Parnel et al.: Effects of oceanic conditions on ichthyoplankton communities in the Columbia River plume 
167 
nately a spring-summer (May-July) 
group dominated by northern anchovy, 
sanddab, and blacksmelt (Fig. 4). 
Among the larvae, Pacific sandlance 
( Ammodytes hexapterus), rex sole, and 
curlfin sole ( Pleuronichthys decurrens) 
were tightly clustered, as were northern 
anchovy and thornyheads ( Sebastolo - 
bus spp.) (Fig. 5). The remaining larger 
clusters consisted of mainly flatfishes 
and Pacific tomcod. Sampling clusters 
were less defined for larval fish than 
for eggs (Fig. 5). Cluster A consisted of 
samples collected from multiple years 
and months, and most were collected 
before the spring transition. No spe- 
cies dominated these collections. In 
contrast, Cluster B was dominated by 
Pacific tomcod and Dover sole (Micros- 
tomus pacificus). Cluster C occurred 
entirely during May and June and was 
distinguished by the high abundance of 
northern anchovy (Fig. 5). 
There were very limited differences 
in the biological or physical oceano- 
graphic conditions between the two 
sampling stations. Only salinity was 
significantly different between the two 
stations U-test, P<0.05). Temperature, 
chlorophyll a, zooplankton densities, 
and densities of the five most abun- 
dant ichthyoplankton species were not 
significantly different between stations. 
However, there were significant annual 
differences in temperatures (ANOVA, 
P<0.05), but not salinities or chloro- 
phyll a at these stations during the 
study period (Table 3). There were also 
large annual differences in the date 
of the spring transition (Table 3). The 
BVSTEP analysis revealed that tem- 
perature explained most of the inter- 
annual variation in the ichthyoplank- 
ton community (Spearman p=0.345), 
(p ranges from -1 to 1, where values 
farthest from zero indicated a stron- 
ger correlation) followed by salinity 
(p = 0.194) and Columbia River flow 
(p=0.145). Chlorophyll a and overall 
ichthyoplankton densities did not pro- 
vide any explanatory power and did not 
relate to variations in ichthyoplankton 
species composition. 
The egg and larval fish data showed 
very few differences when these data 
were grouped and compared by year, 
season, and station. MRPP analysis 
revealed few significant differences be- 
tween groups (Table 4). The taxonomic 
composition of the dominant egg or 
Eggs 
Information remaining (%) 
25 50 75 
1 h 
100 
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7-18-04 
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5-19-00 
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EI El 
6-3-03 
m 
7-11-00 
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BBH 
5-21-03 
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5-19-04 
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5-8-01 
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IB 
6-14-03 
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□□□□□□ 
6-27-02 
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□□□□□□ 
5-30-04 
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5-4-03 
mm 
7-17-03 
9IBB 
6-24-04 
■ ■■■ 
Figure 4 
Two-way cluster analysis of egg densities by sampling date. The taxa 
clusters are oriented vertically at the top of the figure and sampling 
date clusters are oriented horizontally at the left side of the figure. The 
dashed lines delineate sampling dates that contained similar assemblages 
of eggs. The color of the boxes denotes relative abundance of each taxon 
during each sampling period as shown in the matrix coding legend. The 
taxa names are abbreviated as: Cith. spp. ( Cithariclithys spp.), E. mord. 
( Engraulis mordax ), Bathyl (Bathylagidae), Pleuron. ( Pleuronectidae ), 
G. zach. (Glyptocephalus zachirus), L. exil. (Lyopsetta exilis), M. pad. 
(Microstomus pacificus), P. vetu. ( Paroplirys vetulus), Seb. spp. ( Sebas - 
tolobus spp.), P. decu. (Pleuronichthys decurrens), P. rnela. (Psetticthys 
melanostictus), and T. symm. (Tracliurus symmetricus). “Information 
remaining” is a scaled measure of the amount of information that is left 
after stations are grouped. 
