Van Noord et al.; Oceanographic influences on the diet of myctophids in the eastern Pacific Ocean 
281 
Table 3 
Summary of stomach contents (including pieces of plastic) of 3 myctophid species collected in the eastern tropical Pa- 
cific Ocean during 2006. Diet indices include mean percentages by number (MNi), weight {MWi), and percent occurrence 
(0,). Fourteen of the 17 prey groups used in the classification tree analysis are designated with an “X.” Unidentifiable 
and rare individuals (generally contributing <1% MNi to the diet) within the broader taxonomic group are not displayed. 
CART=classification and regression tree analysis. Bold font represents total values for a subclass and order of prey. 
Used (X) 
in CART 
Myctophum 
nitidulum 
Symbolophorus 
reuersus 
Gonichthys 
tenuiculus 
MNi 
MWi 
Oi 
MNi 
MW, 
o, 
MN, 
MW, 
O, 
Copepoda 
42.7 
39.1 
69.6 
32.S 
28.3 
50.3 
18.6 
17.6 
7.3 
Calanoida 
36.4 
37.5 
62.5 
27.1 
23.3 
45.2 
18.6 
17.6 
7.3 
Calanidae 
X 
1.01 
1.44 
10.7 
0.29 
0.15 
1.51 
3.85 
4 
1.22 
Candaciidae — Candacia spp. 
X 
1.47 
1.84 
14.4 
5.53 
5.04 
16.1 
0 
0 
0 
Eucalanidae 
X 
1.79 
2.51 
14.4 
0.12 
0.27 
1 
0 
0 
0 
Euchaetidae 
X 
7.33 
10.2 
32.1 
6.94 
15 
15.1 
3.85 
4 
1.22 
Pontellidae 
X 
0.5 
0.64 
6.69 
0 
0 
0 
3.01 
2.44 
2.44 
Cyclopoida 
6.26 
2.89 
35.5 
5.33 
4.99 
14.1 
0.55 
0 
1.22 
Corycaeidae — Corycaeus spp. 
X 
1.43 
0.56 
12.7 
0.37 
0 
1.51 
0 
0 
0 
Oncaeidae — Onceaea spp. 
X 
4.8 
2.33 
27.4 
4.73 
1.81 
13.6 
0 
0 
0 
Ostracoda 
41.5 
39.1 
45.5 
24.4 
18.1 
26.1 
34.6 
36 
11 
Cypridinidae — Cypridina americana 
X 
41.3 
38.8 
45.1 
24.4 
18.1 
26.1 
34.6 
36 
11 
Euphausiacea 
X 
3.29 
3.42 
13 
29.6 
34.5 
47.2 
19.4 
16.4 
7.32 
Euphausia diomedeae 
0 
0 
2.86 
6.53 
0 
0 
E. mutica 
0.08 
0.67 
4.15 
10.1 
0 
0 
E. tenera 
0.16 
2.01 
2.34 
8.04 
0 
0 
Euphausia spp. 
2.18 
10 
19.6 
7 
19.4 
7.32 
Amphipoda 
8.38 
12.1 
35.8 
7.58 
9.61 
20.1 
27.3 
30 
9.76 
Hyperiidae 
X 
3.86 
5.42 
20.1 
4.6 
5.32 
15.1 
9.34 
11.5 
3.66 
Pronoidae 
X 
1.23 
2.54 
8.36 
0.24 
0.37 
3.02 
4.81 
6 
2.44 
Platyscellidae 
X 
0.32 
1.11 
3.34 
0.3 
1.09 
3.02 
0 
0 
0 
Mollusca 
X 
2.98 
4.35 
14.7 
2.48 
3.59 
8.54 
0 
0 
0 
Atlantidae 
0.12 
0.32 
2.01 
0.39 
0.75 
2.51 
0 
0 
0 
Janthinidae 
1.44 
1.99 
8.01 
1.42 
1.8 
2.51 
0 
0 
0 
Limacinidae — Limacina spp. 
0.4 
0.48 
1 
0 
0 
0 
0 
0 
0 
Cavoliniidae — Diacria schmidti 
0.03 
0.16 
0.67 
0.03 
0.16 
0.5 
0 
0 
0 
Unidentified Mollusk 
0.98 
1.35 
5.69 
0.64 
0.88 
3.02 
0 
0 
0 
Larval fish 
X 
0.12 
0.19 
0.33 
2.09 
3.63 
7.04 
0 
0 
0 
Decapoda 
0.33 
0.47 
3.01 
1.09 
1.86 
3.02 
0 
0 
0 
Fish egg 
0.78 
0.16 
3.34 
0.08 
1.21 
0.5 
0 
0 
0 
Cephalopoda 
0 
0 
0 
0.19 
0.3 
0.5 
0 
0 
0 
Plastic 
2.01 
0 
1.22 
Total stomachs 
299 
199 
82 
titioned the diet composition for 271 myctophids sam- 
pled east of 100°W, on the left side of the tree (node 2), 
from the diet composition of 196 myctophids sampled 
west of 100°W, on the right side of the tree (i.e., ter- 
minal node 3) (Figs. 6 and 7). Ostracod composition 
in the zooplankton was a strong competitor-split vari- 
able, i.e, ostracod composition in the zooplankton pre- 
formed only 2% worse than longitude at this partition 
(node 2). The diet composition of the myctophids east 
of 100°W was variable, and the tree further separated 
169 samples caught in waters of relatively high salin- 
ity, SSS >32.86, east of 100°W (terminal node 4) from 
102 samples caught in waters of relatively low salinity, 
SSS <32.86, east of 100°W and near the Panama Bight 
(terminal node 5 [Figs. 6 and 7]). 
Terminal node 3 All myctophids in the offshore re- 
gion (Fig. 7) consumed large proportions of the os- 
tracod Cypridina americana (mean MAC,: 76.4%) and 
small numbers of several other prey (Fig. 7). The diet 
diversity (0.22) of the myctophids in this region (ter- 
minal node 3) was lowest among all terminal nodes. 
Ostracods were the most numerically abundant and 
the MLD was the deepest at the 13 stations within the 
offshore region. 
Terminal node 4 The 169 myctophids residing in ter- 
minal node 4 consumed large proportions of copepods 
(mean MNf. 66.6%) that were identifiable as euchae- 
tids. These myctophids were captured at 9 stations at 
intermediate distances from the coast, between 100°W 
