Fisher and Pearcy: Dietary overlap of juvenile fall- and spring-run Oncorhynchus tshawytscha 
31 
Table 1 
Percentage by weight and frequency of occurence (in parentheses) of fourteen major food categories in stomachs of juvenile fall- 
run and spring-run chinook salmon caught in 1987 in Coos Bay. Numbers in brackets are sample sizes. 
Fall chinook salmon Spring chinook salmon 
Food category [116] [65] 
Cirripedia molts 
5 
(47) 
12 
(51) 
Isopods 
<1 
(9) 
<1 
(11) 
Caprellid amphipods 
1 
(14) 
<1 
(11) 
Gammarid amphipods 
4 
(41) 
1 
(43) 
Brachyuran, anomuran larvae 
2 
(27) 
2 
(35) 
Other decapod larvae 
<1 
(8) 
<1 
(2) 
Crustacean fragments 
5 
(20) 
1 
(25) 
Araneae 
<1 
(14) 
<1 
(5) 
Insects 
8 
(80) 
1 
(60) 
Other arthropods 
<1 
(6) 
<1 
(2) 
Molluscs 
<1 
(4) 
<1 
(12) 
Teleosts 
64 
(40) 
65 
(37) 
Algae, plants 
7 
(46) 
16 
(68) 
Other material 
4 
(43) 
2 
(55) 
Table 2 
Percentage by weight and frequency of occurence (in parentheses) of fourteen major food categories in stomachs of different size 
groups of fall and spring chinook salmon caught in 1987 in Coos Bay. Numbers in brackets are sample sizes. 
Food category 
Fall chinook salmon FL (mm) 
Spring chinook salmon FL (mm) 
<80 
[32] 
81-100 
[73] 
>101 
[11] 
101-120 
[39] 
121-140 
[19] 
>141 
[7] 
Cirripedia molts 
9(63) 
5 (45) 
3(18) 
22 (62) 
9 (42) 
<1 (14) 
Isopods 
<1 (9) 
<1 (10) 
0 
<1 (10) 
<1 (16) 
0 
Caprellid amphipods 
1 (9) 
1 (18) 
0 
<1 (8) 
<1 (16) 
<1 (14) 
Gammarid amphipods 
4 (44) 
5 (42) 
<1 (18) 
1 (51) 
1 (37) 
<1 (14) 
Brachyuran, anomuran larvae 
7 (25) 
2 (32) 
0 
1 (28) 
2 (42) 
3 (57) 
Other decapod larvae 
<1 (13) 
<1 (7) 
0 
0 
<1 (5) 
0 
Crustacean fragments 
11 (22) 
6 (22) 
0 
2 (23) 
1 (32) 
<1 (14) 
Araneae 
<1 (13) 
<1 (16) 
0 
<1 (5) 
<1 (5) 
0 
Insects 
26 (94) 
7 (81) 
1 (36) 
1 (69) 
<1 (63) 
0 
Other arthropods 
<1 (13) 
<1 (4) 
0 
0 
<1 (5) 
0 
Molluscs 
1 (6) 
<1 (4) 
0 
<1 (5) 
<1 (26) 
<1 (14) 
Teleosts 
18 (9) 
62 (45) 
94(91) 
49 (31) 
68 (32) 
91 (86) 
Algae, plants 
12(56) 
7 (42) 
2(36) 
20 (72) 
18 (63) 
4(57) 
Other material 
11 (59) 
4 (38) 
<1 (27) 
4 (59) 
<1 (42) 
2(71) 
smallest fall chinook salmon ( <80 mm FL) than in 
the diets of the other length groups of both fall and 
spring chinook salmon. Insect prey made up 26% of 
food by weight in stomachs of the smallest fall 
chinook salmon (Table 2). The insect fraction of the 
diet dropped to 7% and 1% for larger fall chinook 
salmon 81-100 mm FL and >101 mm FL, respec- 
tively, and was <1% for all length groups of spring 
chinook salmon. Fish made up only 18% by weight 
of the diet of fall chinook salmon <80 mm FL, but 
62% and 94% by weight of the diet of fall chinook 
salmon 81-100 mm FL and >101 mm FL, respec- 
