Evaluation of the productivity of walleye pollock generations in the northern Sea of Okhotsk

Abstract

Based on data on the abundances of various age groups in the northern Sea of Okhotsk in 1984–2008, the productivity of 33 generations of walleye pollock born between 1975 and 2007 was evaluated in two ways. The first approach allowed a retrospective estimation by abundance of the first nine one-year age groups, and the second one was a perspective estimation using the abundance index of the nearest recruitment—3- and 4-year-olds—that enabled us to evaluate the productivity of a generation before it enters into spawning and commercial stocks. These productivity estimates were compared to the data of annual catches and the dynamics of spawning stock for many years. A high value of walleye pollock stock was shown to be supported by several productive and highly productive generations, a medium value—by one productive and one moderately productive or by two moderately productive generations, and a low value—by one productive, or moderately productive, and low productive generations. In addition, overall mortality rates were calculated for generations with various productivity levels. The greatest variability of mortality rates was observed in immature walleye pollock; the maximum mortality rate was typical for the recruitment of highly abundant generations, and the minimum, for the least abundant ones. The lowest mortality was recorded at the age of mass maturation. Mature individuals of generations with various productivity levels showed insignificant differences in overall mortality rates.