FISHERY BULLETIN: VOL. 82, NO. 1 



failed to produce distinct labels, none showed 

 evidence of cessation of dentine deposition. 



All cemental GLG counts corresponded in number 

 to dentinal annual GLG counts except in the case of 

 specimen WFP 670, where some regions of the 

 cementum showed double the number, and in 

 specimen ACM 104, where in some places the 

 cemental count was half that of the dentine. The find- 

 ing that in some cases cemental GLGs may form at 

 half or twice the rate of dentinal GLG deposition 

 points up the problem of using cemental GLGs to 

 estimate ages without reference to the dentine 

 (Myricket al. 1983). 



Evidence for an Internal Clock 



In the dentine of the animals studied, a thin GLG 

 boundary layer, beginning with the neonatal line, was 

 formed in the month of birth and on anniversaries of 

 the month of birth. Mid-GLG layers were formed 

 about 6 mo after formation of boundary layers. 

 Where LMLs could be calibrated, one was found to 

 form about every (lunar) month with high uniformity 

 in relative spacing. Such a cycle of deposition is 

 indicative of an internal clock, or clocks. The pattern 

 commences at birth and apparently is reset with solar 

 and/or lunar regularity without perceptible altera- 

 tion by fluctuation in the dolphins' natural or captive 

 environment or in calendric season of birth. That it 

 may not be a totally free-running system, i.e., not 

 without external cues, is suggested by the precisely 

 synchorized deposition of the fine and coarse pat- 

 terns of the dentine repeated over many years. 



Age at Sexual Maturity 



Perrin et al. (1977) indicated that sexual maturity 

 may be reached in females of Stenella longirostris at 

 an average 5.5 yr (range of 5-9 yr) and the average 

 period of gestation may be about 1 1 mo. From the 

 study of dentinal GLGs and TCL labels of specimen 

 ACM 104, it was possible to determine that this 

 animal was about 8-yr-old when she gave birth to her 

 calf. Assuming an 11 -mo gestation, we estimate that 

 she would have been 7-yr-old when she conceived. It 

 is not known whether the pregnancy resulted from 

 fertilization at her first or subsequent ovulations. 

 ACM 104 remains alive. This precludes examination 

 of her ovaries for ovulation scars. 



Reproductive Seasonality 



Based on the birth records of specimen WFP 670 

 and the calf of ACM 104 and the deductions made 



from dentinal layers, six animals were born in late 

 summer/early fall, and two were born in March. Since 

 all animals in the study represented the same popula- 

 tion off Kona, Hawaii, the early-spring and early-fall 

 birth patterns might indicate a corresponding two- 

 cycle pattern of reproductive peaks for the wild pop- 

 ulation generally. Such a seasonal pattern has been 

 suggested by Norris and Dohl (1980, fig. 16), but 

 Wells (in press), who has studied the population in 

 considerable detail, concluded that the breeding 

 season occurs from spring to fall, with most births in 

 the fall. Our sample was too small to verify Wells' 

 findings. 



Tetracycline Exposure to the Calf 

 Through the Milk 



The first two labels found in the dentine of 

 specimen WFP 670, the captive-born animal, were 

 interpreted as having been introduced through milk 

 received by the calf while the mother was being 

 treated with TCL. This recommends a possible prac- 

 tical application in indirectly treating newborns in ill 

 health. Excessive handling of such animals fre- 

 quently results in a worsening of their condition, 

 making the treatment more dangerous than the 

 malady. (Nursing calves not on solid food cannot be 

 treated with TCL-dosed fish and must be force-fed 

 or injected with drugs.) Separating the young calf 

 from its mother may produce additional com- 

 plications. 9 If treatments for the calf could be 

 administered through the milk by treating the mother 

 with TCL-dosed food, it seems likely that most of the 

 problem could be minimized. The question invites 

 further study. 



ACKNOWLEDGMENTS 



We thank D. G. Chapman, R. L. Brownell, Jr., D. B. 

 Siniff, A. Wild, W. F. Perrin, F. Hester, A. Dizon, and 

 J. Barlow for their critical reviews of the manuscript. 

 K. Raymond and R. Allen prepared the figures. M. 

 DeWitt typed the manuscript. 



LITERATURE CITED 



Best, P. B 



1976. Tetracycline marking and the rate of growth layer for- 

 mation in the teeth of a dolphin (Lagenorhynchus 

 obscurus). S. Afr. J. Sci. 72:216-218. 

 Gurevich, V. S., B. S. Stewart, and L. H. Cornell. 



1980. The use of tetracycline in age determination of com- 



9 L. H. Cornell, Sea World, Inc., San Diego, Calif., pers. commun. 

 1980. 



224 



