On the occurrence of the Taiwan angel shark, Squatina formosa Shen & Ting, 1972 (Chondrichthyes, Squatinidae) from Japan

Abstract

In the Pacific, most angel sharks display rather limited geographic distributions. Recent findings of three specimens of the Taiwan angel shark, Squatina formosa, from Tosa Bay, Kochi Prefecture, Japan enlarges the known geographic range of this species considerably. So far, this species only has been known from Taiwan. Other records might be considered misidentifications. The three specimens that form the focus of this study are from the central Tosa Bay (Province of Kochi) in SE Japan. They were collected with otter trawls in ca. 200 m depth in May and June 2008. Although these specimens differ slightly from the holotype from Taiwan in some features, their identification as belonging to Squatina formosa is well supported by the colour pattern and a suite of morphological characters such as shape and meristics of the upper lip arch, the shape of the caudal fin lobe and the shape and size of the pectoral, pelvic and dorsal fins. Additionally, the taxonomic identification is strongly supported by molecular and data by comparison with a specimen from Taiwan and previously published data. The mtDNA difference between the Taiwanese and Japanese populations is 0.2 % and is most likely related to a descent from a postulated original population some 10,000 years ago. It is most likely that this species occurs from the small Batan Islands, along the Ryukyu Trench and the corresponding Ryukyu Islands from Taiwan north along the south-eastern mainland coast of Japan. This species seemingly occurs along the Kuroshio Current and is absent from cold-influenced waters (e.g. western Taiwan, China and Japan seas). The recent finding of this species in Tosa Bay most probably is due to range extension because of globally increasing sea water temperatures.