We examined the distribution, hatch-date, growth, and mortality of larval
Benthosema pterotum, a dominant pseudoceanic myctophid
in the shelf region of the East China Sea, during early autumn when the main
spawning has been predicted. This species is a key species in the food web
of this area. Larvae were abundant in the area south of Cheju Island
(60–80 m depth), corresponding with the adult habitat. Occurrence of the
larvae was restricted to the onshore side of the shelf-break salinity front,
indicating that this front acted as a barrier restricting the offshore
dispersion of the larvae. In the area where the larvae occurred, a cyclonic
eddy is formed, which is considered to limit the dispersal of the larvae,
enabling them to recruit into the area of adult habitat. Modes of hatch-date
appeared from late August to early September and from mid to late September,
suggesting that large-scale spawning events occurred at least twice during
the spawning season. Since the modes coincided with the new moon period,
B. pterotum is suggested to spawn periodically once a
month around the new moon, resulting in efficient mating and fertilization.
Mean absolute growth rate (0.26 mm d−1) and weight-specific
growth rate (18.8% of dry body weight d−1) were higher than
previously reported values of other subtropical–tropical myctophids, which
would be related to the high food availability in the study area. Daily
instantaneous mortality coefficient during the first two weeks after
hatching was estimated to be 0.28 d−1 (equivalent to 24.7%
mortality d−1).