Relative abundance index as an operational assessment of the state of the king blue crab stock in the Shelikhov Bay of Okhotsk Sea

Abstract

The material of spring registration surveys of the blue king crab Paralithodes platypus conducted in the Shelikhov Bay of the Okhotsk Sea from 2007 to 2019 is presented. It is proposed to use the relative abundance index (I%N) for a quick assessment of the characterizing state of the stock of the exploited population. The index I%N is defined as the ratio of the number of a separate functional group of the crab to the maximum number for this group of crab in the study period, expressed as a percentage. A similar algorithm was used to determine the index of the relative density of the distribution of crabs (I%P) and the index of the relative average daily catch of fishing vessels for the first half of the year (I%M). When comparing the relative indices I%N, I%P, I%M, the most convincing was the relative population index I%N. To assess the stock status of the studied functional group of crabs in the values of the index I%N, it was proposed to distinguish 4 quartiles (interval 25 units): 1st quartile (Q1) I%N <75 stock condition is good; 2nd quartile (Q2) I%N = 51–75 stock condition is satisfactory or relatively stable; 3rd quartile (Q3) I%N 26–50 stock status uncertain; 4th quartile (Q4) I%N ≤25 stock status is unsatisfactory or depressive. The boundary values between quartiles Q1–Q2, Q2–Q3, and Q3–Q4 are I%N values of 75, 50, and 25, respectively. The dynamics of the I%N index in the studied time period reflects the real process taking place in the fishing unit of the stock based only on empirical data.