Hurst and Conover: Diet and consumption rates of Morone saxotilis in the Hudson River 
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co 
05 
05 
CD 
(3 
2 - 
0 - 
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* * 
JS. 4 *. t . 
10 15 20 25 
Lipid level (% dry weight) 
30 
35 
Figure 3 
Relationship between gut fullness and lipid level of overwintering 
YOY striped bass through five winters. Points are gut fullness and 
lipid levels of individual fish. 
Q 
co 
+i 
1 Jan 
1 Feb 
Date 
1 Apr 
Figure 4 
Relationship between mean gut fullness (±1 SE) observed on a 
given date and date for collections of YOY striped bass through five 
winters. 
the total evacuation time, averaging only 11% of 
the time required to reach 75% digestion. Sim- 
ulations that varied the length of the digestive 
lag time and the evacuation rate showed that 
for lag times in the range we observed, consump- 
tion rates were overestimated by less than 5%. 
If the lag observed in the laboratory experiments 
does not occur in the wild, estimated consump- 
tion rates are unbiased. 
Diet 
Diets of overwintering YOY striped bass in the 
lower Hudson River estuary were dominated by 
benthic invertebrates such as gammarid amphi- 
pods and several shrimp species. Juvenile striped 
bass do not appear to undergo a major diet 
shift from summer to winter but appear to focus 
more heavily on amphipods in winter. Studies 
of summer diets of striped bass in the Hudson 
River from the 1970s and 1990s found a slightly 
more diverse diet than we observed in winter. 
Summer diets included copepods, chironomids, 
and isopods, and more commonly incorporated 
fish and polychaetes (Gardinier and Hoff, 1982; 
Hurst, unpubl. data). Data from other estuaries 
suggest that the diets of overwintering juvenile 
striped bass may vary regionally. In Chesapeake 
Bay, Hartman and Brandt (1995a) found that 
fish prey accounted for 20-25%W of YOY striped 
bass diets in winter, substantially more than the 
2-9%W we observed in the Hudson River. In the 
Miramichi River estuary, overwintering fish fed 
primarily on shrimp (mysids and C. septemspi- 
nosa) and ceased feeding when temperatures fell 
below 3°C in late November (Robichaud-LeBlanc 
et al., 1997). The studies from Chesapeake Bay 
and the Miramichi River estuary did not examine 
interannual variability in diets. 
Overwintering juvenile striped bass appear to 
be opportunistic feeders, their diets reflective of 
the epibenthic invertebrate community in the low- 
er Hudson River and similar to published informa- 
tion on the diets of co-occurring species. Although 
there have been no surveys of the benthic com- 
munity in the lower Hudson River in winter, data 
available from summer surveys in the Hudson 
River estuary and the adjacent Raritan estuary 
suggest dominance of the epibenthic community 
by gammarid amphipods, shrimp, and annelids 
(Ristich et al., 1977; Steimle and Caracciolo-Ward, 1989). 
The winter fish community in the lower Hudson River is 
composed primarily of striped bass, white perch, Atlantic 
tomcod (Microgadus tomcod), and winter flounder (Pseudo- 
pleuronectes americanus). Winter diets of Atlantic tomcod 
were dominated by gammarid amphipods and copepods 
and were significantly less diverse in winter than in spring 
and autumn (Grabe, 1977, 1980). Diets of age-1 and older 
striped bass overwintering in the lower Hudson River estu- 
ary are similar to those of YOY fish, although the incidence 
of juvenile fish prey (including YOY striped bass) increased 
with body size (Dunning et al., 1997). 
Consumption rates 
Consumption estimates of overwintering YOY striped bass 
in the Hudson River were consistently below l%bw/day, 
with only 34% of captured fish containing prey items. 
Our field estimates of the consumption rates of over- 
wintering striped bass are significantly lower than pub- 
