MIDWATER FISHES OFF THE PACIFIC COAST OF BOSO PENINSULA, CENTRAL JAPAN - SPECIES COMPOSITION, ABUNDANCE, BIOMASS, AND ZOOGEOGRAPHIC AFFINITIES

Midwater fishes were collected by oblique hauls between the surface an d an average depth of 1290 m, using a 10-ft Isaacs-Kidd midwater trawl , at seven stations off the Pacific coast of Bose Peninsula, central J apan. A total of 1860 fishes (excluding larvae), representing 19 famil ies and 66 species, were collected, with a mean abundance and biomass of 565 inds and 278 g (wet weight) per 100 m(2) of ocean surface in th e upper 1000 m water column, respectively. Gonostomatids were most num erically abundant (75%), followed by myctophids (20%), melamphaids (1. 4%) and sternoptychids (0.9%), while myctophids dominated in total bio mass (47%), followed by gonostomatids (42%), melamphaids (3.1%) and ba thylagids (3.1%). Of these, the gonostomatid, Cyclothone atraria, rank ed top in both total abundance (52%) and biomass (26%). Zoogeographic grouping of the 66 species on the basis of centers of distributions/ab undance in relation to water masses indicated that tropical-subtropica l species were the most numerous overall (43 spp.), followed by wide-r anging (10 spp.), subarctic (6 spp.), pseudoceanic (6 spp.) and transi tional species (1 sp.). Except for the transitional species, all zooge ographic groups were represented by at least one of the six most abund ant species. Size-frequency distributions and other available informat ion suggested that the study area was located at an interface between peripheral breeding populations of the tropical-subtropical, subarctic and pseudoceanic species, being a consequence of both the adjacent la nd mass and hydrographic conditions of the area, where cold, less sali ne waters originating from the subarctic region advected below the mor e saline, warm Kuroshio current flowing northeastward along the penins ula.