CALIBRATION OF DENTAL LAYERS IN SEVEN CAPTIVE 



HAWAIIAN SPINNER DOLPHINS, STENELLA LONGIROSTRIS, 



BASED ON TETRACYCLINE LABELING 



Albert C. Myrick, Jr., 1 Edward W. Shallenberger, 2 

 Ingrid Rang, 2 and David B. Mac-Kay' 



ABSTRACT 



To calibrate dentinal and cemental growth layer groups (GLGs) with real time, a study was conducted on the 

 teeth from seven captive Hawaiian spinner dolphins that had been treated clinically with tetracycline (TCL) 

 at numerous times over multiple years at Sea Life Park, Hawaii. To monitor layer accumulation as it occurred 

 for 1 year, we gave single injections to three animals every 3 months and pulled a tooth from each every 6 months. 

 By comparing dental-layer patterns between TCL labels that had been introduced at 6-month and 1-year 

 intervals, annual patterns were distinguished. In the dentine, a thin, light layer (the first being the neonatal 

 line) was formed about every 6 months. Each annual GLG contained 13 lunar monthly layers (LMLs). Using 

 LML or light-layer counts, age, month, and year of birth were estimated for each of the seven specimens. All 

 seven deposited nearly the same dentinal GLG thickness in the same year of life. Estimates of birth months 

 indicated that five of the animals were born in late summer or early autumn and two were born in spring. Com- 

 parisons of dentinal labels with clinical records for a captive-born animal showed that TCL given to its 

 mother was imparted via milk to the nursing calf. Time calibration of cemental GLGs showed that usually one 

 cemental GLG was deposited annually, but in some cases a GLG was formed every second year or twice 

 a vear. 



The technique of "reading" layers or growth layer 

 groups (GLGs, terminology of Perrin and Myrick 

 1980) in teeth, developed to determine ages for pin- 

 nipeds in the early 1950's by Scheffer (1950) and 

 Laws ( 1952), is now used routinely in dolphin studies 

 (see reviews by Klevezal' and Kleinenberg 1967; 

 Jonsgard 1969; Scheffer and Myrick 1980). Early 

 work on dolphins (e.g., Nishiwaki and Yagi 1953; 

 Sergeant 1959), showing a correlation between 

 apparent age and number of GLGs led to the working 

 assumption that GLG-deposition cycles are con- 

 stant, each GLG usually, but not always, interpreted 

 as representing 1 yr. Critical analysis of this assump- 

 tion has been impaired by a lack of suitable 

 material. 



Three approaches have been used in efforts to 

 calibrate dental GLGs with time and to determine 

 their deposition rate: 1) In vivo labeling of tooth 

 layers, 2) multiple extractions of teeth over time, and 

 3) examination of teeth from animals of known age. 

 Nishiwaki and Yagi (1953) labeled the layered den- 

 tine in four wild-caught striped dolphins, Stenella 

 coeruleoalbo, by intramuscular injection of lead ace- 

 tate paste. None of the four survived long enough for 

 the labels to provide useful data. 



'Southwest Fisheries Center, National Marine Fisheries Service, 

 NOAA, La Jolla, CA 92038. 

 2 Sea Life Park, Makapuu Point, Waimanalo, HI 96795. 

 'Kaneohe Veterinary Clinic, Kaneohe, HI 96744. 



Nielsen (1972) treated a young wild-caught harbor 

 porpoise, Phocoena phocoena, with tetracycline 

 (TCL) three times over a 370-d period. Three 

 fluorescent labels were found in thin sections of its 

 teeth examined in ultraviolet (UV) light "... but the 

 uniform [unlayered] dentine made it impossible to 

 determine the number of growth-layers formed per 

 year" (Nielsen 1972:72). 



Best (1976) administered oral doses of TCL hy- 

 drochloride, "Mysteclin-V", on each day over an 8-d 

 period to each of three wild-caught dusky dolphins, 

 Lagenorhynchus obscurus. Labels were detected in 

 teeth of two of the three specimens after their deaths. 

 In one specimen, dentine accumulated for 703 d be- 

 tween treatment and death averaged 200 jum/yr and 

 0.56 jum/d. In the other (older) specimen, the average 

 deposition rate in dentine between the treatment 

 label and the pulp-cavity wall was 77 jiim/yr and 0.21 

 ftm/d. Best concluded that the thickness of GLGs 

 decreases significantly with age in dusky dolphins. 



Gurevich et al. (1980) successfully introduced a 

 single TCL label into the teeth of three of four wild- 

 caught adult common dolphins, Delphinus delphis. 

 The three labeled animals died 328, 354, and 441 d, 

 respectively, after the date of treatment. By estimat- 

 ing the dentinal pattern laid down in about 1 yr, the 

 investigators characterized an annual GLG. They 

 estimated the ages of the animals by assuming that 

 the GLGs in the unlabeled regions of the teeth rep- 



Manuscript accepted August 1983. 

 FISHERY BULLETIN: VOL. 82, No. 1, 1984. 



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