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Fishery Bulletin 95(4), 1997 
Locations where beach seines and gill nets were used at Croton Point, 
New York, in the lower Hudson River estuary. 
atilis, and American shad, Alosa sapidissima 
(Juanes et al., 1993; 1994). Mortality caused 
by YOY bluefish predation may be intense 
given the relatively high consumption rates 
of this species (Juanes and Conover, 1994; 
Buckel et al., 1995). In order to assess the 
effect of YOY bluefish predation, an under- 
standing of the location and timing of blue- 
fish prey interactions, as well as accurate and 
fine-scale temporal measurements of bluefish 
consumption rates, are needed. 
Consumption rates of fish are measured 
with direct methods (laboratory- or field- 
based) and indirect methods. The field-based 
method requires measurements of gut full- 
ness over a diel cycle coupled with estimates 
of gastric evacuation rate (Elliott and 
Persson, 1978; Eggers, 1979). The indirect 
method most widely used is a bioenergetic 
approach that requires knowledge of the 
predator’s growth trajectory, physiological 
parameters, and environmental data (Kit- 
chell et al, 1977). Because all of these meth- 
ods have their drawbacks and their use is 
controversial (Hewett et al., 1991; Boisclair 
and Leggett, 1991), we used a combination 
of different techniques in order to compare 
methods and cross-validate results. 
Juanes and Conover ( 1994) and Buckel et 
al. (1995) measured YOY bluefish consump- 
tion rates in the laboratory. Steinberg (1994) 
estimated daily ration of Hudson River YOY 
bluefish with a bioenergetics modeling ap- 
proach. However, the only two field estimates of blue- 
fish consumption rates that exist were made in Great 
South Bay, NY (Juanes and Conover, 1994), an envi- 
ronment that differs from the Hudson River estuary. 
Here we report on the results of diel field collec- 
tions of YOY bluefish during the summers of 1992 
and 1993 in the Hudson River estuary. These collec- 
tions allowed us to determine temporal and spatial 
(e.g. inshore vs. offshore) patterns of YOY bluefish 
movements and feeding. Gut-fullness values were 
coupled with previously determined estimates of 
gastric evacuation rates (Buckel and Conover, 1996) 
to estimate YOY bluefish daily ration. 
Methods 
Die! coHections — beach seine 
Spring- and summer-spawned YOY bluefish (cohorts 
easily identified by size) and their prey were collected 
from the lower Hudson River estuary in 1992 and 
1993 on the north shore of Croton Point (41 0 ll'N, 
73°54'W; Fig. 1). Ten diel beach-seine collections were 
made: five in 1992 (16-17 July, 28-29 July, 13-14 
August, 26-27 August, and 19-20 September) and 
five in 1993 (7-8 July, 20-21 July, 4-5 August, 18— 
19 August, and 11-12 September). Collections were 
made every three hours beginning at 1200 h and 
ending at 1200 h the following day. Sampling began 
30 min before and ended 30 min after each time point 
(e.g. sampling for the 1200 time point began at 1130 
and ended at 1230). A 60 x 3 m beach seine (13-mm- 
mesh wings, 6-mm-mesh bag) and a 30 x 2 m beach 
seine (6-mm-mesh wings, 3-mm-mesh bag) were used 
for nearshore sampling. The 60-m seine was set by 
boat. A minimum of two 60-m seine hauls were made 
during each one-hour sampling period. Additional 
seine hauls were sometimes made to increase blue- 
fish sample size. Bluefish and samples of prey were 
immediately preserved in 10% formalin. Catch-per- 
unit-of-effort (CPUE) of bluefish was calculated as 
the number of fish caught per seine haul in the first 
two 60-m seine hauls. Potential prey were counted 
