Stock assessment of the Sea of Japan stock of red snow crab Chionoecetes japonicus

Abstract

 An age, sex and stage structured model of stock dynamics into which the effect of terminal molt of individual growth is incorporated was applied to Japanese data of the Sea of Japan stock of red snow crab in order to estimate stock sizes from 1978 to 2018. The model of the stock by sex consisted of an immature component in which growth of body length continued and a mature component in which the growth stopped by terminal molt. The data sets used for estimations were the series of catch over the years, that of abundance index, average body weight in catch over 2000-2018, series of index of body weight and some biological parameter values. Using a given fishing coefficient and stable age-composition in the first year of data, annual stock sizes in subsequent years were computed using those values, biological parameters and deterministic equations in the model. Unknown parameters were estimated using the least squares method, and the parametric bootstrap method was used to estimate variances of parameter estimates. The results of estimations showed that point estimates of spawning stock biomass in 2015 were 204 (CI: 184-224) thousand tons. Modifications and issues concerning the estimations in the future are discussed.