32 
Fishery Bulletin 95(1), 1997 
tively, and between 49% and 91% by weight of the 
diet of spring chinook salmon. 
Larval crab (anomuran and brachyuran) prey were 
a moderately important component of the diet of the 
two smallest length classes of fall chinook salmon 
(<80 mm FL and 81-100 mm FL) and of the two larg- 
est length classes of spring chinook salmon ( 121-141 
mm FL and >141 mm FL), representing 7% and 2%, 
and 2% and 3% of total food by weight, respectively 
(Table 2). However, crab larvae of various taxa and 
at different developmental stages were consumed by 
chinook salmon of different stock and length groups. 
The smallest fall chinook salmon (<80 mm FL) fed 
mainly on porcellanid, pinnotherid, callianassid, and 
unidentified brachyuran zoea rather than on 
megalopae (95% zoea and 5% megalopae by weight), 
whereas larger fall chinook salmon (81-100 mm FL) 
fed more on megalopae than on zoea (69% vs. 31% 
by weight), and the large spring chinook salmon 
(>121 mm FL) fed exclusively on megalopae, mainly 
large Cancer magister (72%), Cancer oregonensis 
(19%), and Cancer sp. (4%). 
Gammarid amphipods were also a fairly important 
component of the diet of the small fall chinook 
salmon, representing 4% and 5% by weight for fish 
<80 mm FL and 81-100 mm FL, respectively, but 
were a less important component of the diets of the 
largest fall chinook salmon (>101 mm FL) and spring 
chinook salmon (Table 2). 
Dietary overlap, based on the 14 major prey cat- 
egories was low (<0.55) between the smallest fall 
chinook salmon (<80 mm FL) and all other length 
categories of fall and spring chinook salmon (Table 
3) . This reflects the reduced relative importance of 
fish and the greater relative importance of insects 
and crab larvae in the diet of the smallest fall chinook 
salmon than in the diet of larger fish (Table 2). Exclud- 
ing the smallest fall chinook salmon, diet overlap was 
high for eight of ten comparisons among length groups 
of fall and spring chinook salmon (Table 3). 
Dietary overlap, in respect to the lowest identified 
taxa (86 categories) was also low between fall chinook 
salmon <80 mm FL and all other groups. Overlap 
among the other groups was generally higher than 
that with the small fall chinook salmon but was >0.60 
for only four of the ten comparisons. 
Diets by location 
Dramatic differences in the diets of fall and spring 
chinook salmon were associated with where the fishes 
were caught in the bay. For both salmon groups, fish 
were a much more important component of the diet 
at lower-bay stations 1-3 than at mid-bay stations 
4-5 (Table 4). Conversely, barnacle molts and algae 
made up a much larger fraction of stomach contents 
at mid-bay stations than at lower-bay stations (Table 
4) . Dietary overlap based on the 14 major food cat- 
egories was high between fall and spring chinook 
salmon caught in the same areas of the bay but was 
low for all comparisons of salmon caught in the two 
different areas of the bay (Table 5). Dietary overlap 
based on the 86 lower taxonomic categories was also 
highest for fall and spring chinook salmon caught in 
the same area of the bay, but only for fish caught in 
the lower bay was the overlap value >0.60 (Table 5). 
Table 3 
Dietary overlap of different length groups of fall and spring chinook salmon. Overlap values based on 14 major food categories are 
in normal type and those based on 86 lower taxonomic categories are in italics. High overlap values (>0.60) are in bold type. 
Fall chinook 
salmon FL (mm) 
Spring chinook 
salmon FL (mm) 
81-100 
>101 
101-120 
121-140 
>141 
Fall chinook salmon FL (mm) <80 
0.55 
0.25 
0.48 
0.44 
0.27 
0.36 
0.13 
0.25 
0.21 
0.07 
81-100 
— 
0.68 
0.70 
0.79 
0.70 
0.56 
0.57 
0.67 
0.46 
>101 
— 
— 
0.55 
0.74 
0.94 
0.35 
0.63 
0.72 
Spring chinook salmon FL (mm) 101-120 



0.80 
0.56 
0.63 
0.32 
121-140 
— 
— 
— 
— 
0.74 
0.59 
