Weitkamp et al.: Seasonal and interannual variation in juvenile salmonids in the lower Columbia River 
441 
300.0; 
250. o: 
200 Oj 
150 o: 
100 o: 
50 0- 
0 . 0 - 
Yearling Chinook 
189 168 225 382 
2007 2008 2009 2010 
150.0; 
125.0; 
100 . 0 ; 
75 . 0 ; 
5o.o; 
25.0; 
0 . 0 - 
Subyearling Chinook 
if 
♦ 
615 357 465 515 
225. 0g 
200 . 0 : 
175 0; 
150.0: 
sz 
125.0; 
0 
100 . 0 ; 
75.0; 
50. o; 
25.0; 
0 Q: - 
Coho salmon 
♦ 
319 185 232 206 
2007 2008 2009 2010 
350 0; 
300.0; 
250. o; 
200 0 ; 
150 . 0 ; 
ioo o; 
50 o; 
0 o: 
Steelhead 
2007 2008 2003 2010 
125 0 
100 0 
75 0 
50.0 
25.0- 
0 0 
Chum salmon 
Figure 6 
Box plots of fork length (mm) by year for each juvenile salmon species-and-age 
class: yearling and subyearling Chinook salmon (Oncorhynchus tshawytscha), coho 
salmon ( O . kisutch ), steelhead (O. mykiss), chum salmon (O. keta), and sockeye 
salmon ( O . nerka). The box plots illustrate 25 th and 75 th percentiles (lower and 
upper edges of box, respectively), the median (line within the box), 10 th and 90 th 
percentiles (whiskers [error bars] below and above the box), and dots indicate 
outliers (<10 th or >90 th percentiles). Samples sizes are provided below each box. 
Scales for each graph are different to emphasize species-specific patterns. 
events served as natural experiments for the influence 
of flow. High flow rates influence water column proper- 
ties and circulation patterns in the estuary (Jay and 
Smith, 1990; Chawla et al., 2008), including the decline 
of maximum surface salinity that we observed with in- 
creasing flows. Estimated residence time of water in the 
Columbia River estuary also was much shorter during 
high flows in 2008 than in 2007, 2009, or 2010 (CCMOP, 
2010). High flows also may cause direct, species-specific 
behavioral responses in fish, including downstream 
displacement (Dege and Brown, 2004; Purtlebaugh and 
Allen, 2010). Northern anchovies seem particularly 
sensitive to high river flows as indicated by their near 
absence when flows were high in 2008 (cruise 8-4 in 
