A Comparison of Three Anatomical Structures for Estimating Age in a Slow-Growing Subarctic Population of Lake Whitefish

Abstract

It has been well documented in previous research that otoliths are the preferred hard structure for estimating age in coregonids. However, the slower growth due to short growing seasons experienced by populations in the subarctic region of the boreal zone may alter the utility of alternative nonlethal structures for estimating age. We compared the three most commonly used age estimation structures (otoliths, pectoral fin rays, and scales) for Lake Whitefish Coregonus clupeaformis in a northern (above 50°N) population from Great Slave Lake. This study provides new perspectives regarding the use of different aging structures with fish populations typical of subarctic and arctic environments. Results of ANOVA showed that reader confidence, within-reader precision, and the age estimates themselves were all affected by age structure; reader confidence also varied with age-class. Reader confidence was highest for age estimates from otoliths, followed by pectoral fin rays and then scales. Similarly, within-reader precision (as measured by CVs) was highest for age estimates from otoliths, followed by scales and then pectoral fin ray sections. Pairwise comparisons between age estimates from otoliths and those from scales or pectoral fin rays indicated no significant differences when fish were younger than 10 years (scales) or 12 years (fin rays), suggesting that these nonlethal structures could be conservatively used to reliably estimate ages of younger (<10 years) and smaller (≤300 mm FL) Lake Whitefish. Of particular significance are the findings that (1) divergence between scale and otolith age estimates is delayed by 5–6 years relative to more southerly populations; and (2) in contrast to examples from southern populations, fin rays do not offer a suitable nonlethal alternative for estimating ages of older Lake Whitefish (>11 years).

Received March 4, 2014; accepted December 3, 2014

ACKNOWLEDGMENTS

We gratefully acknowledge the many people who helped with fish sample collections for this study, especially G. Low (Dehcho First Nations), S. Buckley (Hay River Metis Council), and D. Beaulieu, D. Lafferty, S. Biscaye, M. Edjericon, and S. Rymer (Deninu K'ue First Nations). We thank W. Irvine, A. Cook, and C. McDonald (OMNR) for assisting in preliminary analysis and sampling processing, and L. Vandenbyllaardt (DFO) for age estimation by reading otoliths. We also are grateful to J. Babaluk (retired DFO biologist) for his help in the method design and equipment selection for the otolith grind-and-bake technique. We greatly benefited from the information, logistic support, and text editing that were provided by C. Day, M. Treble, and M. Friesen (DFO). Critical reviews by three anonymous referees substantially improved the quality of the manuscript. This study was funded by the Northwest Territories Cumulative Impacts Monitoring Program and the DFO Aboriginal Fisheries Strategy.