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

Abstract

The diel vertical migration patterns of adult myctophid fishes were determined in the transitional waters of the western North Pacific off Japan, using 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 collected. 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, Tarletonbeania taylori, Notoscopelus japonicus, Diaphus theta, Ceratoscopelus warmingi, and Diaphus gigas. (2) Semi‐migrants, in which part of the population often remains in the daytime habitat at night. The distribution depths of migratory and nonmigratory individuals do not overlap: Stenobrachius leucopsarus. (3) Passive‐migrants, in which there is no separation of day–night habitats, but the upper limit of daytime distribution depth shifts to a shallower layer at night, probably as the fish follow migratory prey: Lampanyctus jordani. (4) Nonmigrants: Stenobrachius nannochir, Lampanyctus regalis (> 140 mm SL), and Protomyctophum thompsoni. The day–night habitat temperature ranges are also given for the 11 species. No remarkable east–west differences were seen in the vertical migration patterns compared with previous knowledge of eight of these species in the eastern Pacific. The diel migration patterns are newly described for three other species endemic to the western Pacific. The standing stock of myctophids in the study area was conservatively estimated at 18.5 ± 4.7 g m−2 (avg. ± SD).

Larval feeding habits of Diaphus theta, Protomyctophum thompsoni, and Tarletonbeania taylori (Pisces: Myctophidae) in the transition region of the western North Pacific

“…Diaphus theta and Tarletonbeania taylori begin diel vertical migration and actively feed in the epipelagic layer at night after transformation from larvae to juveniles (Pearcy et al 1977, Watanabe et al 1999, Moku et al 2000. In the highly productive subarctic and transition regions, adult D. theta feed actively, both during the daytime in the mesopelagic and at night in the epipelagic zones (Paxton 1967.…”

“…Thus, after transformation to juveniles, D. theta change their feeding periodicity from diurnal to all-day feeding, while T. taylori shift their feeding from diurnal to nocturnal after transformation to juveniles. Proto- myctophum thompsoni is a non-migrant species that begins to stay in the 200 to 400 m layer from the juvenile stage (Pearcy et al 1977, Watanabe et al 1999). Adult P. thompsoni feed both during the day and at night in the mesopelagic zone.…”

“…Diaphus theta, Protomyctophum thompsoni, and Tarletonbeania taylori are the dominant myctophid fishes in the transition and subarctic regions of the North Pacific (Bekker 1967, Wisner 1976, Pearcy et al 1979, Willis et al 1988, Beamish et al 1999, Watanabe et al 1999. The larvae of these species are distributed in the productive upper 200 m layer of the transition region, both during the day and at night (Sassa 2001, Tsukamoto et al 2001.…”

“…The larvae of these species are distributed in the productive upper 200 m layer of the transition region, both during the day and at night (Sassa 2001, Tsukamoto et al 2001. After transformation from larvae to juveniles, D. theta and T. taylori begin diel vertical migrations, while P. thompsoni shows no diel vertical migration and remains primarily in the upper mesopelagic layer at a depth of 200 to 400 m (Pearcy et al 1977, Watanabe et al 1999.…”

Importance of walleye pollock (Theragra chalcogramma) to wintering ribbon seals (Phoca fasciata) in Nemuro Strait, Hokkaido Japan

“…Saffron cod (Eleginus gracillis) found only in the stomachs of young seals (Table 4) are distributed in shallower waters than walleye pollock (Nagasawa and Torisawa 1991). Pinpoint lanternfish (Lampanyctus regalis) found only in the stomachs of adults (Table 4) are distributed in much deeper waters and show little diel vertical migration pattern (Watanabe et al 1999). Because diving ability depends on body size (Snyder 1983;Kooyman 1989), larger adult seals can dive longer and therefore deeper than smaller young seals.…”