Validation of Age Estimation in the Harp Seal, Phoca groenlandica, Using Dentinal Annuli

Abstract

1983. Validation of age estimation in the harp seal, Phoca groenbandica, using dentinal annuli. Can. J . Fish. Aquat. Sci. 40: 1430-1441. We investigated the validity and accuracy of age estimation in harp seals, Phoca grosra1~ndic.a~ using a sample of 155 known-age teeth from seals age 3 mo to 10 yr. Under transmitted light, transverse sections of harp seal canine teeth showed distinct incremental growth layers (IGLs) in the dentine. The first growth-layer group (GLG). representing1st-year growth, consists of two IGLs: an outer layer sf opaque dentine, bounded by the neonatal Iine, and an inner layer of translucent dentine. Subsequent GLGs. each representing 1 yr of growtla, generally consist of three IGLs: an outer layer of interglobular dentine deposited during the annual molt in April, a middle layer of opaque dentine formed during the northward spring migration (May-June), and an inner layer of translucent dentine formed from July to March. We show that dentinal GLGs can be used to estimate the absolute age of harp seals. The accuracy of the method decreases with age. Only 72.4q0 of estimates of 0-group seals were correct basing only transverse sections. These errors were virtually eliminated (489.0% ~O P P B :~~ age determination) when the tooth root was examined. Based on a single examination of a transverse section, the probabilities of correctly estimating age are 0.983, 0.889, 0.817, and 0.553 at ages I. 2, 3, and 4 + yr, respectively, when clearly inaccurate tag-tooth associations are omitted. The respective probabilities are only slightly higher when age is based on the average of five blind readings, k i n g 1.0, 0.889, 0.833, and 0.625. Beyond age 3 yr, existing data are insufficient to estimate reliably the accuracy of age determined by counting GLGs.

Comparative Feeding of Grey (Halichoerus grypus)and Common Seals (Phoca vitulina) in Coastal Waters of Iceland, with a Note on the Diet of Hooded (Cystophora cristata) and Harp Seals (Phoca groenlandica)

“…The ages of animals were determined by counting the number of growth-layers in the cementum, or alternatively, the dentine of harp seals were studied from thin-sections (0.5-0.7 mm) of the canine tooth, cut transverse with a low speed saw near the base of the tooth. A binocular dissecting microscope with 6 × to 50 × magnification and transmitted light was used (Bowen et al, 1983;Laws 1962;Lawson et al, 1992;Mansfield and Fisher, 1960).…”

Feeding habits of harp and hooded seals in drift ice waters along the east coast of Greenland in summer and winter

“…Sections were examined under transmitted light and ages estimated from counts of growth layers in the cementum for hooded seals (Born 1982) and the dentine for harp seals (Bowen et al 1983). …”

Growth and seasonal fluctuations in size and condition of male Northwest Atlantic harp seals Phoca groenlandica: an analysis using sequential growth curves

“…Core mass (M c ) was calculated as the difference between M t and M s . Age was determined by counting dentinal annuli from a cross-section of a lower canine tooth (Bowen et al 1983) and assuming seals were born on March 7 (Myers & Bowen 1989).…”