343 
Abstract — We evaluated habitat 
quality for juvenile California halibut 
(. Paralichthys californicus) in a Pacific 
Coast estuary lacking in strong salin- 
ity gradients by examining density, 
recent otolith growth rates, and gut 
fullness levels of wild-caught and 
caged juveniles for one year. Juve- 
niles <200 mm standard length were 
caught consistently in the inner, cen- 
tral, and outer sections of the estuary. 
The density of juveniles was two times 
higher in the inner estuary during 
most of the year, consistent with 
active habitat selection by part of the 
population. A generalized linear model 
indicated temperature, sampling time, 
and the interaction between salinity 
and temperature were significantly 
related to density. However, the model 
explained only 21% of the variance. 
Gut fullness levels of wild-caught 
juveniles were highest during the 
summer, but recent otolith growth 
rates were not related to temperature. 
The proportion of individuals feeding 
successfully indicated that seasonal 
differences in food availability are 
more important than spatial varia- 
tion in prey abundance in driving 
feeding success. Feeding success of 
caged fishes was limited, precluding 
the use of growth rates as indicators 
of local habitat quality. However, mar- 
ginal increment widths were reliable 
indicators of somatic growth at low 
growth rates over two-week periods. 
The relatively high growth rates 
and abundance of small wild-caught 
juveniles found throughout the estu- 
ary indicates that the entire estuary 
system has the potential for serving 
as nursery habitat. 
Manuscript submitted 9 July 2008. 
Manuscript accepted 20 April 2009. 
Fish. Bull. 107:343-358 (2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the Nacional 
Marine Fisheries Service, NOAA. 
Assessment of habitat quality for juvenile 
California halibut ( Paralichthys californicus ) 
in a seasonally arid estuary 
Francisco Javier Lopez-Rasgado 
Sharon Z. Herzka (contact author) 
E-mail address for contact author: sherzka@cicese.mx 
Department of Biological Oceanography 
Center for Scientific Research and Higher Education of Ensenada (CICESE) 
Km. 107 Carretera Tijuana-Ensenada 
Ensenada, Baia California, Mexico 
US Mailing address: 
PO Box 434844 
San Diego, California 92143 
California halibut (Paralichthys cali- 
fornicus) is a species of commercial 
and recreational importance that is 
found in coastal waters from Wash- 
ington, U.S.A., to Baja California 
Sur, Mexico (Sweatnam et al., 2007). 
Spawning occurs along coastal areas 
and planktonic larvae inhabit the 
continental shelf for about a month 
before settling in shallow protected 
areas along the coast or in the outer 
reaches of protected embayments 
(Allen and Herbinson, 1990; Moser 
and Watson, 1990). Juveniles make 
facultative use of protected embay- 
ments such as coastal lagoons, bays, 
and estuaries (Horn and Allen, 1985; 
Allen, 1988; Kramer, 1990; Fodrie and 
Mendoza, 2006). Recent studies indi- 
cate that both protected embayments 
and coastal habitats contribute to the 
production of adults, but that juve- 
nile densities are substantially higher 
within embayments (Forrester and 
Swearer 2002; Fodrie and Mendoza, 
2006; Fodrie and Levin, 2008). How- 
ever, there are no studies where juve- 
nile habitat quality has been assessed 
for California halibut on the intra- 
embayment level. 
Juvenile flatfish occupying specific 
habitats or areas within embayments 
may exhibit considerable variability 
in abundance, growth, and mortal- 
ity rates (Allen and Baltz, 1997; Gil- 
liers et al., 2006). In addition, spe- 
cific regions within embayments may 
contribute disproportionaly to the 
production of recruits to the adult 
population (Beck et al., 2001). Sogard 
(1992) reasoned that if rapid growth 
during the juvenile stage offers an 
advantage in terms of increased sur- 
vival, and if growth rates vary as a 
function of habitat quality, individu- 
als will select habitats that offer the 
maximum growth potential, although 
biological interactions such as pre- 
dation can influence habitat choice. 
Within this context, high-quality 
nursery habitats within embayments 
are those in which growth and sur- 
vival rates are higher than the cor- 
responding rates in coastal habitats 
(Gilliers et al., 2006). 
In estuarine systems strongly influ- 
enced by freshwater inflow (“classical” 
estuaries), salinity exhibits strong 
spatial gradients from the mouth to 
the head of the estuary. Gradients 
in salinity have been related to the 
distribution of some species of flatfish 
(e.g., Allen and Baltz, 1997; Able et 
al., 2005). In contrast, estuaries in 
seasonally arid regions, such as the 
Pacific coast of Baja California and 
southern California, tend to receive 
freshwater inflow only during the 
rainy winter season or summer mon- 
soon. These “Mediterranean-type” es- 
tuary systems are increasingly hyper- 
saline with increasing distance from 
the river mouth during a large part of 
the year, and in the inner reaches of 
the estuaries the water exhibits high 
residence times, which influence nu- 
