Dynamics of body size, age, and annual growth rate of Anadyr chum salmon Oncorhynchus keta in 1962–2010

Abstract

Interannual variability of body length, body weight, age structure, and seasonal growth rate of Anadyr chum salmon Oncorhynchus keta was studied using the monitoring data obtained in 1962–2010 in Anadyr River and Anadyr Firth. Body size of spawning adults has decreased significantly for the decade of 1990–2000s compared to the period of 1960–1970s, and the ratio of elder specimens was higher. Annual growth dynamics showed different patterns. Estimated from measuring intersclerite distances on scales, first-year growth of Anadyr chum salmon samples collected in 1962 to 2007 was enhanced. After the first year, growth was reduced. The greatest reduction occurred in the third and forth years. Analysis of seasonal growth of scale evidences to the relaxation of the growth rates of Anadyr chum salmon after the first year of life preconditioned by both the over-wintering and foraging period. These data are in contradiction with the wide-spread suggestion of decreasing of chum salmon body length during winter due to bad feeding conditions. According to the similarity of the dynamics of body length and growth rates of chum salmon and pink salmon O. gorbuscha observed for the last decades, we assume that this may be preconditioned by the same large-scale limiting factors that affect similarly these salmon species inhabiting vast areas. Our data do not support the idea about high-density population of chum salmon as a main factor affecting the productivity characteristics of this species in the northern Pacific Ocean in the second half of the 20th-beginning of the 21st century. Reasons for decrease of chum salmon body length are discussed.