Lopez-Rasgado and Herzka: Assessment of habitat quality for |uvenile Paralichthys califormcus 
347 
residuals were close to normally distributed (Shapiro 
Wilk’s statistic=0.984, P=0.031). 
Otolith growth rates of natural populations 
Using measurements of daily increment widths as a 
proxy for somatic growth rate, we relied on two assump- 
tions: 1) that growth increments in the form of ring 
formations in otoliths occurs daily, and 2) the increment 
widths of otoliths are proportional to somatic growth 
(i.e., there is a linear relationship between fish size and 
otolith size; Campana and Jones, 1992). Kramer (1991) 
and Kicklighter (1990) validated daily ring formation 
in larval and juvenile California halibut, respectively. 
Using caging experiments to evaluate otolith and somatic 
growth rates in juvenile California halibut, Kicklighter 
(1990) documented a strong linear relationship between 
SL and otolith length for juveniles ranging from 40 to 
100 mm SL. Kicklighter (1990) also reported a linear 
relationship between mean recent otolith growth (14 
days) and somatic growth (y=0.619x+0.093, r 2 = 0.55). 
Hence, the measurement of recent increment widths as 
a proxy for somatic growth rates in juvenile California 
halibut is justified. 
Wild-caught juveniles were placed over ice in indi- 
vidual bags and later frozen in the laboratory. We chose 
five individuals from each of the following size classes 
for otolith analysis: 50-80, 81-120 and 121-160 mm 
SL (n=15 per date and section of the estuary). Sagittal 
otoliths were extracted, cleaned in a sonicator with a 
10% bleach solution to remove tissue, rinsed with dis- 
tilled water, dried, and mounted on slides sulcus-side- 
down with Krazy Glue (Industrias Kola Loka SA de CV, 
Mexico State, Mexico). The right or left sagittal otolith 
was chosen randomly. The percent difference in length 
between the sagittal otoliths dissected from the eyed or 
blind side of both right and left-eyed juveniles is small 
(mean ±standard deviation [SD] in relation to blind 
side=-1.7% ±3.0%, range -11.1% to 2.5%, n=20). 
Polishing was necessary to reveal daily growth incre- 
ments in the otolith posterior margin. Polishing cloths 
of several sizes (34.3, 22.1, 14.5, and 6.5 pm) were used 
depending on otolith size and visibility of daily incre- 
ments. Otoliths were given a final polishing with a 
0.3-pm aluminum powder and soaked in 5% EDTA to 
increase the visibility of daily growth increments. 
We were interested in examining the relationship be- 
tween recent growth rate and environmental conditions 
over a relatively short time period to minimize the pos- 
sibility that individuals had moved substantially within 
the estuary. We measured the width of daily growth 
increments for the period corresponding to the 14 days 
before capture (corresponding to the second half of the 
caging experiment). Daily increments, consisting of an 
opaque and translucent ring, were viewed under 400 x 
magnification. The width of each increment was mea- 
sured parallel to the main growth axis of each otolith in 
the posterior margin (range of widths 3-15 pm; mean= 
6 pm ±2 SD) by using an imagine analysis system con- 
sisting of a compound microscope and digital camera 
connected to a computer loaded with Image J analysis 
software (National Institutes of Health, Bethesda, MD). 
We had difficulty distinguishing the interface between 
the opaque and translucent rings of the outermost in- 
crements with sufficient clarity to accurately measure 
the daily increment widths, although we could identify 
daily increments. We therefore counted the 14 incre- 
ments deposited before capture and measured the width 
of those in which the interface between the opaque 
and translucent rings was clear to obtain an accurate 
measurement. The number of increments measured in 
a given otolith ranged from 5 to 12 (mean = 9 ±3 SD). 
Otoliths for which we could not measure at least five 
increments were discarded (about 20%). In those cases, 
we prepared additional otoliths from fishes of the same 
size class. Each increment was measured three times 
and its average width was used in subsequent calcula- 
tions. Recent growth rates are reported in pm/day. 
The width of daily increments can vary as a function 
of fish size. Analysis of covariance (ANCOVA) has been 
used in previous studies to remove size-related differ- 
ences in tests for differences in otolith growth rates 
among groups (e.g., Phelan et al., 2000). We evaluated 
whether recent otolith growth was correlated with SL 
within the 50-160 mm SL size range that we examined. 
Data from fishes collected in different sections of the 
estuary at a given time were pooled. Sampling periods 
were considered separately and six correlations were 
performed (n - 45 fish per sampling period). Only one 
correlation was positive and significant (October 2004; 
P<0.001) and a second was slightly negative and mar- 
ginally significant (January 2005; P=0.032). In both 
cases, the proportion of the variance in recent otolith 
growth rates explained by SL was very low (^=0.26 and 
r 2 = 0.10, respectively). Hence, we did not find a strong 
dependence of recent otolith growth rates on size within 
our target size range. Recent otolith growth rates of 
natural populations were thus analyzed withg two-way 
ANOVA and by using time and section of the estuary 
as fixed factors. Data were log (x+1) transformed to 
comply with the assumption of normality. Tukey HSD 
tests were used to test for specific differences between 
means after ANOVA. 
We used correlation analysis to test the hypothesis 
that higher growth rates coincide with higher density of 
juveniles <200 mm SL and to examine the relationship 
between recent otolith growth rates of natural popula- 
tions and temperature. Mean temperature during the 14 
days before their capture was calculated by using data 
from thermographs deployed during caging experiments 
(see below). Correlation analysis was performed only for 
times and sections of the estuary for which both otolith 
and temperature data were available. 
Somatic and otolith growth rates of caged fishes 
Valle et al. (1999) examined the fine-scale distribution 
of juvenile California halibut in shallow (<1.1 m depth) 
waters of Alamitos Bay, CA, in relation to the presence 
or absence of eelgrass habitat. Juveniles were 2-6 times 
