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Fishery Bulletin 107(3) 
more abundant in unvegetated habitats. Eelgrass is not 
found in the outer and inner sections of Punta Banda 
Estuary and only sparse eelgrass beds are found in the 
central section. We placed cages solely in unvegetated 
areas because eelgrass is not the preferred habitat of 
juvenile halibut. Cages were constructed with a PVC 
frame (1 m widexl m long x 0.5 m high) wrapped in 
Vexar® low-density polyethylene netting of 0.5 x 0.5- 
cm mesh. Cages were closed on the bottom to prevent 
escapement. Similar designs have been used in other 
studies seeking to evaluate the growth of juvenile flatfish 
(Kicklighter, 1990; Sogard, 1992). Caging experiments 
began and ended during spring tides, allowing us access 
to subtidal habitat during lower low water. The day 
before starting each caging experiment, four cages were 
placed within a few meters of each other in the outer, 
central, and inner sections of the estuary (Fig. 1). Each 
cage was anchored by rebar fastened to the corners with 
cable ties. Temperature was measured continuously at 
each caging location by using thermographs placed in 
the vicinity of each caging location (HOBO Water Tem- 
perature Data Loggers model 856097, Onset Computer 
Corporation, Pocasset, MA). These thermographs were 
programmed to record every 30 minutes. 
To supply the cages, individuals within the target 
size range (50-160 mm SL) were placed in ice chests 
filled with aerated seawater immediately after trawling. 
Seawater was exchanged frequently and mortality was 
minimal. Cages were seeded with juveniles caught in 
the same section of the estuary to avoid subjecting them 
to substantial changes in the environmental conditions 
to which they had been exposed. 
The target number of fish to be placed within each 
cage was six. Other flatfish studies have used similar 
fish densities (Kicklighter, 1990). The number of fish 
introduced into each cage was held constant throughout 
the caging experiments. If we did not catch enough fish 
of the targeted size range in a given section of the estu- 
ary, fewer cages were seeded rather than altering fish 
density (Table 1). To evaluate somatic growth during 
the course of the experiment, each juvenile was marked 
by clipping the dorsal or anal fins, or both. Juveniles 
were then injected intramuscularly with tetracycline 
(0.05 mg/kg) to create an otolith mark indicative of the 
beginning of the caging period. To determine the cor- 
rect dose for each individual, wet weights were estimat- 
ed from SL measurements by using a relationship pre- 
viously obtained for juveniles captured in Punta Banda 
Estuary (wet weight (g) = 8.77-0.36SL + 0.0045SL 2 , 
r 2 = 0.99). 
We were concerned about cage loss. Hence, half the 
cages were retrieved after 14 days during lower low 
tide in - 2 cages per section of the estuary) and the re- 
mainder were recovered after 28 days. Otolith growth 
rates were thus measured after a 14- or 28-day caging 
period. Following retrieval from the cages, juveniles 
were identified by their pattern of fin clippings, SL was 
measured, and the number of survivors was recorded. 
Fish were placed on ice in the field and frozen in the 
laboratory for subsequent analysis of otolith growth 
rates and gut fullness levels. Otoliths were removed and 
prepared as described above. It was more difficult to 
visualize daily growth increments in caged individuals 
that in those from natural populations (see also Fodrie 
and Herzka, 2008). Hence, we measured the width of 
the otolith anterior margin from the tetracycline mark 
to the edge. Tetracycline marks were viewed under 400 x 
magnification under ultraviolet light with a FlashUV2 
flashlight (375 nm). Otolith growth rate was expressed 
as pm/day. Individual somatic growth rates of caged 
fishes were calculated as instantaneous growth coef- 
ficients (G, 1/d) with the folowing equation: 
G = ( ln( SL t ) - ln( SL 0 ))/ At , 
where SL t = standard lengths (mm) measured at the 
beginning of a caging period; 
SL 0 = standard lengths (mm) measured at end 
of a caging period; 
4t = number of days fish remained within 
cages. 
We used correlation analysis to examine the relationship 
between otolith and somatic growth rates (G) of caged 
juveniles retrieved after 14 days. 
Gut fullness levels 
Our main objectives were to evaluate whether food avail- 
ability was related to seasonal patterns in recent growth 
rates and to compare the amount of food ingested by 
wild-caught and caged California halibut. We assessed 
the gut fullness level of all juveniles captured in the 
field (n = 456) and those retrieved from cages (n= 214). 
The complete digestive tract (esophagus, stomach, and 
intestine) was dissected whole and preserved in 80% 
ethanol. An index was developed to classify fish by 
their relative gut fullness: 1) empty; 2) 1-25% full; 3) 
26-50% full; 4) 51-75% full; and 5) 76-100% full. Gut 
fullness assessment was performed by a single person 
to maintain consistency. The frequency of occurrence 
of different gut fullness levels for each section of the 
estuary and sampling period was calculated as a per- 
centage of the total caged or wild-caught fish processed 
for a given date. 
Results 
Density and environmental variables 
Mean density of juveniles <200 mm SL ranged from 0.36 
±0.36 to 9.68 ±2.71 fish/1000 m 2 (overall mean=3.31 
±1.07 fish/1000 m 2 , Fig. 2A). It was roughly two times 
higher (—10 fish/1000 m 2 ) in the innermost section 
of the estuary than in the central and outer sections 
( — 4— 5 fish/1000 m 2 ) during the winter and spring. 
Although during summer densities were lower than 
during winter and spring, they were still twice as high 
in the inner estuary than in the central and outer sec- 
