HOHN and HAMMOND: POSTNATAL GROWTH OF SPOTTED DOLPHIN 



GLG (beginning with the neonatal Hne) is important 

 in estimates of age in young animals. For a specimen 

 estimated to be 0-yr-old based on GLGs but which 

 is known not to be a neonate, the age must neces- 

 sarily be an underestimate of the actual age of that 

 specimen, and, consequently, the average length of 

 "0-yr-olds" would be greater than the average length 

 of new-born specimens. When the Gompertz model 

 (with L„ not fixed) is fitted to the age data, the 

 predicted length at age is 89.6 cm, 4.2 cm higher 

 than the length-at-birth estimate The age at which 

 the predicted length is 89.6 cm when Lq is fixed at 

 85.4 cm is about 0.1 GLGs. This indicates a possible 

 bias of about 0.1 GLGs for young animals. However, 

 this difference between predicted length for fits of 

 the model with fixed and floated Lq diminishes 

 rapidly and at 0.7 GLGs predicted length is 114.0 

 cm for both models. 



The Gompertz model appears to be generally 

 suitable in describing the early growth of the off- 

 shore spotted dolphin based on GLG readings. 

 However, the pattern of points around the fitted line 

 in Figure 7 up to about 1.1 GLGs indicates that 

 growth during this period may not be adequately 

 described by a single curve This pattern may be a 

 result of either sampling variation or errors in 

 reading, but it may be due to changes in growth rate 

 during this period resulting from changes in food 

 intake Perrin et al. (1976) have estimated that wean- 

 ing occurs at about 11 mo in the offshore spotted 

 dolphin so that during the period from about 8 to 

 13 mo, milk intake will be decreasing and the intake 

 of solid food will be increasing. Growth rates may 

 well reflect these changes. If this is the case, a two- 

 cycle model may describe growth more accurately 

 during this period. Such an approach was used by 

 Perrin et al. (1976, 1977) in spotted and spinner 

 dolphins, respectively, to describe a secondary surge 

 in the growth of pre-adult animals. 



CONCLUDING REMARKS 



Our analyses have produced different estimates of 

 growth rates and lengths-at-age from two different 

 techniques. The reliability of fitting growth curves 

 to series of means of identifiable distributions of 

 length by month depends primarily upon being able 

 to select a sample in which breeding is both seasonal 

 and synchronous from year to year. The reliability 

 of fitting growth curves to length-age data as deter- 

 mined by counting GLGs depends primarily upon the 

 validity of the assumption that 1 GLG is equivalent 

 to 1 yr. We believe that neither technique is suffi- 

 ciently reliable to be labelled as the "best" method 



or to try to calibrate the other. Rather, our analyses 

 underline the need for the analysis of data collected 

 from known-age animals of these populations. 

 However, we do believe that the estimates of growth 

 rates and lengths-at-age presented here are the best 

 currently available for offshore spotted dolphins 

 from the eastern tropical Pacific 



ACKNOWLEDGMENTS 



Teeth were prepared by P. Sloan, M. Kimura, and 

 D. Stanley. Age determination readings were made 

 by A. Myrick and the first author. J. Barlow offered 

 advice on growth models and W. Perrin made sug- 

 gestions during the course of the analyses. Most of 

 the illustrations were prepared by R. Allen. R. 

 Hankins and S. Chivers were particularly helpful in 

 data editing, computer programming, and some data 

 analysis. We would like to thank R. Brownell, Jr., D. 

 Chapman, F. Hester, and D. Siniff and colleagues at 

 the SWFC and lATTC, especially J. Barlow, D. 

 DeMaster, A. Myrick, W. Perrin, M. Scott, and A. 

 Wild for critical reviews of an earlier version of the 

 manuscript. 



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 Best, R B. 



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

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