MacNair et al.: Age, growth, and mortality of Pciralichthys californicus 
597 
The data in our study confirmed that females grow fast- 
er than males, as found in previous studies (Pattison and 
McAllister, 1990; Sunada et al., 1990), and that growth was 
different between males and females for each region. Fe- 
males in both regions had larger asymptotic mean lengths, 
, than males (Table 9). 
Growth curves for males and females crossed between 
ages 1 and 2 for southern California and at age 3 for cen- 
tral California (Fig. 6). This finding suggests that young 
male and female halibut are of similar size until about ages 
2 and 3 in southern and central California, respectively. 
However, Haaker (1975) found that juvenile female hali- 
but in Anaheim Bay grew faster than males. The crossover 
in growth curves may be due to the small sample sizes for 
ages 1 and 2 in our study. The growth curves also involved 
some extrapolation for very young ages. 
Our study showed lower mean length-at-age than that 
obtained by Pattison and McAllister (1990); however, the 
differences for females were slight. These differences may 
partly be attributed to different environmental conditions 
in the years prior to each study. Pattison and McAllister 
used otoliths collected from 1955-66 and 1984-88, where- 
as we used otoliths collected from 1993 to 1995. Manooch 
and Potts (1997) in a study of greater amberjack in the 
Gulf of Mexico also cited temporal changes as one of 
the factors that may have contributed to differences in 
growth between greater amberjack in southern Florida 
and northern Gulf of Mexico. The geographic range of 
the samples may also have affected the results because 
we found growth differences between southern and cen- 
tral California. Pattison and McAllister’s study encom- 
passed samples from central and southern California, but 
they did not separate the two regions in their analysis. 
In addition, gear selectivity may have contributed to the 
differences found between our two studies. Pattison and 
McAllister used halibut that were collected with several 
gear types (trawl, gill net, beach seine, hook and line, and 
spear), whereas our study sampled halibut with only trawl 
gear of a specific mesh size. Potts et al. ( 1998) found while 
studying Vermillion snapper from the southeastern Unit- 
ed States that the different gear types used in sample col- 
lection may bias growth results. 
Sunada et al. (1990) found that for commercial halibut 
landings in southern California the asymptotic mean 
length, L^, was 909 mm TL for males and 1445 mm TL 
for females. In comparison, our study showed for southern 
Table 8 
Mann-Whitney comparisons of California halibut from 
southern and central California for mean length at age. 
Asterisk (*) indicates statistical significance. 
Age 
(yr) 
Mean observed 
total length (mm) 
Sample 
n 
size 
Mann- 
Whitney 
P-value 
Southern 
Central 
Southern 
Central 
Males 
2 
289.4 
325.9 
103 
15 
0.0001* 
3 
319.3 
384.8 
178 
46 
0.0001* 
4 
377.3 
447.8 
110 
26 
0.0001* 
5 
417.2 
492.8 
106 
9 
0.0006* 
6 
481.7 
538.6 
92 
20 
0.0002* 
7 
505.6 
595.6 
97 
13 
0.0002* 
8 
538.3 
582.5 
40 
13 
0.08 
9 
551.5 
648.7 
23 
3 
0.03* 
Females 
2 
291.9 
312.9 
21 
12 
0.10 
3 
364.4 
373.4 
42 
46 
0.92 
4 
462.6 
493.5 
54 
35 
0.21 
5 
520.5 
606.2 
58 
17 
0.002* 
6 
591.2 
672.0 
70 
4 
0.07 
7 
616.1 
725.5 
41 
2 
0.04* 
8 
666.0 
810.4 
26 
5 
0.01* 
9 
736.2 
842.0 
11 
5 
0.17 
California a slightly higher for males at 925 mm TL, 
and a lower L x for females at 1368 mm TL. The asymp- 
totic mean length for females may be lower because fewer 
large females were collected in our study. Although our 
study had different growth parameters than those of Su- 
nada et al. (1990), the differences were only slight. The 
differences may have been due to gear vulnerability. Su- 
nada et al. (1990) collected halibut from both trawl nets 
and gill nets and found that fewer females were collected 
in trawl nets, which may be attributed to trawl gear being 
restricted to offshore areas during spawning season. Also 
Table 9 
Von Bertalanffy growth parameters with asymptotic standard errors (SE) for California halibut by sex in southern and central 
California. Length is given in mm TL. 
Region 
Sex 
n 
u 
SE 
K 
SE 
*0 
SE 
Southern 
male 
761 
925.3 
121.4 
0.08 
0.02 
-2.2 
0.41 
female 
336 
1367.7 
273.4 
0.08 
0.03 
-1.2 
0.48 
Central 
male 
147 
956.7 
211.9 
0.10 
0.05 
-2.1 
0.91 
female 
129 
1477.1 
308.1 
0.10 
0.04 
-0.2 
0.43 
