Weitkamp et al.: Seasonal and interannual variation in juvenile salmonids in the lower Columbia River 
431 
Table t 
Sampling effort, regional river flow, and river temperature by year and cruise during the 4 years (2007-10) of our study of the 
estuarine ecology of juvenile salmonids and their associated fish assemblage in open-water habitats of the lower Columbia River 
estuary. Sampling effort totals, measured as the total number of hauls (round and towed) completed, are provided with dates of 
each cruise. 
Total 
no. of hauls 
Mean river flow 
Mean river temperature 
Year 
Cruise no. 
Dates 
(no. of round hauls) 
(1000 m 3 /sec) 
(°C) 
2007 
7-1 
17-18 April 
8(8) 
8.0 
9.3 
7-2 
1-4 May 
24 (16) 
8.7 
11.3 
7-3 
15-17 May 
13 (9) 
9.0 
13.3 
7-4 
30-31 May 
14(11) 
7.8 
15.0 
7-5 
12-13 June 
13 (10) 
7.9 
16.0 
7-6 
27-28 June 
2007 effort 
7 (6) 
79 (60) 
5.7 
17.5 
2008 
8-1 
10 April 
3(3) 
6.1 
7.2 
8-2 
23-24 April 
12 (6) 
7.6 
9.0 
8-3 
6-8 May 
18(12) 
8.3 
11.0 
8-4 
20 May 
7 (6) 
13.5 
13.5 
8-5 
3-5 June 
15(9) 
13.9 
13.5 
8-6 
18-19 June 
14(8) 
12.5 
14.9 
8-7 
30 June-1 July 
2008 effort 
11 (10) 
80(54) 
11.1 
17.1 
2009 
9-1 
15 April 
3(3) 
9.3 
8.5 
9-2 
23-24 April 
15 (9) 
9.9 
9.7 
9-3 
7-8 May 
13(10) 
11.2 
10.3 
9-4 
21-22 May 
10(8) 
11.1 
13.3 
9-5 
4-5 June 
13 (9) 
11.3 
15.4 
9-6 
23-24 June 
2009 effort 
8(7) 
62(46) 
8.2 
17.1 
2010 
10-1 
13-14 April 
14(9) 
7.9 
9.3 
10-2 
28-29 April 
12 (6) 
7.7 
11.5 
10-3 
11-12 May 
10(10) 
7.4 
11.9 
10-4 
25-26 May 
9(7) 
8.8 
13.3 
10-5 
8-9 June 
12 (6) 
13.4 
14.4 
10-6 
23-24 June 
2010 effort 
13 (12) 
70 (50) 
11.6 
15.6 
especially Chinook and coho salmon and steelhead, were 
more detailed than our analyses of other fishes. 
Fish abundance and composition Analysis of temporal 
and spatial variation of the estuarine fish assemblage 
was restricted to catch data collected from round hauls 
(n=210). Seasonal changes in abundance for each of 6 
juvenile salmon species-and-age classes (subyearling 
and yearling Chinook, coho, sockeye, and chum salmon 
and steelhead) were qualitatively assessed by visually 
comparing mean CPUE per cruise by year. 
For the entire fish assemblage, including juvenile 
salmon, we calculated the following univariate metrics 
to assess patterns of abundance: 1) frequency of oc- 
currence of all fish species during each year, 2) mean 
CPUE and coefficients of variation for the most com- 
monly caught species, and 3) total abundance of all fish- 
es and the relative abundance (as percentage of total) of 
the most commonly caught fishes, averaged by cruise. 
Data generated from these analyses were visually com- 
pared. These qualitative measures complemented mul- 
tivariate techniques, specifically: 1) direct comparisons 
of subsets of Bray-Curtis similarity coefficients among 
hauls to examine fine-scale temporal and spatial influ- 
ence, 2) nonmetric multidimensional scaling (MDS) by 
haul and cruise, and 3) analysis of similarities (ANO- 
SIM, a multivariate analog for analysis of variance, 
ANOVA) to test for the influence of temporal variation. 
All multivariate analyses were run with PRIMER-E 6 
software (PRIMER-E Ltd., vers. 6, Ivybridge, U.K.). 
6 Mention of trade names or commercial companies is for 
identification purposes only and does not imply endorsement 
by the National Marine Fisheries Service, NOAA. 
