Chapter 6: Ocean Ecology of Masu (Cherry) Salmon
Kentaro Morita, Toru Nagasawa, and Yasuyuki Miyakoshi
Masu Salmon, also known as Cherry Salmon, is a member of the genus Oncorhynchus and is endemic to Asia. Their restricted distribution is unique, because all five of the other Pacific salmon species are distributed along both sides of the Pacific Rim. To date, four subspecies have been identified within the Masu Salmon group (Figure 1.1). Of these, Masu Salmon (Oncorhynchus masou masou) are the most widely distributed, with a range that extends throughout Far East Asia (Figure 1.2). Amago Salmon (O. masou ishikawae) are distributed along the Pacific coast of western Japan. Biwa Salmon (O. masou subsp.) are only found in Lake Biwa and its inlet streams. Formosa Landlocked Salmon (O. masou formosanus) are found only in the headwaters of the Tachia (Dajia) River, Taiwan (N 24° 10–25’), which is also the southern limit of the natural range of the genus Oncorhynchus on the western side of the Pacific Rim (Yan 2000).
The common name “Cherry Salmon” probably originated from the Japanese sakura-masu. Sakura means “cherry” (plants of the genus Prunus) and masu means “trout.” The name is thought to relate to the return timing of adults that is often coincident with the season of cherry blossoms in northern Japan (April and May) and/or the resemblance of the nuptial colors of spawning adults to that of the color of cherry flowers. Although Kato (1991) classified Amago Salmon as O. rhodurus, most recent studies classify Amago Salmon as O. masou ishikawae (e.g., Oohara and Okazaki 1996; Gwo et al. 2008). Historical confusion of this complex is reviewed by Kimura (1990).
The natural distribution of these subspecies did not overlap historically (Fujioka 2009; Tsuboi 2014). However, there is now considerable overlap among the subspecies as a result of artificial transplantation, resulting in increased incidence of hybridization (Tago 2002; Yamazaki et al. 2005; Kuwahara et al. 2012).