Hurst and Conover: Diet and consumption rates of Morone saxatilis in the Hudson River 
547 
Table 1 
Summary of collections and diets of overwintering YOY striped bass collected in the Hudson River Estuary, 1993-97. %F = mean 
frequency of occurrence, %W = mean percentage of wet weight; n = number of fish sampled per date. 
Winter 
1993 
1994 
1995 
1996 
1997 
No. of dates sampled 
1 
8 
7 
6 
4 
L 
Temperature (°C) 
2.0- 
-5.1 
4.2- 
-10.4 
1.0-9. 4 
3. 3-6. 2 
5.0- 
-6.1 
n 
20- 
-34 
15- 
-53 
8-37 
16-29 
18- 
-52 
Percentage empty stomachs 
71.0 
52.5 
72.3 
57.6 
73.4 
Mean gut fullness ±SE 
0.44 ±0.103 
0.51 ± 
0.056 
0.34 ±0.066 
0.18 ±0.037 
0.26 ± 
o 
o 
a 
o 
Prey type 
Scientific name 
%F 
%W 
%F 
%W 
%F %W 
%F %W 
%F 
%w 
Amphipods 
Gammarus sp. 
66.7 
59.1 
92.1 
90.2 
58.2 39.5 
86.3 52.4 
34.3 
15.7 
Sand shrimp 
Crangon septimspinosa 
37.0 
27.1 
4.2 
4.2 
7.1 8.1 
0 0 
3.1 
5.3 
Grass shrimp 
Palaemonetes pugio, 
Palaemonetes vulgaris 
38.9 
6.4 
0 
0 
4.3 4.1 
0 0 
3.1 
7.5 
Mysid shrimp 
0 
0 
0 
0 
0 0 
3.0 7.1 
18.8 
4.3 
Unidentifiable 
C. septimspinosa, 
0 
0 
0.7 
0.4 
27.5 22.8 
16.4 32.5 
21.4 
26.4 
shrimp 
Crabs 
P. pugio, P. vulgaris 
33.3 
5.7 
0 
0 
0 0 
0 0 
0 
0 
Polychaetes 
0 
0 
0 
0 
17.9 23.3 
0 0 
0 
0 
Oligochaetes 
0 
0 
0 
0 
0 0 
0 0 
23.9 
38.8 
Fish 
Anchoa mitchilli, 
Menidia menidia, 
Ammodytes americanus 
1.9 
1.7 
5.4 
5.3 
2.9 2.2 
7.1 8.0 
3.1 
1.9 
UIR 7 
40.7 
24.4 
11.9 
8.5 
28.2 6.0 
31.8 29.2 
42.2 
25.1 
1 UIR = unidentified invertebrate remains. These were not included in the calculation of %W of other prey items. 
c 0 and c x = the intercept and slope of the linear relation- 
ship between temperature and the lag prior 
to the beginning of evacuation. 
If no lag is present in the data, the parameters c 0 and Cj 
approach 0. The effect of body size on evacuation was as- 
sessed by examining the relationship between fish length 
and deviation from the best fitting evacuation model. 
Diet of YOY striped bass 
Overwintering YOY striped bass were collected with a 9-m 
bottom trawl (38-mm stretch mesh codend) from the lower 
Hudson River estuary, the only known wintering aggre- 
gation for the Hudson River population (Dovel, 1992). 
Sampling occurred throughout the overwintering period 
of five consecutive years. Fish were captured during day- 
light hours between river mile 0 and 9 in conjunction with 
the New York Power Authority’s hatchery evaluation and 
tagging program. Sampling in each year began in mid- 
December and ended in late March or early April. Bottom 
water temperatures were measured during sampling. The 
number of fish analyzed for diet per date ranged from 8 
to 53 depending on catch rates (Table 1). Captured fish 
were individually wrapped and immediately frozen for 
preservation. In the laboratory, fish were thawed, mea- 
sured (mm TL), weighed (g wet weight), and stomach con- 
tents were removed. Prey were identified to the lowest 
possible taxon and weighed. All prey in each category in 
each stomach were weighed as a group because the abun- 
dance and small size of the dominant prey item made 
individual measurements unfeasible (gammarid amphi- 
pods; often >50/stomach and <0.005 g each). Diets of YOY 
striped bass were described by the contribution of items 
expressed on the basis of both weight (%W —weight of prey - 
/weight of all identifiable prey ) and frequency (%F = 100 
x no. of stomachs with prey J no. of stomachs with prey). 
Unidentifiable items were measured separately and are 
expressed as a percentage of the total weight of all stom- 
ach contents. 
Estimation of consumption rates 
Daily consumption rate estimates were generated by com- 
bining gut fullness values (S=total weight of stomach 
contents/fish weight) of overwintering YOY striped bass 
with laboratory-determined gastric evacuation rates with 
the method of Eggers (1979): 
C = 24 R, x S, 
