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ICES Journal of Marine Science: Journal du Conseil 2006 63(8):1520-1529; doi:10.1016/j.icesjms.2006.06.002
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© 2006 International Council for the Exploration of the Sea

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

Craig R. Kastelle* and Daniel K. Kimura

National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Alaska Fisheries Science Center, Resource Ecology and Fisheries Management 7600 Sand Point Way N.E., Seattle, WA 98115-6349, USA

*Correspondence to C. R. Kastelle: tel: +1 206 526 4266; fax: +1 206 526 6723. e-mail: craig.kastelle{at}noaa.gov.

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.

Keywords: age determination, age validation, Pb-210/Ra-226, radiometric ageing, walleye pollock

Received 25 July 2005; accepted 5 June 2006.


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