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Fishery Bulletin 107(3) 
behavior typically exhibit by flatfish in response to pre- 
dation pressure or as part of their ambush feeding be- 
havior (Haaker, 1975; Allen, 1990; Amezcua and Nash, 
2001). We did not evaluate sediment grain size during 
our study. However, Ortiz et al., (2003) reported that 
in Punta Banda Estuary sediment grain size ranges 
from fine sand (0.19-0.93 mm) near the mouth of the 
to coarse silt (0.03 mm) near the head. We found that 
density was generally highest in the innermost reaches 
of the estuary, where sediments are finest. Hence, the 
higher abundance of juveniles in the inner estuary may 
be at least partially related to the characteristics of the 
substrate. 
There is consistent evidence to suggest that the peak 
in estuarine immigration occurs primarily during win- 
ter and spring (Allen, 1988; Kramer, 1990; Hammann 
and Ramirez-Gonzalez, 1990; Valle et al., 1999), al- 
though settlement can also take place during the sum- 
mer months (Allen et al., 1990). Based on analysis of 
the long-term larval surveys preformed as part of the 
California Cooperative Oceanic Fisheries Investiga- 
tions Program (CalCOFI), Moser and Watson (1990) 
reported that off the coast of northern Baja California 
and in southern California, the peak in larval abun- 
dance occurs between February and April, with a sec- 
ondary peak during summer. We observed the highest 
abundance of recent recruits (40-50 mm SL) during 
winter and spring. There was secondary peak of small 
juveniles during the summer, which could reflect either 
estuarine recruitment (the recent ingress of juveniles 
into the system) or growth of previous recruits that 
entered the estuary at a very small size. 
The marked decrease in the density of juveniles >150 
mm SL that we observed during the summer is strongly 
suggestive of estuarine emigration. Although size-selec- 
tive mortality of larger juveniles (Sogard, 1997) could 
also lead to a decrease in density, the decrease occurred 
primarily in the inner and central estuary and was ac- 
companied by an increase the in abundance of larger 
juveniles in the outer section, which is consistent with 
movement toward the mouth of the estuary. Given that 
estuarine emigration coincided with the onset of higher 
temperatures within Punta Banda Estuary, tempera- 
ture gradients may provide the cue for emigration. 
Lastly, late juveniles >200 mm SL and adults were 
captured throughout Punta Banda Estuary, albeit in 
low numbers. Spawning only occurs in coastal areas 
(Haaker, 1975). The presence of late juveniles and 
adults within the estuary suggests that these systems 
may serve as feeding grounds for larger halibut, despite 
their predominantly coastal habits (Haaker, 1975; Al- 
len, 1990). 
Otolith growth rates of 
natural populations and gut fullness 
The daily otolith growth rates of the fastest (Octo- 
ber 2004; 7.32 pm/d) and slowest (September 2005; 
4.54 pm/d) growing juveniles 50-160 mm SL varied 
approximately two-fold during the study. These values 
are within the range of daily otolith growth rates 
reported for juvenile fishes (Sogard and Able, 2002; 
Gilliers et al., 2006). Recent otolith growth rates varied 
significantly as a function of time and section of the 
estuary, although juveniles grew throughout the year. 
This indicates spatial and temporal variability in the 
quality of juvenile habitat within the estuary (Sogard, 
1992; Phelan et al., 2000; Necaise et al., 2005). Tem- 
perature, food availability and quality, size and preda- 
tion pressure are considered the most important factors 
influencing growth in juvenile flatfish (Gibson, 1994). 
We did not find a relationship between the average 
temperatures and recent otolith growth, although other 
studies on California halibut indicate that an increase 
in temperature from 20° to 23°C leads to higher somatic 
growth rates in the absence of food limitation (Haaker, 
1975; Gadomski and Caddell, 1991). This could indi- 
cate that temperature does not substantially influence 
otolith growth rates (Campana and Jones, 1992). How- 
ever, Kicklighter (1990) reported a significant linear 
relationship (r=0.69, P<0.001) between temperature 
and otolith growth rates in caged juvenile California 
halibut held at a single site. We found a significant 
negative correlation between somatic growth rates and 
temperature in our caged fish, although the growth 
rates were very low. Hence, although there is evidence 
to suggest temperature does influence otolith growth 
in juvenile California halibut, for wild-caught juve- 
niles, other physical or biological factors play a more 
important role. 
California halibut are primarily diurnal, visual feed- 
ers (Haaker, 1975). During our study, 40-85% of indi- 
viduals exhibited some degree of feeding (gut fullness 
levels >0%). Likewise, Plummer et al. (1983) found that 
46% of juveniles and young adults (124-176 mm SL) 
captured in coastal waters using an otter trawl exhib- 
ited empty stomachs. Wertz and Domier (1997) reported 
that 69% of fish 156-1055 mm TL had empty stomachs. 
