Donohoe: Age, growth, distribution, and food habits of Atractoscion nobilis 
71 1 
turn was also sampled with a 1 m x 6 m beach seine. 
Three hauls were made in each block over a mea- 
sured distance of 15-50 m with the width of the seine 
fixed at 4 m. In addition, three tows were made each 
month in blocks 2-5 of the 2-4 m stratum in Mission 
Bay with the 1.6-m beam trawl (Fig. 1). The mesh 
size of all three nets was 3 mm. All hauls were made 
during the day. Monthly sampling in Agua Hedionda 
Lagoon was not initiated until March 1987. 
Tow distance, water temperature, and the pres- 
ence and type of drift macrophytes in the net were 
recorded at the end of every tow. Beginning in April 
1988, the weight of drift macrophytes in each tow 
was also recorded at the four coastal sites sampled 
by SDSU biologists. White seabass were either fro- 
zen or preserved in 80% ethanol and later measured 
to 0.1 mm standard length (SL) in the laboratory. 
Lengths of alcohol-preserved fish were adjusted by 
3.6% to compensate for shrinkage. Average shrink- 
age was estimated by measuring a subsample of 
white seabass before and several months after pres- 
ervation in ethanol. Sagittae and stomach contents 
were removed and stored in 80% ethanol. Fish were 
then dried at 60°C for two days and weighed. 
White seabass were also obtained opportunistically 
(i.e. sporadically) from the coastal habitat with a 7.6-m 
headrope otter trawl and a 15.2-m beach seine (6-mm 
mesh). These fish were used only in the food habits 
and growth portions of this study. 
Distribution and abundance 
Abundance was calculated as the number of fish 
caught divided by the product of tow distance (from 
odometers) and net width. Mean abundance of fish 
along the coast was calculated for each site by depth 
stratum (n = 4 tows). Monthly differences in abun- 
dance among the three depth strata were compared 
by using the Kruskal-Wallis test, with a=3 depths, 
and n = 4 (1987) or n = 8 (1988) sites (Sokal and Rohlf, 
1981). Monthly mean abundance in bays was calcu- 
lated for each bay by block and depth stratum. Block 
means were averaged to produce a mean for each 
bay and the two bays were averaged to yield a grand 
mean for each depth stratum. Because estimates of 
monthly mean abundance did not differ among the 
two gear types (paired £-test; mean difference=0.50 
fish/ha, £=0.27, df=8, P=0.79), trawl and seine 
samples within the 0-1 m depth stratum were pooled 
to produce an improved estimate of abundance. 
The relation between abundance of white seabass 
and drift macrophytes was estimated by testing for 
a correlation between abundance of white seabass 
and drift macrophytes in each tow and for a correla- 
tion between mean abundances at each site (n= 4 
tows). Abundance of macrophytes (g/m 2 ) was log- 
transformed prior to analysis. Biomass of macro- 
phytes was recorded only from April to October 1988 
at the four secondary sites along the coast that were 
sampled by SDSU biologists. 
Food habits 
The stomach contents of 142 white seabass collected 
in bays and along the coast with all gear types were 
examined. For each fish, prey items were identified, 
counted, sorted into one of ten major prey categories, 
dried at 60°C for 1-2 d, and weighed to either 1 pg (for 
samples <25 mg) or to 0.1 mg (for samples >25 mg). 
White seabass were grouped into six length classes: 6- 
10, 10-18, 18-25, 25-35, 35-55, and 55-150 mm SL. 
Class intervals were chosen so that each interval con- 
tained similar numbers of fish. Mean prey weight and 
frequency of occurrence of each prey category were cal- 
culated for the six length classes. Six individuals with 
empty stomachs were excluded from calculations of fre- 
quency of occurrence and mean weight of prey. 
Age and growth 
The ageing method was validated by using labora- 
tory-reared fish of known age. Eggs obtained from 
captive broodstock were placed in 7-m 3 flow-through 
tanks and reared at 17-20°C on a diet of marine ro- 
tifers, brine shrimp, euphausids, and chopped mack- 
erel. White seabass were sacrificed at irregular in- 
tervals between 13 and 76 d after hatching and stored 
in 80% ethanol. Sagittae were mounted in Eukitt 
mounting media and ground in the sagittal plane 
with 15-pm grit sandpaper and polished with 0.3-pm 
grit lapping film. Increments were counted on the 
right sagitta from the central primordium to the mid- 
ventral margin. Each sagitta was read in one ses- 
sion by one observer, with neither age nor length of 
the fish known to the reader. The rate of increment 
deposition and age at first increment formation were 
estimated by linear regression. 
A subsample of 50 wild larval and juvenile white 
seabass was aged with the technique described above. 
Individuals were selected at random from several 
length classes to represent equally the size range of 
fish collected. The subsample included fish caught 
in bays, on the coast, and in both years. Growth rates 
were estimated by fitting a Gompertz function (L t = 
L o e Gl1 ~ e4,) ) j- 0 length-at-age and weight-at-age data. 
The ages of the remaining individuals were estimated 
from the resulting age-length relation. The date each 
fish was spawned was calculated by subtracting the 
age of the fish and an additional two days (incuba- 
tion time at ~16°C; Orhun, 1989) from date of cap- 
