Estimation of the maximum sustainable yield of giant grenadier <i>Albatrossia pectoralis</i> (Macrouridae) in the Russian Far East using Bayesian surplus production model JABBA

Abstract

Statistical estimates for the exploitable stock of giant grenadier are determined, by fishing zones in the Russian Far East, and interannual dynamics of the species biomass is considered using historical data on catches and abundance. The assessments relationship with reference points of the biomass dynamic models is examined for the first time. With using the Bayesian approach, a priori assumptions about virgin biomass, which were made earlier on results of scientific surveys extrapolated to unsurveyed areas, are accounted in JABBA model; some errors in the catch and abundance indices are revealed. The parameters of instantaneous rate of recruitment and initial depletion of population are determined. Overfishing is not detected yet in any fishing zone, but a negative trend of the biomass dynamics is noticed for the Western Bering Sea fishing zone since 2015 (if the stock estimations based on surveys are realistic). The decline is reasoned by implementation of too high target for exploitation rate of vulnerable biomass (φF = 0.10) that is higher than such target for other fishing zones (< 0.08 or even 0.01 for the stocks exploited with the total allowable catch limits). That’s why annual catches exceeded the surplus production in the Western Bering Sea fishing zone in 2012 and since 2015 to nowadays. The sum of median estimations for the maximum sustainable yields in all fishing zones is about 47.4 . 103 t that exceeds the values of total annual catch. The instantaneous rate of recruitment is almost equal in the neighboring fishing zones in the western Bering Sea and at East Kamchatka (0.086–0.085 by median, with 95 % credible intervals from 0.05 to 0.14) and is much higher at Kuril Islands with the maximum in the North-Kuril fishing zone. The latter case is possibly conditioned by partially external recruitment. Therefore, population structure of giant grenadier should be clarified for correct modeling of the recruitment; until then, the stocks assessments by fishing zones are available.