Distribution and Synonymy in the Pacific Ocean, and Variation, of the Greenland Halibut, Reinhardtius hippoglossoides (Walbaum)

Abstract

Long known in the Pacific Ocean from a single specimen from east-central Japan, the very distinctive flatfish genus Reinhardtius has been shown since 1930 to maintain a population of commercial significance from northern Japan to northwestern Bering Sea. It is now found to be common also in eastern Bering Sea, and to occur also just south of the tip of the Alaska Peninsula, in northern and central California, and even at the extreme north of Baja California, Mexico. Japan and the Californias appear to be inhabited by non-breeding expatriates, whose wanderings are attributable to the free-swimming habits and prolonged early pelagic development of the species. Lack of records between the Alaska Peninsula and California may possibly indicate actual absence, attributable to current pattern. Analysis of the only morphometric characters thought to be indicative of subspecific differentiation between the Pacific and Atlantic stocks discloses no basis for such separation, nor do any meristic characters disclose such a basis. The single species Reinhardtius hippoglossoides is therefore regarded as a uniquely undifferentiated amphiboreal taxon. The chief distinction between the ocean stocks lies in the number of vertebrae, but the differentiation (probably genetic) is not beyond the racial level. The difference in vertebral numbers, surprisingly, is not paralleled by a difference in numbers of dorsal or anal rays; nor is there any marked correlation between vertebral and ray numbers. As expected, the numbers of dorsal and anal rays are found to be positively correlated, and the number of precaudal and caudal vertebrae to be negatively correlated. In this flatfish of relatively limited asymmetry the numbers of rays are virtually identical in the two pectoral fins. Two reversed examples of the species are reported.