Spatial variability of the size structure of the blue king crab in the Northern part of the Sea of Okhotsk

   The purpose of this study was to identify size groups of the blue king crab (Paralithodes platypus) in the Northern part of the Sea of Okhotsk.

   Material –  тdata from trap catches collected between 1992 and 2020. A total of 1,591 samples of males and 476 samples of females of the blue king crab were analyzed.

   Methods – the optimal number of clusters partitioning the dataset on the size composition of the blue king crab was determined using the silhouette coefficient. Cluster analysis was performed using the k-medoids method. The complete dataset was divided into three parts: a training set, a test set, and a hold-out set. After clustering, the results were mapped, and the study area was subdivided into regions according to the highest concentration of stations belonging to each cluster.

   Scientific novelty – this study is the first to apply statistical methods for identifying size groups of the blue king crab in the northern Sea of Okhotsk.

   Results – the study revealed the presence of two size groups of the blue king crab for both males and females. Spatial segregation of these groups was observed, being pronounced in males and less distinct in females. The boundary separating the male size groups is the meridian 152° E: west of this line, only small- sized males occur, whereas east of it, large-sized individuals predominate. In females, the differences increase gradually; however, since most samples east of 152° E contain large-sized females, this meridian can be considered, as in males, a tentative boundary between the two size groups.

   Scientific significance – the developed statistical analysis procedure of size composition incorporating spatial factors revealed intrapopulation heterogeneity in the distribution of different- sized crab individuals.

   Practical significance – identifying size groups of the blue king crab can contribute to improving the management efficiency of this biological resource.

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