SIZE COMPOSITION AND GROWTH RATES OF BLUE KING CRAB PARALITHODES PLATYPUS BRANDT, 1850 IN THE RUSSIAN SECTOR OF THE BERING SEA

Size composition and growth rate of blue king crab males are analyzed on the data of 8 bottom trawl surveys conducted in the western Bering Sea in summer-fall seasons within the period from 2005 to 2017. Significant changes in size structure of this population are revealed. Portion of commercial males was the lowest (18.7 %) in 2010 because of the strong yearclass appeared in the catches in 2005, when its males carapace had the width 20–40 mm, that provided in 2008–2010 the percentage of juveniles with the size < 100 mm about 59–60 %. Then this strong year-class reached the commercial size, so the portion of commercial males increased to 66 % in 2014 and to 85 % in 2015–2016. The portion of juveniles was extremely small (3.1–6.5 %) in these years. The portion of commercial males had reduced again to 67 % in 2017 because of a new strong year-class appearance that provided the juveniles percentage increasing to 24.6 %. The mean size of commercial males has increased since 2012 in 18 mm and reached the value of 160.4 mm in 2017. Age of the crab males entry into the commercial cohort is estimated as 8 years. The observed cyclic changes in size composition of blue king crab and estimated value of its growth rate indicate indirectly a good and stable state of its population in the western Bering Sea.

Survival, growth, and morphology of blue king crabs: effect of ocean acidification decreases with exposure time

Ocean acidification is an altering marine carbonate chemistry resulting in potential effects to marine life. In this study, we determine the effects of decreased pH on the morphology, growth, and survival of juvenile blue king crab, Paralithodes platypus. Crabs were reared at three pH levels: ambient (control, pH ∼8.1), pH 7.8, and pH 7.5, for 1 year and monitored for morphological changes, survival, and growth. Exposure to seawater at pH 7.8 had no effect on morphology or mortality and had only a minor effect on growth compared with the ambient treatment. However, exposure to seawater at pH 7.5 substantially increased mortality and decreased growth compared with the ambient treatment. The best fit model of mortality rate at pH 7.5 showed an initially high mortality rate, which dropped to become comparable to the mortality rate in the other treatments. This suggests phenotypic variability or plasticity in juveniles and may indicate acclimation by blue king crab to ocean acidification. As such, blue king crab may have scope for evolutionary adaptation in response to gradually changing pH levels. However, effects on other life-history stages, sub-lethal effects, carryover or transgenerational effects, and interactions with other stressors, such as increased temperature, still need to be investigated.

Application of the virtual population model in the bio-economic model of long-term dynamics for exploited population of commercial invertebrates

The virtual population analysis is used for complex tasks of bio-economic modeling of long-term dynamics for exploited population of commercial invertebrates, as blue king crab in the western Bering Sea. This method is based on the data of landings for the period exceeding the life span for the studied stock and provides guaranteed estimations of the age cohorts abundance. The assessments of the blue king crab stock dynamics are used in the economic block of the model that provides market assessment of the resource for evaluation of final cost for the manufactured goods. Two blocks of the bio-economic model allow to calculate a future income from exploitation of the resource that is necessary for planning of economical activity in fisheries industry.