14. Evaluation of the Precision of Age Estimates for Spiny Dogfish
Joel S. Rice, Vincent F. Gallucci, and Gordon H. Kruse
Abstract.—Effective management of dogfish fisheries requires knowledge of both their life history and population dynamics. Age data contribute to this knowledge and provide critical information for the estimation of stock–recruitment relationships, life-history parameters (e.g., mortality and growth rates), and lifetime reproductive potential. The estimation of age based on the second dorsal spine is subject to a variety of errors, including reader bias in the interpretation of which marks constitute annuli and how the structure is prepared. We estimated the precision of spiny dogfish Squalus acanthias ages by comparing age estimates made by four independent laboratories on a reference collection of 100 spines from spiny dogfish from Washington State waters. Personnel at each laboratory had been trained in the same manner and followed the same aging methodology. Age estimates were compared among laboratories and against the calculated median age estimation. Systematic differences in estimates of dogfish age among laboratories were found by graphical and statistical analysis. A coefficient of variation of 19% represents the overall precision of age readings for spiny dogfish based on this study. This level of precision was associated with statistically different laboratory-specific growth curves; however, this relative bias did not always result in a statistical difference between parameters derived from age–length relationships. Based on our results, an inter-laboratory study should be conducted to compare and resolve aging criteria before future, large-scale aging or population studies of dogfish are carried out.