Two-species population dynamics model for Japanese sardine Sardinops melanostictus and chub mackerel Scomber japonicus off the Pacific coast of Japan

Abstract

A two-species population dynamics model was constructed for Japanese sardine Sardinops melanostictus and chub mackerel Scomber japonicus off the Pacific coast of Japan. Japanese sardine and chub mackerel have exhibited dramatic changes in stock abundance. The simulation captures these fluctuations clearly for the period 1976–2000 using this model. This population dynamics model has three sub-models: Stock, RecruitmentOfSardine and RecruitmentOfChubMackerel. The sub-model Stock is an age-structured model which calculates the natural mortality, catch, and spawning biomass of sardine and chub mackerel, respectively. The sub-model RecruitmentOfSardine is comprised of two sub-models: a spawning model Spawning and a spatial model Ocean of the early life stages. The sub-model RecruitmentOfChubMackerel is a recruitment model which receives the spawning biomass of chub mackerel and the stock biomass of sardine from the sub-model Stock and calculates the recruitment number of chub mackerel by an extended Ricker spawner–recruit curve which incorporates the water temperature of the spawning area and the stock biomass of sardine. The initial simulations were carried out using data of the age-specific stock number (number of individuals) and the data of the individual age-specific weight of sardine and chub mackerel in 1976. As the output data of 1977–2000, yearly egg data of sardine, recruitment data of chub mackerel, stock data and catch data were obtained. In this work, using the two-species population dynamics model, we investigated the influence of the fishery and the water temperature on the biomass of the two fishes. Our simulation revealed that the simulated chub mackerel stock increased again after 1995 in the absence of catch, however, the sardine stock decreased after the late-1980s even in the absence of catch. In the case of lower water temperature, the simulated sardine stock increased and the simulated chub mackerel stock decreased. It was expected that the fluctuations of two fishes population were re-synchronized after a certain period of time by effects of the water temperature. Our simulation indicated that the water temperature could influence the different stock fluctuations of sardine and chub mackerel in the case that the initial status of these fishes were very different.