Landingham et a I.: Feeding habits of juvenile Pacific salmon 
289 
16-95% of the actual number of stomachs 
analyzed (Fig. 2). The highest cumulative 
numbers of prey taxa in - 25 and 26, respec- 
tively) were observed after we had ran- 
domly subsampled 86 coho and 396 pink 
salmon stomachs (Fig. 3). Virtually all 
chinook salmon analyzed (39) were needed 
to reach the 14 cumulative prey taxa ob- 
served. The curves of cumulative number 
of taxa for pink and chum salmon were 
more similar than for any other pair of 
species (Fig. 3). 
Pink salmon The prey of juvenile pink 
salmon (85-222 mm FL; x =142 mm; 
SD=22.9) encompassed 26 taxa and sev- 
eral life-history stages. Hyperiid amphi- 
pods, especially the genus Themisto, had 
the highest total IRI (Fig. 4) and highest 
FO and mean abundance over all periods 
and habitats (Table 3). Juvenile fish had 
the second-highest IRI and the greatest 
biomass — 76% of pooled weight of stom- 
ach contents. In 1984, the IRI for fish prey 
did not rank first, but it was more than 
twice the 1983 value; fish prey ranked 
higher in Alaska than in British Colum- 
bia. Tunicates, primarily the larvacean 
Oikopleura dioica, were the third most 
important prey in pooled samples. 
Chum salmon The prey spectrum for ju- 
venile chum salmon (80-276 mm FL; 
x=151 mm; SB=28.4) included 22 taxo- 
nomic groups and several life-history 
stages. Juvenile fish, tunicates (salps and 
the larvacean O. dioica ), and hyperiid 
amphipods ( Themisto spp.) had the high- 
est IRI’s overall (Fig. 5). 
Sockeye salmon The prey spectrum for 
juvenile sockeye salmon (91-202 mm FL; 
v = 1 5 1 mm; SD=18.9) encompassed 18 
taxonomic groups and several life-history 
stages. Fish prey had the highest IRI 
(40.3%) and the greatest average weight 
(87.2%) pooled over all habitats and peri- 
ods (Table 3; Fig. 6), although no fish were 
sampled from outer-coast inlets (Table 1). 
Fish prey were more important in 1984 
than in 1983, especially in the outside 
waters of southeastern Alaska in July 1984 
and inside inlets and outside waters (>37 
km) in August 1984 (Fig. 6). Hyperiid am- 
phipods ( Themisto spp.) were the second 
Table 2 
Prey from juvenile salmon stomachs as index of relative importance 
(IRI). IRI = (N + W)FO, where N= numerical percentage, W = weight 
percentage, and FO - frequency of occurrence percentage. Numbers in 
parentheses are totals of taxonomic groups for which more than one 
taxon is listed. 
IRI (%) 
Prey 
Pink 
Chum 
Sockeye 
Coho 
Chinook 
Polychaeta 
Unidentified 
<0.01 
<0.01 
<0.01 
<0.01 
Mollusca 
(0.90) 
(0.16) 
(0.17) 
(0.02) 
(— ) 
Gastropoda 
Limacina helicina 
0.82 
0.16 
0.15 
0.02 
Bivalvia 
Unidentified 
<0.01 
<0.01 
Cephalopoda 
Unidentified 
0.08 
<0.01 
0.02 
<0.01 
0.18 
Copepoda 
(3.71) 
(2.93) 
(4.15) 
(0.02) 
(<0.01 ) 
Neocalanus 
cristatus 
<0.01 
Epilabidocera 
longipedata 
<0.01 
<0.01 
Unidentified 
3.70 
2.93 
4.14 
0.02 
<0.01 
Cumacea 
Unidentified 
<0.01 
<0.01 
Amphipoda 
Hyperiidea 
(39.61) 
(28.03) 
(36.48) 
(6.84) 
(0.10) 
Hyperia sp. 
0.01 
0.01 
0.01 
0.02 
0.01 
Themisto spp. 
38.75 
27.44 
36.11 
6.73 
0.08 
Primno macropa 
0.83 
0.58 
0.36 
0.09 
0.01 
Vibilia sp. 
0.02 
<0.01 
0.01 
<0.01 
— 
Euphausiacea 
(5.95) 
(6.18) 
(12.62) 
(3.88) 
(18.34) 
Euphausia paeifica 
<0.01 
— 
— 
<0.01 
— 
Thysanoessa spinifera <0.01 
0.01 
— 
0.01 
0.08 
Unidentified 
5.94 
6.17 
12.62 
3.86 
18.26 
Decapoda 
Unidentified 
4.67 
3.16 
3.64 
25.26 
4.81 
Insecta 
Unidentified 
0.01 
<0.01 
<0.01 
0.01 
Chaetognatha 
Unidentified 
0.01 
0.01 
<0.01 
<0.01 
Urochordata 
(tunicates) 
(13.56) 
(30.32) 
(2.26) 
(0.03) 
Salpidae 
Unidentified 
<0.01 
0.21 
<0.01 
Larvacea 
Oikopleura dioica 
13.56 
30.11 
2.26 
0.03 
Osteichthyes 
(31.11) 
(29.88) 
(40.27) 
(63.78) 
(76.42) 
Clupea pallasi 
— 
— 
— 
0.01 
0.26 
Osmeridae 
<0.01 
0.02 
— 
<0.01 
0.61 
Myctophidae 
0.02 
0.02 
<0.01 
— 
— 
Theragra 
chalcogramma 
0.01 
Sebastes spp. 
0.04 
— 
0.03 
0.04 
— 
Cottidae 
— 
— 
— 
<0.01 
— 
Stichaeidae 
<0.01 
— 
<0.01 
<0.01 
0.02 
Ammodytes 
hexapterus 
<0.01 
0.03 
0.30 
0.47 
Pleuronectidae 
— 
<0.01 
<0.01 
0.02 
— 
Unidentified 
31.04 
29.80 
40.22 
63.39 
75.06 
