66 
Fishery Bulletin 1 1 7(1-2) 
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190 200 210 
Predicted length (mm) 
Figure 4 
(A) Observed length at age for female (gray dots) and male 
(black plus signs) blueback herring (Alosa aestivalis) captured 
in the Potomac River in 2007 and 2008 and from 2011 through 
2015, with predicted length at age from von Bertalanffy growth 
models (solid lines). (B) Standardized residuals versus fitted val¬ 
ues for the von Bertalanffy growth curves for female (gray dots) 
and male (black plus signs) blueback herring. 
X 2 =5, df=2, P=0.01). When a Bonferroni adjustment 
was used, the critical P-value became 0.007. With this 
new P-value, only testing the whole model for each sex 
was still statistically different, indicating that the dif¬ 
ferences between the sexes were not a coincidence but 
that none of the model parameters explain the differ¬ 
ences by themselves. 
Discussion 
Females grew faster and larger than males for both 
species of river herring. Similar to the outcome of this 
study, previous studies have documented larger and 
faster-growing females for both species (Marcy, 1969; 
Loesch and Lund, 1977; Loesch, 1987). Additionally, 
alewife grew faster and larger than blueback herring, 
a finding that also has been documented by previous 
studies (Netzel and Stanek, 1966; Messieh, 1977; Jones 
et al., 1978; Fay et al. 1 ; Klauda et al., 1991). In the 
Saint John River in New Brunswick, Canada, female 
alewife grew fastest and largest, followed by 
male alewife, then female blueback herring 
and male blueback herring. However, in the 
Albemarle Sound, North Carolina, female blue- 
back herring grew faster and larger than male 
alewife. Fay et al. 1 provided average length-at- 
age data from multiples studies, information 
that indicates that growth rates of alewife and 
blueback herring were not consistent between 
studies (Fay et al. 1 ). For example, in Georges 
Bank, alewife had a larger average length at 
age than blueback herring for every age, but 
in the Connecticut River larger average length 
varied between these species on the basis of 
age (Netzel and Stanek, 1966; Marcy, 1969; Fay 
et al. 1 ). Why these differences in growth rates 
occurred between these studies is unclear. It 
could be due to differences in geography or 
time, given that both have been documented 
to affect growth of fish populations. 
The estimates of for alewife (273.9 mm 
FL) and for blueback herring (267.0-mm-FL) 
from this study are smaller than previously 
published estimates from other studies. The 
NOAA Northeast Fisheries Science Center 
conducted a bottom-trawl survey from 1973 
through 1987 and used the survey data to es¬ 
timate L„: 282.6 mm FL for alewife and 267.0 
mm FL for blueback herring (ASMFC, 2012). 
For both sexes, the L„ also was smaller for 
individuals examined in this study than for 
individuals captured in the Saint John River 
in New Brunswick (male and female alewife: 
292 and 310 mm FL; male and female blue- 
back herring: 231 and 260 mm FL; Messieh 
1977) and in New Hampshire rivers (male and 
female alewife: 305 and 322 mm TL; male and 
female blueback herring: 287 and 328 mm TL; 
ASMFC, 2012). The differences between esti¬ 
mates of L x were most likely due to a lack of older 
individuals captured in the Potomac River, a situation 
that can lead to a poor estimation of the L„ (Hilborn 
and Walters, 1992). 
Alewife and blueback herring historically have been 
aged up to 14 and 9 years, respectively (ASMFC, 2012), 
but the maximum ages for these species in this study 
were 7 and 6 years. A lack of representation of older 
fish in a data set can result from high adult mortal¬ 
ity rates, gear selectivity, or underaging of fish (Fran¬ 
cis, 1988). High adult mortalities in river herring have 
been linked to increased stress during spawning mi¬ 
grations, historical overfishing practices, and current 
bycatch of adult fish (Hightower et al., 1996; Greene 
et al. 2 ; ASMFC, 2012). This pattern has been seen for 
other adult anadromous fishes as well (Dunton et al., 
2015). The current moratoria for river herring have 
been in effect regionally only for 3 years; therefore, 
older river herring have been protected for a limited 
part of their life span. 
The K value was lower for alewife and male blue- 
