MacNair et at: Age, growth, and mortality of Paralichthys californicus 
589 
Table 1 
Number of trawls and number of California halibut used in age and growth analyses by depth strata and region. Asterisk (*) 
indicates that these fish were not used in the mortality estimates because they were caught at a later date. 
Stratum 
Southern California 
Central California 
Depth (fm) 
No. of trawls 
No. of halibut used 
Area (nmi 2 ) 
No. of trawls 
No. of halibut used 
Area (nmi 2 ) 
1 
0-20 
58 
913 +3* 
575 
47 
254 
587 
2 
21-40 
46 
165 +2* 
495 
39 
22 
905 
3 
41-60 
45 
13 +1* 
425 
40 
0 
1124 
Total 
1091 +6* 
276 
deposited in winter (from November to March). A 
combination of an inner opaque and adjacent out- 
er translucent zone represents an annular growth 
ring or annulus (Casselman, 1983). This growth 
ring was validated by Pattison and McAllister 
(1990) with oxytetracycline-marked otoliths; they 
found that only one complete ring (opaque and 
translucent) was formed each year. 
Pattison and McAllister suggested that age es- 
timates of older fish (age 11 or older) may be 
underestimated when whole otoliths, rather than 
sectioned otoliths, are read. In the preliminary 
analysis in our study, to test if a significant dif- 
ference existed between estimating age with whole 
otoliths and estimating age with sectioned otoliths, 
an otolith from each of 80 randomly selected fish 
(10 fish from each 100-mm size class from 200 to 
900 mm TL) was viewed both whole and sectioned 
to estimate age. A mutually determined age (an age 
agreed upon by the two readers) was established 
for the whole otolith, as well as for the sectioned 
version of the otolith. If the age readings were 
identical for each reader, then that age was consid- 
ered the correct age. Otherwise, the two readers 
discussed the readings and agreed upon an age. The non- 
parametric, paired Wilcoxon test was applied to the pairs 
of whole and sectioned otolith ages for each fish. In addi- 
tion, a paired Wilcoxon test was applied to otoliths for fish 
restricted to 8 years and older (n=32). 
In addition to determining whether to use whole or sec- 
tioned otoliths, the preliminary analysis also involved de- 
termining how halibut age was to be estimated: either by 
using the mutually determined age, as already described, 
or an averaged age. The averaged age was a single value 
calculated as the mean of the four independent readings 
(whole or sectioned version of an otolith read by two read- 
ers on two different occasions) and rounded to the nearest 
integer. Sample means generally have the same type of 
sampling distribution as individual observations, but with 
a smaller variance. Hence, we applied the nonparametric 
paired Wilcoxon test to the pairs of averaged and mutually 
determined ages for each otolith (n= 80). The results from 
the preliminary analysis determined how we conducted the 
process of age determination in the main part of the study. 
We acknowledge that using sectioned otoliths is the rec- 
ommended procedure when analyzing long-lived fish. Al- 
though individual California halibut may live as long as 
30 years (Frey, 1971; Pattison and McAllister, 1990), all the 
fish in our study were relatively young (less than 14 years 
old). Because of our preliminary analysis and because sec- 
tioning a large number of otoliths (potentially over 1300) 
would have entailed considerable costs, all otoliths were 
initially read whole. We did use sectioned otoliths when the 
variability in the age readings for that otolith seemed to be 
unacceptably high and when the whole otolith was judged 
unreadable because of the anise oil residue. 
Before recording ages, two readers consulted with each 
other to standardize their technique for counting annuli. 
Each otolith was initially read whole, that is, the surface of 
the uncut otolith was read for the number of annuli pres- 
ent. The whole otolith was submerged in water, illuminat- 
ed with fiber optic light transmitted from the sides, and 
viewed against a dark background with a dissecting mi- 
croscope (16x to 25x). Figure 1 is an example of an otolith 
