Pearcy and Fisher: Ocean distribution of Alosa sapidissima along the Pacific coast of North America. 
449 
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Latitude (°N) 
B 
150 170 190 210 230 250 270 
Day of year 
Figure 6 
Trends in weight of American shad (Alosa sapidissima) 
by (A) latitude, and (B) day of year during the 1977-2004 
Alaska Fisheries Science Center triennial surveys. Boxes 
span the 25th to 75th percentiles. The line and cross 
within each box indicate the median and mean weight, 
respectively. The whiskers indicate the minimum and 
maximum weights, except when outliers are present at 
more than 1.5 interquartile ranges (box heights) above 
or below the box. Small squares indicate outliers and 
small squares with crosses extreme outliers. 
where SSTs were between 13° and 17°C and bottom tem- 
peratures were usually between 6.4° and 8°C. Neves and 
Depres (1979) caught Atlantic shad at SSTs of 2-23°C 
but concluded that bottom temperatures of 3-15°C pro- 
vided a better basis for predicting movements of Atlantic 
shad in the ocean during all seasons of the year. 
These differences in distributional and migration pat- 
terns of Pacific and Atlantic American shad are con- 
sistent with the phenotypic plasticity that has allowed 
adaptations to the unique environmental conditions 
along the Pacific coast over the past 100 years (see 
also Petersen et al., 2003). Rottiers et al. (1992) found 
that juvenile shad from the Columbia River had higher 
growth rates than did shad from the Delaware River 
and that the two stocks differed genetically. Quinn and 
Adams (1996) concluded that shad in the Columbia Riv- 
0.9 1 t 
0.8 
0.7 
0.6 
0.5 
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0.3 
i 1 H 
o> 1975 1980 1985 1990 1995 2000 2005 2010 
l 0.9 
0.8 
0.7 
0.6 
0.5 
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0.3 
B 
'{I 
1975 1980 1985 1990 1995 2000 2005 2010 
Year 
Figure 7 
Mean weight (±2 standard errors) of American shad 
(Alosa sapidissima ) by year during the 1977-2004 
Alaska Fisheries Science Center triennial (black) and 
the 2003-08 Northwest Fisheries Science Center (gray) 
surveys: (A) uncorrected for date or depth of capture, 
and (B) results of a general linear model applied to 
both surveys combined where weight is the response 
variable, year is the categorical variable, and depth 
and day of year are quantitative variables (r 2 = 0.30). 
In (B) the mean weights are standardized to the aver- 
age depth of 114 m and the average sample day 219 
(August 7). In 2004 weights of shad in both surveys 
were very similar. 
er have evolved a migratory pattern that allows greater 
behavioral response to environmental conditions because 
they now migrate into the river earlier in the year and 
at lower temperatures than during the prior 45 years. 
Future molecular and otolith microchemistry studies 
are needed to determine possible differences among 
spawning runs in different rivers, home stream fidelity, 
and distributional and migratory patterns at sea during 
their ocean migrations along the Pacific coast. 
Counts of shad migrating past Bonneville Dam on the 
Columbia River provide important data on their abun- 
dances and interannual variability. The different indi- 
ces of shad abundance (% FO, average log 10 (caic/z+l), 
and average raw catch) during the AFSC and NWFSC 
demersal sampling on the shelf (<200 m) between 44°N 
