Distribution, hatch-date, growth, and mortality of larval Benthosema pterotum (Pisces: Myctophidae) in the shelf region of the East China Sea

Abstract

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).