13. Re-evaluating the Age Determination of Spiny Dogfish Using Oxytetracycline and Fish at Liberty up to 20 Years
Gordon A. McFarlane and Jackie R. King
Abstract.—Counts of annuli that form on the mantle of the second dorsal spine of 59 spiny dogfish Squalus acanthias that had been at liberty for up to 20 years after marking with oxytetracycline in most cases corresponded to the years at liberty (87% within 1 year). These results confirm the pattern of annual band formation on the second dorsal spine and validate its use in age estimation. We identified two potential sources of error when estimating the number of annuli on the spine: 1) inaccurate annuli counts near the base of the spine due to irregular enamel deposition and 2) inaccurate location of the no-wear point and subsequent inaccurate measurement of the spine diameter at the no-wear point, which affects estimation of missing annuli using the no-wear point algorithm. In addition, we confirm the validity of Ketchen’s (1975) no-wear point algorithm for the estimation of missing annuli on the worn portion of the distal tip of the spine.