Simulation of copepod biomass by a prey–predator model in Hiuchi-nada, central part of the Seto Inland Sea: does copepod biomass affect the recruitment to the shirasu (Japanese larval anchovy Engraulis japonicus) fishery?

Abstract

We have modeled the prey–predator dynamics between nutrients, phytoplankton, and copepods in Hiuchi-nada, central part of the Seto Inland Sea. The model parameters were estimated by stepwise regression using data sampled from 2001 to 2005. We re-created the fluctuations in copepod biomass in the spring–summer of 2001–2004 by model simulation and investigated the relationship between the re-created copepod biomass and anchovy Engraulis japonicus reproductive success rate in Hiuchi-nada. The anchovy reproductive success rate was proportional to the copepod biomass during the last 10 days of May, a period that immediately preceded anchovy recruitment. This relationship indicates that a possible key factor in the regulation of anchovy population levels is the fluctuation in abundance of the copepod assemblage and that the crucial period for anchovy recruitment in Hiuchi-nada would be the period just before anchovy recruitment to the shirasu (body length: approx. 20–35 mm) fishery. These results provide a potential framework for forecasting the anchovy recruitment level that is based on both larval abundance and survival rate as estimated from the biomass of copepods in the pre-recruitment period of anchovy.