545 
Abstract— Starvation is often proposed 
as the mechanism of size-dependent 
mortality of overwintering temperate 
fishes, yet little is known about the 
energetics of fish at low temperatures. 
Young-of-the-year (YOY) Hudson River 
striped bass ( Morone saxatilis) suffer 
a winter energy deficit and experience 
size-selective winter mortality in some 
years that may influence recruitment. 
To better understand the role of ener- 
getic stress in winter mortality, we 
determined diet composition and mea- 
sured consumption rates of wild fish. 
Gastric evacuation rates were mea- 
sured in the laboratory at 2°, 5°, 8°, 
and 11°C. Measured evacuation rates 
for YOY striped bass were among the 
lowest reported, with 25% of the initial 
meal remaining after 150 hours at 
2°C. Variation in evacuation rate data 
increased as temperature decreased. 
Diets of fish captured in winter were 
dominated by gammarid amphipods 
and shrimp species. Gut fullness ranged 
from 0% to 7%, averaging 0.4% body 
weight. Evacuation rates, gut fullness 
values, and river temperatures were 
combined to estimate daily consump- 
tion rates on 29 dates over five win- 
ters. Consumption estimates ranged 
from 0% to 0.29%bw/day and were gen- 
erally higher in early winter than in 
late winter and not correlated with 
river temperatures. Stomach fullness 
was negatively correlated with the level 
of lipid energy reserves at the indi- 
vidual level. The patterns may reflect 
an internal control on appetite, or a 
depression of prey availability in late 
winter. These findings indicate that the 
potential for winter starvation may be 
influenced by both internal and exter- 
nal constraints on consumption rate. 
Manuscript accepted 15 March 2001. 
Fish. Bull. 99:545-553 (2001) 
Diet and consumption rates of overwintering YOY 
striped bass, Morone saxatilis, in the Hudson River" 
Thomas P. Hurst 
David O. Conover 
Marine Sciences Research Center 
State University of New York 
Stony Brook, New York 11794-5000 
E-mail address (for T P Hurst): hurst@msrc.sunysb edu 
Although the feeding and growth of 
many temperate fish species have been 
extensively examined during summer 
months, details of the feeding ecology 
of most species during winter remain 
largely unknown. Knowledge of the 
winter energetics of many fish species 
is restricted to the observation that 
growth decreases markedly in autumn 
and often becomes negligible during 
winter. There are only scattered reports 
of the feeding patterns of overwin- 
tering temperate fishes (Daiber, 1956; 
Keast, 1968; Foltz and Norden, 1977; 
Diana, 1979), and few estimates of con- 
sumption rates (but see Diana, 1979; 
Minton and McLean, 1982). This lack of 
information on the winter energetics of 
fishes applies also to laboratory-based 
physiological measurements, including 
gastric evacuation rates and metabolic 
rates. Despite the observation that tem- 
perature is the predominant factor reg- 
ulating digestion, for none of the 22 
species listed in a compilation of gas- 
tric evacuation data (He and Wurts- 
baugh, 1993) had rates been measured 
at the minimum temperatures likely to 
be encountered in winter. 
Many temperate fish species lose en- 
ergy throughout the winter, relying up- 
on stored lipid reserves to fuel metabo- 
lism (Toneys and Coble, 1980; Schultz 
and Conover, 1997; Hurst et al., 2000). 
Reliance on lipid reserves is believed 
to be necessary because consumption 
rate is severely limited by the ability 
of fish to digest food at low tempera- 
tures. However low consumption rates 
of overwintering fish may also be limit- 
ed by low food availability (Cunjak and 
Power, 1987; Foy and Paul, 1999). 
Winter mortality that selects against 
smaller fish has been documented in 
a number of temperate species (Sog- 
ard, 1997) and is most commonly at- 
tributed to depletion of lipid energy 
reserves and starvation. Smaller fish 
have higher starvation mortality rates 
because they tend to have lower en- 
ergy reserves and higher weight-spe- 
cific metabolic rates than larger fish. 
An implicit assumption in the “star- 
vation hypothesis” is that overwinter- 
ing fish have little or no capacity to 
obtain energy by feeding. However, in 
several experiments, fish allowed to 
feed ad libitum had higher winter sur- 
vival rates than unfed fish (Post and 
Evans, 1989; Thompson et al., 1991; 
Hurst and Conover, 1998). Although 
wild fish are unlikely to have access 
to unlimited food, these results suggest 
that fish benefit from feeding during 
winter. Furthermore, some overwinter- 
ing fish increase consumption rates in 
response to depletion of internal re- 
serves (Metcalfe and Thorpe, 1992; Bull 
et al., 1996; Hurst and Conover, 2001). 
These findings suggest the need for a 
more complete understanding of the 
energetics of overwintering fish, includ- 
ing consumption rates of wild fish and 
an evaluation of factors that regulate 
consumption in winter. 
The striped bass (Morone saxatilis ) 
is a relatively well studied, commer- 
cially important species along the east 
coast of the United States and Canada 
(Boreman and Austin, 1985). Previous 
work has shown that recruitment to 
the Hudson River population may be 
regulated by the severity of the winter 
that age-0 fish encounter (Hurst and 
Conover, 1998). In addition, size-selec- 
* Contribution 1226 of the Marine Sciences 
Research Center, State University of New 
York, Stony Brook, New York 11794. 
