Age determination of northeast Arctic cod otoliths through 50 years of history
Zuykova, N.V.; Koloskova, V.P.; Mjanger, H.; Nedreaas, K.H.; Senneset, H.; Yaragina, N.A.; Aanes, S.; Ågotnes, P. (2009). Age determination of northeast Arctic cod otoliths through 50 years of history. Mar. Biol. Res. 5(1): 66-74. http://dx.doi.org/10.1080/17451000802454874
In: Marine Biology Research. Taylor & Francis: Oslo; Basingstoke. ISSN 1745-1000; e-ISSN 1745-1019, meer
Norwegian and Russian Marine Research Institutes have investigated the possibility that biases in age determination from otoliths may have contributed to the long-term trends observed in the Northeast Arctic cod stock productivity: changes in growth, maturation rate, fecundity, etc. To determine the effects of changes in age reading protocols between contemporary and historical practices, randomly chosen material from each decade for the period 1940-1980s was re-read by experts. The quality of old otoliths stored in paper bags for more than 50 years was also assessed. Although some year-specific differences in age determination were seen between historical and contemporary readers, there was no significant effect on length at age for the historical time period. A small systematic bias in the number spawning zones detection was observed, demonstrating that the age at first maturation in the historic material as determined by the contemporary readers is younger than that determined by historical readers. The difference was the largest in the first sampled years constituting being approximately -0.6 years in 1947 and 1957. Then it decreased with time and was found to be within the range of -0.28-0 years in the 1970-1980s. The study shows that cod otoliths could be used for age and growth studies even after long storage.
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