NOTE Rom^n-Rodriguez and Hammann: Age and growth of Totoaba macdonaldi 
623 
200 
180 
160 
>N 
140 
o 
c 
120 
CD 
3 
100 
c r 
<D 
80 
LL 
60 
40 
20 
n = 1,125 juveniles + 157 adults 
Thn-n-n n- . 
■ nn-rl}fTTHlfh>^ , 
1“ C\J CO 
Standard length (mm) 
Figure 3 
Length-frequency distribution for totoaba specimens collected 
in the Gulf of California, n = 1,282. 
Figure 4 
Relation between otolith weight and totoaba standard length, n = 118. 
(378-620 mm SL), and one was of age class 3 
(740 mm SL). The remaining specimens were 
adults between age classes 4 and 24. The index 
of average percent error was 16.10% for the single 
reader. 
Observed lengths and otolith ring counts were 
used to fit the von Bertalanffy model to obtain 
the growth curve for the totoaba population in 
the Gulf of California (Fig. 7); the fit was good 
(r 2 =0.98, n = 101). Past ages (n = 346) were 
backcalculated from the thin-section otolith ra- 
dius (OR) to fish length relation of 81 fish, and 
the von Bertalanffy growth model was also de- 
termined (Fig. 7). Table 2 compares the observed 
standard lengths with those calculated from both 
growth models. Figure 8 shows the relation be- 
tween maximum whole otolith length and age as 
an exponential function. 
In the case of the fish that died after a year of 
captivity ( 11 mo 21 d), its otoliths showed only 
one ring; the second fish held for two years, 
had two rings. The otoliths from the third 
specimen were decalcified and readings, un- 
fortunately, were not possible. Fish held in 
captivity were captured in the same trawls 
as the rest of the juveniles used for age deter- 
mination in this study. Otoliths of juveniles sac- 
rificed at the time of capture did not present 
any rings or marks similar to those detected in 
otoliths of the individuals kept in captivity. 
Discussion 
The relation between otolith dimensions and 
fish length can be used to obtain data from 
the totoaba heads commonly found on the 
beaches of the northern Gulf. This relation 
is particularly important when one consid- 
ers the restrictions and the potential impact 
of sampling an endangered species. Otolith 
growth and fish growth are proportional re- 
gardless of how growth rate changes with time; in 
early stages, both fish and otoliths increase faster 
than in adult stages after maturity is reached. 
Barbieri et al. (1994) reported for Atlantic croaker 
( Micropogonias undulatus ) that age has an impor- 
tant effect on the otolith dimension to fish length 
relation. For totoaba, however, fish length alone de- 
scribed over 98% of the variability in otolith size. This 
growth pattern is common for other sciaenid species 
(Ross, 1988; Murphy and Taylor, 1989). 
The relation between standard length and otolith 
radius in sciaenids has been fitted to several growth 
equations. Maceina et al. (1987) and Blake and Blake 
(1981) found good fit with a linear model, but Barger 
(1985) found the best fit with a power function. For 
totoaba in our study, the best fit was found with a 
Gompertz model for radius along axis 1. The wide range 
of radii at the maximum fish length (shown in Fig. 6), 
supports our assumption that annuli are formed 
throughout the life of the fish, as is also suggested by 
the power function fitted to the otolith length and age 
relationship (shown in Fig. 8). Barbieri et al. (1994) 
also reported the formation of annuli throughout the 
life of the Atlantic croaker. Although the otolith length 
to age relation could be used to estimate fish age, the 
fit is not as good as that between standard length and 
