Estimation of the spawning biomass of myctophids based on larval production and reproductive parameters: The case study of Benthosema pterotum in the East China Sea

Abstract

This study estimated the spawning biomass of a myctophid by applying the daily egg production method (DEPM) based on data of larval fish surveys and reproductive parameters. Benthosema pterotum in the central part of the East China Sea shelf was used as the model species, as ecological and reproductive data are available in the literature. This study used data of the larvae and adults sampled in late summer when the primary spawning occurs. Daily egg production was estimated by back-projection of the daily production of larvae at hatching by 10 h, assuming that the mortality rate during the egg stage is the same to that of the larval stage. This study determined the sex ratio, batch fecundity, and spawning fraction. As a result, spawning biomass of B. pterotum in the East China Sea shelf was estimated to be 9036 tons. The study also assesses and discusses several sources of potential uncertainty. The relative sensitivity of estimates of spawning biomass to variations in each parameter showed a four fold difference between the lowest and highest estimates (4066-16 265 tons). Since this was comparable to the biomass estimated by a swept-area trawl survey, the approximate estimation of biomass would be possible by applying this method. Considering that larval fish surveys have been conducted in the world's oceans and myctophids have always dominated in the samples, application of the DEPM is a potential option for estimating the order of magnitude of the biomass of myctophids.