Hurst and Conover: Diet and consumption rates of Morone saxatilis in the Hudson River 
549 
tr 
Hours since ingestion 
Figure I 
Gastric evacuation patterns of YOY striped bass fed Crangon septemspinosa at four tem- 
peratures. Points are observations of percentage of initial meal remaining in the stomach 
after a predetermined time. Lines represent evacuation model fitted by using all data. 
Diet composition 
Benthic invertebrates were the dominant prey of YOY 
striped bass overwintering in the lower Hudson River estu- 
ary, making up 95.0% of the diet by weight; the remaining 
5.0% were various fish prey (Table 1). Most striped bass 
captured during winter had empty stomachs (64.8%), and 
on two dates, all fish sampled had empty stomachs (30 
March 1994 and 6 December 1994). Unidentifiable stomach 
contents ranged from 6.0% weight (%W) in 1995 to 29.2%W 
in 1996. The most common item in the diet was gammarid 
amphipods (those identified to genus were Gammarus sp., 
but most were not identified) making up 51.3%W and 
occurring in 81% of stomachs with food (%F). Several spe- 
cies of shrimp were also common dietary items, including 
sand shrimp (C. septemspinosa ) and grass shrimps (Palae- 
monetes spp.). Other invertebrates that were important 
items on several dates included mysid shrimp, polychaetes, 
and oligochaetes. Fish were rarely found in the stomachs 
of YOY striped bass (3.8%F) but included bay anchovy 
(Anchoa mitchilli), Atlantic silversides (Menidia menidia ), 
and American sand lance (Ammodytes americanus ). 
The importance of individual prey taxa varied among 
years and among dates within each year, although low 
sample sizes of fish with prey prevent drawing strong 
conclusions from these data. In 1994, striped bass fed al- 
most exclusively on gammarid amphipods (90.2%W and 
92.1%F), but these prey were less important in other 
years. Shrimp were important in 1993 (33.5%W, mostly C. 
septemspinosa) and 1995-97 (34.9 to 43.6%W all species). 
Polychaetes were observed in striped bass diets only in 
1995 (23.3%W and 17.9%F). Oligochaetes were found com- 
monly in 1997, averaging 18.5%F and 23.9%W of the diet 
but did not occur in other years. 
Consumption rates 
Assuming an exponential evacuation pattern, consumption 
rate estimates for overwintering YOY striped bass ranged 
from 0 to 0.29% body weight per day (%bw/day, Fig. 2). Stan- 
dard deviations of estimated consumption averaged 46% 
of the estimate (range: 20.2-100.9%). The standard devi- 
ation of the consumption estimate was relatively insensi- 
tive to assumptions of the covariance between S and R e . 
The ratio of estimates under the least conservative assump- 
tion (perfect covariance) to that under the most conserva- 
tive assumption (perfect negative covariance) was less than 
1.08, with one exception (1.17 on 20 December 1993). The 
standard deviations presented in Figure 2 are the interme- 
diate values, based on the assumption of no covariance. 
Feeding patterns 
Among individuals, we observed a strong negative relation- 
ship between maximum gut fullness and the level of stor- 
age lipids. The 95 th quantile of gut fullness was 3% for fish 
with lipid reserves of 2% dry weight and decreased to under 
1% for fish with lipid levels in excess of 19%< dry weight 
(Fig. 3). No significant patterns were observed between 
individual gut fullness levels and water temperature, time 
