Age validation of walleye pollock (Theragra chalcogramma) from the Gulf of Alaska using the disequilibrium of Pb-210 and Ra-226

• Published in: ICES Journal of Marine Science
• Main Authors: Kastelle, Craig R., Kimura, Daniel K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2006
• Subjects: Ecology; Aquatic Science; Ecology, Evolution, Behavior and Systematics; Oceanography; Theragra chalcogramma; Alaska
• Online Access: http://dx.doi.org/10.1016/j.icesjms.2006.06.002; http://academic.oup.com/icesjms/article-pdf/63/8/1520/29126155/63-8-1520.pdf

Abstract The walleye pollock (Theragra chalcogramma) is a commercially important species in the North Pacific, and harvest quotas are dependent upon accurate determination of ages. The two techniques (called methods A and B) currently used to interpret the growth zone patterns in walleye pollock otoliths were compared. The age distributions from these two techniques differed; method B produced ages twice that of method A. Validation of ages from walleye pollock has not been done previously. Radiometric ageing based on the ratio of Pb-210/Ra-226 was used to evaluate the accuracy of otolith growth zone counts, and it demonstrated that method A, which produced younger ages between 3 and 8 years, was correct. Walleye pollock grow older than the 3–8 year (method A) age range validated in this study. The experimental design was limited to a maximum method A age of 8 years, because available samples did not provide the minimum of 40 fish required for estimating a radiometric age. Our radiometric ageing study on walleye pollock appears to be the first to use the Pb-210/Ra-226 radiometric age-validation method in a boreal fish species where all samples were potentially young, 8 years or less. In previous studies, radiometric ages often approached 100 years. Also, only one presumed year class was used, which was sampled in successive years. Therefore, Ra-226 sample measurements were averaged to provide lower error.