620 
Age and growth of totoaba, 
Totoaba macdonaldi (Sciaenidae), 
in the upper Gulf of California 
Martha J. Roman Rodriguez 
Instituto del Medio Ambientey el Desarrollo Sustentable del Estado de Sonora (IMADES) 
Reyes y Aguascalientes esq. Col. San Benito. C.P 83190, Hermosillo, Sonora, Mexico 
M. Gregory Hammann* 
Centro de Investigacion Cientlfica y Educacion Superior de Ensenada (CICESE) 
Dept, of Ecology, Fisheries Ecology Group 
Km. 107 Carr. Tij.-Ens. Ensenada, Baja California, Mexico 
E-mail address: ghammann@cicese.mx 
The totoaba, Totoaba macdonaldi 
(Gilbert), also known as Mexican 
giant bass, is found only in the Gulf 
of California. This species during 
1934-45 supported one of the most 
important sport and commercial 
fisheries in the Gulf, with total an- 
nual landings exceeding 2,000 met- 
ric tons (Rosales-Juarez and Ra- 
rmrez-Gonzalez * 1 ). At present, it is 
considered endangered (Flanagan 
and Hendrickson, 1976; NMFS 2 ) as 
a result of 1) a high mortality of ju- 
veniles in shrimp trawl nets, 2) past 
overexploitation, 3) current illegal 
fishing during its reproductive sea- 
son (early February to early May), 
and 4) ecological alterations of its 
spawning and nursery grounds. 
Flanagan and Hendrickson (1976) 
suggested that there was a high 
probability that this species would 
become extinct by 2000 AD. In 1975 
the Mexican government declared 
a moratorium on fishing totoaba. 
This paper reports on the age and 
growth of totoaba as determined 
from sectioned-otolith readings and 
contrasts current population age 
composition with what was known 
about the early population. Previ- 
ous studies have reported ages 
based on nonvalidated scale read- 
ings (Nakashima, 1916; Berdegue, 
1955; Molina et al. 3 ). 
Materials and methods 
Totoaba were sampled in 1986-91 
from the northern part of the up- 
per Gulf of California between 31° 
and 32° N Lat. and 114° and 115° 
W Long. (Fig. 1). In 1989-91, juve- 
niles were collected from shrimp 
trawl nets. Adults were sampled 
with gill nets during their repro- 
ductive season (Feb-Apr) of 1986, 
1987, and 1989-91. 
After determining individual 
standard (SL) and total length (TL) 
in millimeters and weight in grams, 
we extracted otolith (sagittal) pairs 
from 118 fish and embedded them 
in epoxy resin. For comparison with 
other age studies of totoaba, a lin- 
ear regression was performed for 
converting total length into stan- 
dard length. Lowerre-Barbieri et al. 
(1994) reported that sectioned 
otoliths were the best structure for 
ageing weakfish, Cynoscion regalis. 
To permit data recovery when 
only severed heads were available, 
118 otoliths were weighed (OW; +/— 
0.001 g) and measured to determine 
their relation with SL (Pauly, 1984); 
only whole individuals were used 
in the present study. Maximum 
otolith length (OL; +/- 0.05 mm) 
was measured from rostrum to 
postrostrum margins (anterior- 
posterior), and maximum otolith 
thickness (OT; +/- 0.05 mm) from 
the dorsal to ventral margins (dis- 
tal-proximal plane). 
A transverse section was made 
from 101 otoliths with an Isomet 
low speed saw following a tech- 
nique described by Beckman et al. 
(1990), Lowerre-Barbieri et al. 
(1994), and Secor et al. 4 and the 
otolith ring counts were read to 
determine age. Each thin section 
was read three times with trans- 
mitted light in a bright field by the 
same person. Following the crite- 
ria of Beamish and Fournier (1981), 
we calculated an index of average 
percent error for the single reader. 
Three different axes (Fig. 2) were 
explored to measure the otolith ra- 
dius (OR) of 94 thin sections. An- 
nuli were most clearly counted and 
measured along axis 1; thus otolith 
radius (OR) was defined as the dis- 
tance from the center of the core to 
the otolith outer edge along the ven- 
* Author to whom correspondence should be 
sent. 
1 Rosales-Juarez, F., and E. Ramirez- 
Gonzalez. 1987. Estado Actual del 
Conocimiento Sobre la Totoaba (Cynoscion 
macdonaldi), Gilbert 1890. Secretaria 
de Pesca, Mexico, 41 p. ISBN 968-817-086- 
0. [In Spanish; available at CICESE 
library.] 
2 NMFS (National Marine Fisheries Ser- 
vice). 1991. Endangered Species Act 
Status Review, totoaba ( Cynoscion mac- 
donaldi). Prot. Spec. Manage. Admin. 
Rep. SWR-91-01, 9 p. 
3 Molina, D., M A. Cisneros-Mata, R. Urias, 
C. Cervantes y M. A. Marquez. 1988. 
Prospeccion y evaluacion de la totoaba 
( Totoaba macdonaldi) en el Golfo de 
California. Tech. Report, 18 p. [In Span- 
ish, available from Cisneros-Mata, CRIP- 
Guaymas, Calle 20, No. 605 Sur, Guay- 
mas, Sonora, Mexico c.p. 85400.] 
4 Secor, D. H., J. M. Dean, and E. H 
Laban. 1990. Manual for otolith re- 
moval and preparation for microstructural 
examination. Electric Power Research 
Inst., The Belle W. Baruch Inst, for Ma- 
rine Biology and Coastal Research, 85 p. 
Manuscript accepted 27 February 1997. 
Fishery Bulletin 95:620-628 ( 1997). 
