Donohoe: Age, growth, distribution, and food habits of Atractoscion nobilis 
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Figure 4 
Monthly mean abundance of white seabass (± 1 SE) in the 4-8 m stra- 
tum along the coast ( 1987 n=A sites; 1988 n=8 sites) and in the 0-1 m 
stratum in the bays <n= 2 bays). Means that are significantly different 
from those in the 9-11 and 12-14 m strata (usually zero — not shown) 
are indicated (Kruskal-Wallis test, ** = P<0.01; *** =P<0.001). 
stratum during these nine months. Be- 
cause most tows in the 4-8 stratum caught 
no white seabass, the variance associated 
with the estimates of abundance within 
the stratum was high. As a result, abun- 
dance in the 4-8 m stratum did not differ 
statistically from that in the 9-11 and 12- 
14 m strata (generally zero) except in June 
1987 and from June to July 1988 (Kruskal- 
Wallis test, P<0.05, n=4 or 8). The tem- 
perature in the 4-8 m stratum during the 
summer ranged from 16 to 20°C, an aver- 
age of 1.2 and 1.8°C warmer than the two 
deeper strata. 
Although the relative abundance of 
settled white seabass was lower in the 
bays than along the coast, the two esti- 
mates could not be compared statistically 
because different nets were used to sample 
the two habitats. In addition, only 10 fish 
were caught in the two bays, making esti- 
mates of abundance sensitive to capture 
of individual fish. Estimates of mean den- 
sity in the 0-1 m stratum in the bays from 
April to August ranged from 0 to 5 per ha 
in 1987 and from 0 to 10 per ha in 1988 
(Fig. 4). The high April 1988 estimate re- 
sulted from a single fish caught in a short 
tow. Mean abundance during these five 
months (total catch total area swept) was 
1.3/ha in 1987 and 3.1/ha in 1988. Monthly 
estimates for bays were about 0.8-12 times 
lower than estimates for the coast during the same 
period. 
Abundance of white seabass within the 4-8 m 
coastal stratum was related to the abundance of drift 
macrophytes. Drift macrophytes were common in the 
4-8 m stratum and were recorded in 188 of 205 tows 
(92%) made during the nine months when white 
seabass were present. Macrophytes were present in 
49 of 52 tows (94%) that caught white seabass. The 
drift material was mainly giant kelp ( Macrocystis 
pyrifera ) and surf grass ( Phyllospadix torreyi ), but 
filamentous red and other brown algae were domi- 
nant at times. In 1988, weight of macrophytes in each 
tow was recorded at the four sites sampled by SDSU 
biologists. At these sites, abundance of white seabass 
in each tow was weakly correlated with the abun- 
dance of drift macrophytes in each tow in the 4-8 m 
coastal stratum (n= 77, r- 0.29, P=0.01, Fig. 5A). Be- 
cause white seabass were not abundant, an average 
of the four tows made at each site was also calcu- 
lated. Mean abundance of white seabass at each site 
(n= 4 tows) and mean abundance of drift macrophytes 
were more strongly correlated (n = 21, r=0.52, 
P=0.015, Fig. 5B). Drift macrophytes were also 
present in the two deeper strata, but only three white 
seabass were caught at those depths. 
Food habits 
Along the coast, white seabass of all length classes 
fed almost exclusively on mysid crustaceans. For each 
length class, mysids composed from 74% to 99% of 
the diet by weight and were found in 78-100% of 
stomachs that contained food (Table 1). These mysids 
were not identified to species but were probably 
Metamysidopsis elongata, the numerically dominant 
mysid in the nearshore coastal habitat (Clutter, 1967; 
Roberts et al., 1982). Larger white seabass ate larger 
mysids, although fish >0.2 g dry weight (~40 mm SL) 
fed on mysids of similar mean weight (Fig. 6). Mysids 
also dominated the diet of the 10 fish caught in the 
bays. 
Prey of secondary importance varied with white 
seabass length class. Larvae (6-10 mm SL) fed on 
copepods, fish of intermediate length ( 10-55 mm SL) 
fed on gammarid amphipods, and larger juveniles 
