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Fishery Bulletin 95(4), 1997 
Table 2 
Stomach contents of spring-spawned bluefish, Pomatomus saltatrix, captured during diel beach-seine collections in the Hudson 
River estuary in 1993. %F = frequency of occurence, %W = percent wet weight. 
Prey type 
Date 
7-8 July 
20-21 July 
4-5 Aug 
11-12 Aug' 
18-19 Aug 
11-12 Sept' 
Total 
Species 
Common name 
%F 
%W 
%F %W 
%F 
1 %W 
%F %W 
%F 
%W 
%F 
%W 
%F 
%W 
Anchoa mitchilli 
bay anchovy 
27.9 
13.5 
30.2 27.3 
15.1 
8.9 
15.4 5.9 
12.2 
7.8 
12.5 
3.2 
21.7 
9.9 
Morone saxatilis 
striped bass 
32.0 
67.8 
17.4 41.2 
16.3 
37.0 
7.7 13.8 
13.0 
28.9 
12.5 
23.9 
20.7 
32.2 
Alosa sapidissima 
American shad 
2.3 
8.5 
1.0 
1.4 
0.6 
2.4 
Alosa spp. 
2.3 5.8 
5.8 
5.0 
2.6 0.5 
4.1 
4.0 
2.5 
3.3 
Menidia menidia 
Atlantic silverside 
1.2 
1.2 
1.2 2.5 
16.3 
23.1 
41.0 69.7 
22.5 
35.9 
12.5 
21.0 
11.5 
32.8 
Other fish 2 
3.5 
1.7 
4.1 
9.0 
12.5 
13.2 
3.4 
4.3 
Unidentified fish 
remains 
40.1 
14.8 
48.8 21.8 
40.7 
10.8 
25.6 7.5 
45.0 
12.0 
75.0 
37.1 
42.1 
13.2 
Total Fish 
97.3 
98.6 
95.0 
97.4 
99.0 
98.4 
98.0 
Crangon and 
sand and 
Palaemonetes spp. 
grass shrimp 
14.0 
4.6 
10.3 2.6 
3.1 
0.3 
12.5 
1.6 
4.1 
1.6 
Zoeae and copepods 
6.4 
2.4 
1.2 0.2 
2.0 
0.4 
Other 3 
5.2 
0.3 
11.0 1.2 
7.0 
0.4 
10.2 
0.3 
7.0 
0.4 
Total stomachs analyzed 
248 
137 
119 
47 
129 
23 
703 
Number containing prey 
172 
86 
86 
39 
98 
8 
489 
Mean bluefish size (g) (SE) 
4.96 
8.96 
19.84 
23.29 
33.41 
75.67 
(0.10) 
(0.51) 
(0.94) 
(1.41) 
(1.59) 
(8.79) 
1 Bluefish that were captured on 11-12 Aug and 11-12 September were not used to calculate daily ration. 
2 “Other fish” includes killifish, Fund ulus spp., American eel, Anguilla rostrata, white perch, Morone americana, Morone spp., Atlantic menhaden, 
and unidentifiable sciaenids. 
3 “Other” includes vegetation, gravel, sand, and rope fibers. 
may leave an area of high bluefish densities. How- 
ever, we found no evidence of a correlation between 
prey and predator abundance; although positive re- 
lations between bluefish and prey abundance were 
found on three out of four dates in 1993, these corre- 
lations were nonsignificant. 
Sea-surface illumination was the only environmen- 
tal factor describing a significant amount of the varia- 
tion in nearshore CPUE of YOY bluefish. Young-of- 
the-year fish of several shallow-water marine fishes 
move inshore at night (Keats, 1990; Burrows et al., 
1994). We, however, observed an opposite pattern for 
bluefish in our study. Given that bluefish are visual 
predators, diurnal schooling and foraging in the 
nearshore zone is a possible explanation for relatively 
high and variable daytime beach-seine CPUE. Olla 
and Studholme (1972) found that adult bluefish in 
the laboratory had higher activity (swimming speed) 
and a larger schooling group size during the day than 
at night. The difference in diel activity was also seen in 
YOY bluefish and shown to be endogenous (Olla and 
Studholme, 1978). Olla and Marchioni ( 1968) found that 
photomechanical changes in the retina of YOY blue- 
fish were also internally controlled and thus lessened 
the time required for light and dark adaptation. Such 
diurnal rhythms would offer a selective advantage for 
a predator dependent on vision for prey capture. 
Feeding period 
During 1992 and 1993, gut-fullness values from blue- 
fish caught in beach seines were highest during day, 
evening, and morning collections. However, there 
were dates in 1993 when bluefish gut-fullness levels 
indicated nocturnal feeding; these dates occurred 
with a recent full moon (7-8 July, 4-5 August) and a 
new moon (20-21 July). Therefore, moonlight is not 
entirely responsible for the nocturnal feeding seen 
in 1993. In laboratory tanks, YOY bluefish are ca- 
pable of feeding in complete darkness (Juanes and 
Conover, 1994). Tide may also influence the timing 
of feeding; however, the timing of low and high tide 
had no consistent influence on peaks in gut-fullness 
levels (Fig. 3-4). 
