Rocha-Olivares: Age, growth, and mortality of Lutjanus peru 
563 
species, including systematic underestimations 
(e.g. Bilton, 1973; O’Gorman et al., 1987; see 
review by Beamish and McFarlane, 1987, and 
papers therein). 
Because of the lack of reliable information on 
biological parameters for this commercially 
important tropical species, this work represents 
the first comprehensive study of growth and 
mortality of a L. peru population based on 
otolith age determinations. A comparison of age 
estimates from whole and sectioned otoliths and 
from scales is made to assess their relative use- 
fulness. Growth and mortality rates are esti- 
mated, and other aspects of the biology are pre- 
sented for an exploited population of the Pa- 
cific red snapper off the southeast coast of Baja 
California Sur. 
Materials and methods 
Study area and sampling scheme 
This study took place in Bahia de La Paz, one 
of two major bays in the Gulf of California 
{Walker, 1960). The most important fishing 
grounds for L. peru lie within and southeast of 
the Bay, around Espiritu Santo-Partida and 
Cerralvo Islands (Fig. 1). Peak catches occur 
during the summer. 
Pacific red snapper were collected from March 
1989 to March 1991. Most samples came from La 
Paz City fish market, which was sampled at least 
weekly, March 1989 to February 1991. Snappers were 
also collected monthly with baited hook and line, May 
1989 to February 1991. Juvenile red snappers were 
collected as shrimp trawler bycatch during Febru- 
ary and March 1991. Biological samples were taken 
from all fish collected (n=2605). In the market, sam- 
pling time was limited to the period before fish were 
stored, therefore biological sampling was restricted 
to the first 20 randomly selected individuals from 
each 4-cm length interval. Biological samples con- 
sisted of both sagittae, at least 10 scales from under- 
neath the left pectoral fin, and testes and ovaries, 
which were fixed in 10% buffered formalin and used 
for sex determination and reproduction studies. To- 
tal and standard lengths (TL and SL, respectively) 
were measured to the nearest mm; total and gutted 
weights (TW and GW, respectively) were recorded to 
the nearest 2 or 5 g, depending on fish size. Since 
fish were gutted on landing, some data and samples 
could not be obtained from the market. However, 
many gutted fishes could be sexed from gonadal re- 
mains. In 1989, when samples were most abundant, 
Figure 1 
Map of study area showing approximate positions (•) of fishing 
grounds and sampling sites of Pacific red snapper Lutjanus peru. 
Depth contours are in fathoms. 
3085 additional fishes were measured to construct 
sex-specific length-frequency distributions. 
Sample processing and age determination 
Because the left and right sagittae did not differ 
morphometrically 2 or in weight (paired f-tests, P>0.5) 
in a random subsample of 50 fishes representative 
of the length range available and since no differences 
were found in their marking pattern or number of 
rings, the right otolith was used for age determina- 
tion when available. Otoliths were submerged in 90% 
glycerol for 24 hours before they were viewed under 
a dissecting scope with reflected light over a dark- 
ened background. Otoliths embedded in thermoplas- 
tic cement were sectioned with a low-speed saw. 
Three sections (0.3 mm thick), including the primor- 
dium and the flanking regions, were made orthogo- 
nal to the anteroposterior axis of the structure. Sec- 
tions were glued to glass slides with cyanoacrylate- 
based cement and prepared for observation as de- 
2 Measurements compared are those described in Rocha Olivares 
and Gomez Munoz (1993). 
