Estimation of Size-Dependent Mortality of Chub Mackerel (Scomber japonicus) Based on Their Fecundity

We estimated the size-dependent mortality of chub mackerel, Scomber japonicus, for the entire life stages from egg to adult by using a Leslie matrix model based on their fecundity, assuming the steady-state and the bigger-is-better hypothesis. The daily body size was determined by the temperature-dependent Gompertz–Laird and the temperature-independent von Bertalanffy growth equation. The derived constant for size-specific instantaneous mortality was 0.11 day−1 cm in fork length. The estimates of age-specific mortality ranged from 8.04 yr−1 for age 0 to 1.04 yr−1 for age 6 + . Our simulations showed that as the growth rate increases, the mortality decreases, and the recruitment level increases as the ambient water temperature from the egg to larval stages increases from 14 to 22 °C. Comparisons of the length frequencies derived from our Leslie matrix with the catch data suggested that our theoretically derived mortality is reliable enough for the purpose of stock assessment for fisheries management. We expect our approach will be applied in developing bio-physical coupling models for evaluating and projecting the influences of climate change and warming ocean on fish stocks.