852 
Fishery Bulletin 95(4), 1 997 
Table 2 
Comparison of size-at-age growth functions for three Kemp’s ridley sea turtle growth models. Age = known age for the Caillouet 
et al. (1995b) model, whereas age = skeletochronological age estimate for the Zug et al. (1997) model and the polyphasic model 
presented here. SCL = straight carapace length. 
Size-at-age estimate (cm SCL) 
Size-at-age estimate (cm SCL) 
Age 
(years) 
Caillouet et al. 
(1995b) 
Zug et al. 
(1997) 
This study 
(Fig. 2A) 
Age 
(years) 
Caillouet et al. 
(1995b) 
Zug et al. 
(1997) 
This study 
(Fig. 2 A) 
0 (hatchling) 
2.79 
8.86 
4.32 
13 
61.30 
59.49 
61.33 
1 
18.95 
14.85 
12.99 
14 
61.57 
61.63 
61.91 
2 
30.72 
20.39 
22.96 
15 
61.76 
63.62 
62.23 
3 
39.29 
25.50 
27.93 
16 
61.90 
65.45 
62.40 
4 
45.53 
30.23 
30.46 
17 
62.00 
67.14 
62.50 
5 
50.08 
34.60 
33.11 
18 
62.07 
68.70 
62.55 
6 
53.39 
38.63 
36.77 
19 
62.13 
70.15 
62.58 
7 
55.80 
42.36 
41.56 
20 
62.17 
71.48 
62.59 
8 
57.56 
45.81 
46.91 
21 
62.19 
72.72 
62.60 
9 
58.84 
48.99 
51.92 
22 
62.21 
73.86 
62.61 
10 
59.77 
51.94 
55.88 
23 
62.23 
74.91 
62.61 
11 
60.45 
54.65 
58.61 
24 
62.24 
75.89 
62.61 
12 
60.94 
57.17 
60.32 
25 
62.25 
76.79 
62.61 
development phase of any sea turtle species (see 
Chaloupka and Limpus, 1997; Chaloupka and 
Musick, 1997). 
On the other hand, the monophasic form of the 
Gompertz growth function used by Caillouet et al., 
(1986) in a single cohort growth study (weight gain) 
of 10 Kemp’s ridley sea turtles held in captivity 
clearly fitted the data well at least for the observed 
range (ca. 2-7 years old). In the Gompertz function, 
a nonmonotonic growth-rate function is assumed 
with a growth spurt in early development similar to 
the first growth spurt in our study (see Fig. 2B). 
Whether growth in Caillouet et al.’s (1986) study 
might have been better fitted by using a polyphasic 
Age (years) 
o 5 10 15 20 
Age (years) 
Figure 2 
(A) Kemp’s ridley sea turtle size (SCL cm) plotted as a function of the correction-factor age estimates derived 
from Zug et al. (1997). Solid curve shows the polyphasic logistic growth Equation 1 fitted to the growth data 
shown in Figure 1A, excluding the single outlier. (B) The age-specific growth-rate function for the Kemp’s ridley 
sea turtle growth function shown in Panel A represented by the first derivative of Equation 1, which isy' w = X (O', P, 
(sech 2 (P, (t - 5 ; )))) with the same parameters defined for Equation 1 and with sech (hyperbolic secant) = (1 - tanh). 
