Diel vertical migration of myctophid fishes (Family Myctophidae) in the transitional waters of the western North Pacific

The diel vertical migration patterns of adult myctophid fishes were determi ned in the transitional waters of the western North Pacific off Japan, usin g day-night sampling from 20 to 700 m depths with a commercial otter trawl in the summer of 1995. A total of 12 species belonging to 9 genera were col lected. Four patterns were recognized in the diel vertical migration of 11 of the 12 species. (1) Migrants showing clear day-night habitat separation with peak abundance above 200 m at night: Symbolophorus californiensis, Tar letonbeania taylori, Notoscopelus japonicus, Diaphus theta, Ceratoscopelus warmingi, and Diaphus gigas. (2) Semi-migrants, in which part of the popula tion often remains in the daytime habitat at night. The distribution depths of migratory and nonmigratory individuals do not overlap: Stenobrachius le ucopsarus. (3) Passive-migrants, in which there is no separation of day-nig ht habitats, but the upper limit of daytime distribution depth shifts to a shallower layer at night, probably as the fish follow migratory prey: Lampa nyctus jordani. (4) Nonmigrants: Stenobrachius nannochir, Lampanyctus regal is (> 140 mm SL), and Protomyctophum thompsoni. The day-night habitat tempe rature ranges are also given for the 11 species. No remarkable east-west di fferences were seen in the vertical migration patterns compared with previo us knowledge of eight of these species in the eastern Pacific. The diel mig ration patterns are newly described for three other species endemic to the western Pacific. The standing stock of myctophids in the study area was con servatively estimated at 18.5 +/- 4.7 g m(-2) (avg. +/- SD).