to reproduce within the river system.