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Fishery Bulletin 107(3) 
ber 2005) did not coincide with a high proportion of 
empty stomachs. However, our study was not designed 
to directly relate recent otolith growth with feeding. 
Gut fullness levels are only a crude point-estimate of 
feeding success. Our recent otolith growth estimates 
represent the average daily growth over a 14 day pe- 
riod, whereas the time required to process ingested 
food is substantially shorter (1-2 days). Detailed stud- 
ies of food availability and consumption rates (e.g., 
Sogard, 1992) are necessary to identify the factors 
underlying variation in otolith growth rates of juve- 
nile California halibut. 
Density dependent processes, such as competition for 
food or space and predation pressure, can also influ- 
ence growth rates. We found a weak positive relation- 
ship between density and recent otolith growth rates 
of wild-caught juveniles, but the correlation was not 
significant (see also Fodrie and Levin, 2008). Hence, 
we did not find strong evidence to suggest limita- 
tion for food or space (negative density dependence) 
or the active selection of habitats supporting to higher 
growth rates (positive density dependence; Sogard, 
1992). However, density-dependent growth regula- 
tion may occur at smaller spatial scales than those 
examined in this study, and cannot be conclusively 
ruled out. 
Somatic and otolith growth rates of caged fishes 
Due to the low growth rates of caged juveniles, we 
could not use our recent somatic and otolith growth 
measurements as proxies for habitat quality. Most caged 
juveniles had empty stomachs. This could be due to a 
variety of factors, including limited availability of prey 
within the cages, limited feeding success and foraging 
ability, competition for food resources due to high fish 
density, or as a result of a stress response in relation 
to handling (e.g., Guindon and Miller, 1995). A density 
of 6 fish/m 2 is much higher than densities of juvenile 
California halibut found within embayments (Fodrie 
and Mendoza, 2006). 
During the first 14 days of caging, somatic growth 
rates of caged juveniles were very low (G = 0.0003 
to 0.0015 1/d). For fish 50 and 160 mm SL, this is 
equivalent to 0.01 to 0.12 mm/d, respectively, which 
is much lower than has been reported previously for 
wild-caught juveniles California halibut (0.13-1 mm/d, 
Haaker, 1975; Allen, 1988; Kramer, 1990; Kicklighter, 
1990). Accordingly, recent otolith growth rates of caged 
juveniles were also three to six times lower than in 
wild-caught juveniles (equivalent to 0.89-1.63 pm/d, 
mean=1.32 pm/d). Kicklighter (1990) also found very 
low otolith growth rates during his caging experi- 
ments; daily increment widths along the main growth 
axis were 0.49 to 2.26 pm. Fodrie and Herzka (2008) 
also reported limited otolith growth in some juveniles 
held in cages in Punta Banda Estuary. 
Somatic and otolith growth rates calculated over the 
28 days caging period were substantially lower than 
over the first 14 days, implying little or no growth 
during the second half of the experiment. The signifi- 
cant positive relationship between somatic and otolith 
growth during first 14 days indicates marginal incre- 
ment widths are reliable proxies for somatic growth 
at low growth rates, at least for a few days. However, 
uncoupling between otolith and somatic growth rates 
occurred during the second half of the experiment; 
there was virtually no difference in marginal incre- 
ment widths between fish retrieved after 14 and 28 
days. As discussed by Paperno et al. (1997), uncoupling 
between otolith and somatic growth rates tends to oc- 
cur under extreme starvation conditions. 
Conclusions 
Our results indicate the entire Punta Banda Estuary 
serves as juvenile habitat for California halibut. This 
suggests that in arid or seasonally regions in which 
estuaries lack in strong environmental gradients, par- 
ticularly in salinity, entire systems may provide suit- 
able habitat for juvenile California halibut. Fodrie and 
Levin (2008) found evidence to suggest that juvenile 
abundance is an adequate proxy for recruitment to 
adult populations in this species. If so, the innermost 
section of Punta Banda Estuary, in which temperature 
and salinity is highest during most of the year, may con- 
tribute the most to the production of adults. In contrast, 
Fodrie and Herzka (2008) used otolith microchemistry 
to evaluate the nursery contribution of juveniles from 
different sections of Punta Banda Estuary to subadult 
production in the adjacent coastline, and found that 
the central and outer sections produced the majority 
of recruits. Considering that juveniles from the inner 
estuary must migrate through the central and outer 
sections of the estuary to emigrate from the system, it 
is possible that Fodrie and Herzka’s (2008) estimates 
of subadult production are biased. If the abundance 
of juveniles is indeed a good proxy for production of 
adults, then the inner section of Punta Banda Estu- 
ary is probably the most important area in terms of 
juvenile California halibut habitat. Put together, these 
studies highlight the need for assessing juvenile habi- 
tat utilization and production on various spatial and 
temporal scales. 
Acknowledgments 
The authors wish to B. Baron, J. P. Lazo and O. Sosa 
for their support and constructive feedback during the 
course of the study, as well as F. Valenzuela, A. Castillo, 
V. Francisco, N. Olivares, J. Sandoval, J. Mariscal, C. 
Rodriguez, and the Department of Research Vessels at 
CICESE for help in the field and laboratory. This proj- 
ect was funded through Basic Research Grant Number 
No. 39571 awarded to S. Z. Herzka by Mexico’s Consejo 
Nacional de Ciencia y Tecnologfa (CONACyT) and by a 
CONACyT Graduate Student Fellowship to F. Lopez- 
Rasgado. 
