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Fishery Bulletin 1 10(4) 
Table 2 
Frequency of occurrence (%) for all fish species caught in open waters of the lower Columbia River estuary by year during our 
study during 2007-10. Life history stages: j=juvenile, a=adult, or subadult, with the “0” and “1” indicating subyearling and year- 
ling Chinook salmon ages, respectively. If no life history stage is indicated, a mixture of ages were observed. 
Common name 
Scientific name 
2007 
2008 
2009 
2010 
American shad 
Alosa sapidissima 
66.7 
74.5 
76.1 
70.6 
Chinook salmon (j, 0) 
Oncorhynchus tshawytscha 
63.3 
58.2 
63.0 
49.0 
Chinook salmon (j, 1) 
Oncorhynchus tshawytscha 
41.7 
52.7 
58.7 
49.0 
Chinook salmon (a) 
Oncorhynchus tshawytscha 
3.3 
0.0 
0.0 
0.0 
Chum salmon (j) 
Oncorhynchus beta 
15.0 
23.6 
21.7 
23.5 
Coho salmon (j) 
Oncorhynchus kisutch 
45.0 
40.0 
47.8 
37.3 
Cutthroat trout 
Oncorhynchus clarki 
1.7 
1.8 
0.0 
3.9 
English sole (j) 
Parophrys vetulus 
3.3 
10.9 
6.5 
5.9 
Kelp greenling (j) 
Hexagrammos decagrammus 
1.7 
10.9 
4.3 
0.0 
Lingcod (j) 
Ophiodon elongatus 
1.7 
5.5 
0.0 
0.0 
Longfin smelt 
Spirinchus thaleichthys 
16.7 
16.4 
23.9 
7.8 
Northern anchovy 
Engraulis mordax 
25.0 
10.9 
15.2 
31.4 
Pacific herring 
Clupea pallasii 
61.7 
30.9 
50.0 
31.4 
Pacific lamprey (a) 
Lampetra tridentata 
0.0 
0.0 
4.3 
0.0 
Pacific sand lance 
Ammodytes hexapterus 
0.0 
1.8 
0.0 
0.0 
Pacific sardine 
Sard inops sagax 
3.3 
0.0 
0.0 
9.8 
Pacific staghorn sculpin 
Leptocottus armatus 
1.7 
0.0 
13.0 
3.9 
Pacific tomcod (j) 
Microgadus proximus 
0.0 
5.5 
0.0 
0.0 
River lamprey (j) 
Lampetra ayresii 
3.3 
5.5 
0.0 
11.8 
Saddleback gunnel 
Pholis ornata 
1.7 
3.6 
2.2 
2.0 
Sand sole (j) 
Psettichthys melanostictus 
1.7 
0.0 
2.2 
0.0 
Shiner perch 
Cymatogaster aggregata 
30.0 
45.5 
47.0 
21.6 
Snake prickleback 
Lumpenus sagitta 
0.0 
0.0 
4.3 
0.0 
Sockeye salmon (j) 
Oncorhynchus nerka 
13.3 
5.5 
4.3 
17.6 
Sockeye salmon (a) 
Oncorhynchus nerka 
0.0 
0.0 
0.0 
2.0 
Starry flounder 
Platichthys stellatus 
1.7 
3.6 
0.0 
5.9 
Steelhead (j) 
Oncorhynchus mykiss 
35.0 
34.5 
52.2 
56.9 
Steelhead (a) 
Oncorhynchus mykiss 
3.3 
0.0 
2.2 
2.0 
Surf smelt 
Hypomesus pretiosus 
86.7 
83.6 
82.6 
86.3 
Threespine stickleback 
Gasterosteus aculeatus 
81.7 
87.3 
91.3 
82.4 
Whitebait smelt 
Allosmerus elongatus 
0.0 
1.8 
0.0 
0.0 
anchovy (especially in 2007 and 2010), Pacific herring 
(2007 and 2009), surf smelt (2008 and 2009), American 
shad (2008), and threespine stickleback (2008-10). This 
pattern of high relative abundance in particular years 
was associated with high absolute abundances of north- 
ern anchovy, Pacific herring, and surf smelt (Fig. 2), 
whereas variable abundances of threespine stickleback 
and American shad occurred despite consistent absolute 
abundances among years (Table 3). Juvenile salmonids 
were typically minor members of the estuarine assem- 
blage (contributing <5% numerically), except in early 
May 2010 (cruise 10-3), when their contribution reached 
39% of all fish caught. As with threespine stickleback 
and American shad, their absolute abundances were 
quite consistent among years. 
Multivariate assemblage analyses Results of the mul- 
tivariate assemblage analyses were consistent with the 
patterns described above: they indicated high variability 
at fine temporal scales (among hauls), and less variabil- 
ity at larger temporal scales (among cruises) or at spatial 
scales (between stations). For example, comparisons 
of specific subsets of pairwise Bray-Curtis similarity 
coefficients based on tidal stage or sampling station 
indicated that the fish assemblage of the Columbia 
River estuary was extremely dynamic at fine temporal 
scales (hours) and less dynamic in space. In particular, 
pairwise similarities calculated among hauls made at 
the same station and on the same day (311 comparisons) 
exhibited nearly as much variation (range: 0- 89.3%) as 
we saw between any 2 hauls across the entire 4 years 
of study (range: 0-98.8%). Furthermore, similarity coef- 
ficients were highest for hauls made close together in 
time (relative to low tide) and declined with increasing 
time between hauls. Specifically, mean pairwise simi- 
larities among hauls conducted within 1 h of each other 
(mean=64.0%), were greater than similarities for hauls 
occurring 1-2 h apart (61.3%), with the lowest mean 
