Comparison of Eruption-Wear Patterns and Cementum Annuli as Age Criteria in Elk

An objective method for estimating the age of elk (Cervus canadensis) based on cementum annuli counts in stained sections of first incisor roots was developed. Ages estimated from cementum annuli structures agreed with the known ages of 18 elk used to check reliability of the technique. Eruption-wear age estimates by biologists working at elk check stations were compared to ages assessed from the dental cementum. Only 50 percent agreement was recorded between these two aging techniques when elk were placed in specific age groups. There is great need for a reliable elk-aging method employing a simple, easily applied technique for management use. Banfield (1949), Murie (1951), Swanson (1951), Quimby and Gaab (1952, 1957), and Hancock and Low (1956) have made contributions to this end, using the tooth eruption and wear method. The methods of Quimby and Gaab (1957), using the sequence of tooth succession and rate of wear on mandibular dentition, have been used widely for several years at big game check stations in Coloeat need for a reliable elk-age ploying a simple, easily apique for anagement use. Ban), urie (1951), Swanson (1951), rado. The information obtained has been relied upon to give age-class composition of elk harvests, and has been used in other management operations. It is now evident that there is variability in the results obtained by the eruption-wear techniques, due to different experience levels of biologists and to variations in tooth wear of individual animals as determined by environmental conditions. A technique of aging animals by examining nnular rings in the dental cementum has been reported by Scheffer (1950), who This content downloaded from 157.55. 39.223 on Wed, 24 Aug 2016 05:57:33 UTC All use subject to http://about.jstor. org/terms 176 Journal of Wildlife Management, Vol. 33, No. 1, January 1969 worked with Alaskan fur seals (Collarhinus ursinus), Laws (1952, 1953) for the elephant seal (Mirounga leonina), Sergeant and Pimlott (1959) for moose (Alces alces), McEwan (1963) for caribou (Rangifer tarandus), Mitchell (1963) for Scottish red deer (Cervus elaphus), Novakowski (1965) for bison (Bison bison), Ransom (1966) and Gilbert (1966) for white-tailed deer (Odocoileus virginianus), and more recently Erickson (1967) for mule deer (Odocoileus hemionus ). Cementum is deposited on the roots of the teeth, first on the dentine and then on itself, increasing the surface of the root as the deposition proceeds year after year. The rate of deposition changes with the seasons of the year, resulting in alternating dense-staining narrow, and light-staining wide bands. The wide band is presumably formed during the spring and summer, while the dark band is formed during the fall and winter. A pair of these alternating bands make up one annulus and the number of annuli are associated with the age of the animal in years. MATERIALS AND METHODS Erickson (1967) developed the rapid and efficient technique for sectioning teeth of mule deer, later applied to elk, used in this study. The process consists of drying first incisors and sawing them longitudinally with a thin-sectioning saw' into 95-micron sections, which are then demineralized and stained with IHarris' hematoxylin. This technique results in a tooth section which shows the major cementum annuli as narrow, darkstaining bands separated by broad, lightstaining bands. Preparatory to sawing, elk teeth were soaked overnight in uncatalyzed molding 1 Gillings-Brownwill Thin Sectioning Machine, Model No. 60, Brownwill Scientific, P.O. Box 277, Rochester, New York. resin. The resin was drained off and the teeth placed in plastic ice-cube trays, used as molds; catalyzed resin was poured over them to a depth of 10-15 mm and allowed to harden. The plastic-mounted teeth were sectioned by using the thin-sectioning saw; 3 sections, 95 microns thick, were sliced from each tooth starting at a point 3-5 mm from the apex of the root. The sections were placed on plastic tissue-processing capsules and demineralized by immersion into a 5-percent solution of formic acid for 15 minutes. The sections were rinsed with tap water and put into a saturated solution of lithium carbonate in 70-percent alcohol for 15 minutes to neutralize the remaining acid. Subsequently, the sections were rinsed in tap water and placed in Harris' hematoxylin for approximately 10 minutes. They were rinsed in tap water for 1 minute, followed by a 2-minute rinse in 35-percent ethanol. They were then decolorized in 0.5-percent sulfuric acid for approximately 20 seconds. The tooth sections could either be examined microscopically (lOOx) and the age estimation made immediately after the decolorization step, or the sections could be dehydrated and a permanent slide mount prepared. The latter was accomplished by placing the sections in 70-percent ethanol and 95-percent ethanol for 2 minutes each, followed by one change of absolute alcohol, one change of acetone, and two changes of xylene for 3 minutes each. The sections were permanently mounted on glass slides with synthetic resin. The preparation of permanent slides is time-consuming and requires a great deal of skill. It was found that for rapid, routine age determinations this part of the procedure was not necessary, and the tooth sections could be discarded after examination under the microscope. Eighteen known-age elk jaws were obThis content downloaded from 157.55. 39.223 on Wed, 24 Aug 2016 05:57:33 UTC All use subject to http://about.jstor. org/terms COMPARING ELK AGE BY TOOTH WEAR AND ANNULI * Keiss 177 tained from James H. Straley, Big Game Biologist, Wyoming Game and Fish Commission, Pinedale. The first incisors were removed, sectioned, stained, and the ages determined by the dental-cementum technique. Thirteen of the jaws were from animals tagged as calves during the first winter at 6-8 months of age. Five of the animals were tagged as yearlings during their second winter, as determined by spike antler. Most elk calves are born during late May or early June and the birthdate was assumed to be June 1 for age-determining purposes. Date of death was verified by individuals making kills during the regular hunting seasons. After procedures for aging elk by the dental-cementum method were developed, several experiments were designed to compare the accuracy of methods used by Colorado biologists based on eruption-wear techniques. Two-hundred elk jaws, collected over several years at big-game check stations, were assembled, numbered, and laid out on tables. A first incisor was removed from each jaw, and marked by number. An estimate of the age of the animal from which the jaw was taken was determined by the dental-cementum technique. Eleven biologists, of varying degrees of experience in elk aging by the eruption-wear technique, made age estimations for all jaws and recorded their results for comparison with estimation of ages by the dental-cementum method. An elk jaw board was available for use at all times, and a reprint of Quimby and Gaab (1957) was available for reference. During the big-game season for 1967, several study areas were established where biologists made age estimations of hunterkilled elk at check stations. These ages were recorded and a first permanent incisor was pulled with straight-beaked, upper anterior, tooth-extracting forceps (No. 1. standard). The tooth was placed in a numbered envelope and sent to the laboratory where it was processed for age estimation by the dental-cementum technique. RESULTS AND DISCUSSION Evaluations made in this study are confined mainly to age-classes considered as the time intervals into which specimens are segregated. Specimens became available from late September-November, so actual age is 4-6 months older than the designated year class. Yearlings are more nearly 11 years old; 2-year-olds are more nearly 21/2 years old; etc. Animals killed during the first fall are calves; second fall, yearlings; third fall, 2-year-olds; fourth fall, 3-yearolds; etc. In making age determinations from the transverse sections of first incisors the lingual-lateral quarter of the tooth usually has the thickest cementum layer, and annuli are more widely separated, making counting easier. One year must be added to the age estimate of the tooth since the permanent incisors do not erupt until late in the