Daily growth of young-of-the-year largehead hairtail (Trichiurus japonicus) in relation to environmental variables in the East China Sea

Abstract

Abstract Largehead hairtail (Trichiurus japonicus) is an important fish species in China Sea, characterized by wide distribution, extensive migration, long spawning period and high economic value. The East China Sea is one of the typical over-exploited ecosystems in the world where most of the fish populations are overfished. In spite of high fishing pressure over an extended period, the catch of largehead hairtail showed an increasing trend in recent years. In this study, using otolith microstructure analysis for daily ageing, we explored spawning seasonality of largehead hairtail and daily growth of young-of-the-year (YoY) largehead hairtail in the East China Sea. Spawning seasonality of largehead hairtail was found to be nearly year round with two dominant seasons: autumn and spring. The gradient forest method was used to identify the relative importance of various environmental variables in relation to daily growth of YoY largehead hairtail; the first six most important environmental variables were subsequently analyzed using generalized additive models for their specific associations with daily growth of YoY largehead hairtail. Results show that sea surface temperature (SST), sea bottom temperature (SBT), temperature difference (TD) between surface and bottom water, and mixed layer depth (MLD) are the most important variables for daily growth of almost all month cohorts. In addition, the consistent interactive effects of water temperature (SST and SBT) and MLD suggest that daily growth of YoY largehead hairtail is influenced by the interactive effects of water temperature and nutrient supplies. This study highlights the importance of understanding the reproductive process and early growth of largehead hairtail in relation to environmental variables, which has important implications for the sustainable management and utilization of largehead hairtail in the over-exploited China Seas.