Buckel and Conover: Movements, feeding, and daily ration of Pomatomus saltatrix 
673 
TabSe 1 
Stomach contents of spring- and summer-spawned bluefish, Pomatomus saltatrix, captured during diel beach-seine collections in 
the Hudson River estuary in 1992. %F = frequency of occurence, %W = percent wet weight. 
Prey type 
Spring-spawned 
Summer- 
spawned 
Spring- 
spawned 
16-17 July 
28-29 July 
13- 
14 Aug. 
26-27 Aug. 
19-20 Sept. 
19-20 Sept. 
Total 
Species 
Common name 
%F 
%W 
%F 
%W 
%F %W 
%F 
%W 
%F 
%W 
%F 
%W 
%F %W 
Anchoa mitchilli 
bay anchovy 
13.5 
11.0 
5.1 
1.9 
3.0 
0.7 
10.3 
1.1 
41.4 
47.1 
19.2 
18.5 
15.0 18.4 
Morone saxatilis 
striped bass 
17.5 
24.4 
5.1 
3.9 
15.2 
23.7 
11.8 
39.0 
4.6 
9.5 
11.8 19.6 
Morone americana 
white perch 
2.4 
1.8 
6.8 
5.6 
6.1 
10.6 
1.5 
1.7 
1.2 
2.6 
3.4 4.8 
Morone spp. 
5.6 
2.3 
3.4 
1.5 
5.1 
4.3 
2.9 
1.9 
1.2 
1.0 
3.9 2.2 
Alosa sapidissima 
American shad 
6.4 
15.6 
15.3 
24.1 
5.1 
7.3 
7.4 
6.6 
9.2 
9.7 
2.1 
9.3 
8.0 10.5 
Alosa aestivalis 
blueback herring 
3.2 
4.9 
15.3 
12.7 
1.0 
1.4 
3.2 2.1 
Alosa pseudoharengus 
alewife 
3.4 
7.1 
1.0 
3.0 
0.7 1.5 
Alosa spp. 
21.4 
22.9 
25.4 
26.1 
18.2 
17.4 
17.7 
8.7 
10.3 
5.4 
14.9 
26.4 
18.5 13.0 
Menidia menidia 
Atlantic silverside 
2.3 
2.3 
7.1 
8.6 
13.2 
13.8 
2.3 
5.2 
2.1 
7.7 
4.8 6.9 
Microgadus tomcod 
Atlantic tomcod 
0.8 
0.4 
1.0 
2.2 
2.9 
13.4 
2.3 
2.5 
1.4 4.0 
Other fish 7 
1.0 
0.1 
1.5 
3.0 
0.4 0.5 
Unidentified fish remains 
38.9 
12.9 
52.5 
16.9 
49.5 
20.5 
41.2 
10.8 
39.1 
14.2 
55.3 
33.6 
43.5 15.3 
Total fish 
98.5 
99.8 
99.8 
99.5 
97.2 
95.5 
98.8 
Crangon spp. 
sand shrimp 
1.5 
0.2 
4.6 
1.0 
8.5 
4.0 
1.1 0.2 
Zoeae and copepods 
0.8 
0.5 
1.7 
<0.1 
2.0 
<0.1 
2.9 
0.3 
1.2 
1.3 
3.6 0.7 
Other 2 
3.4 
0.2 
9.1 
0.2 
1.5 
<0.1 
8.0 
0.5 
14.9 
0.8 
4.9 0.3 
Total stomachs analyzed 
179 
83 
125 
85 
99 
64 
571 
Number containing prey 
126 
59 
99 
68 
87 
47 
439 
Mean bluefish size (g) (SE) 
4.48 
11.30 
25.04 
41.16 
43.71 
10.29 
(0.18) 
(0.69) 
( 
1.27) 
(2.78) 
(2.01) 
(1.29) 
1 “Other fish” include Atlantic menhaden, Brevoortia tyrannus, and bluefish, Pomatomus saltatrix. 
2 “Other” includes vegetation, gravel, sand, and rope fibers. 
water (2. 2-2. 6 m), and deep-water (5. 2-5. 6 m) zones 
of a Florida estuary. Using a subtidal weir in a 
polyhaline marsh creek in New Jersey, Rountree and 
Able (1993) captured a significantly higher number 
of YOY bluefish during day sampling than during 
night sampling. They concluded that this CPUE pat- 
tern was a result of diurnal foraging or increased 
activity (or both). Juanes and Conover (1994) made 
two diel beach-seine collections in Great South Bay, 
NY. Although they made no comparison between 
night and day abundance, their mean diurnal catch 
was two to three times higher than their mean noc- 
turnal catch. These field studies confirm that blue- 
fish activity patterns are influenced by light and dark 
cycles and that this pattern exists in diverse envi- 
ronments beyond the Hudson River estuary. 
Factors that may be responsible for changes in diel 
activity or movements of fishes include foraging 
(Sciarrotta and Nelson, 1977; Wurtsbaugh and Li, 
1985), reduction in predation risk (Clark and Levy, 
1988; see Hobson, 1991), spawning (Conover and 
Kynard, 1984), and thermoregulation (Caulton, 1978; 
Rountree and Able 1993; Neverman and Wurtsbaugh, 
1994). These factors may be interdependent. For ex- 
ample, Neverman and Wurtsbaugh ( 1994) found that 
Bear Lake (Utah-Idaho) YOY sculpin were able to 
digest their gut contents in a short period (overnight) 
by moving into warm surface waters at night. By 
digesting their food overnight, these fish were able 
to feed the following day. Clark and Levy (1988) 
showed that the vertical migration of juvenile sock- 
eye salmon in an Alaskan lake during the day could 
be explained as a tradeoff between foraging and pre- 
dation risk. For juvenile estuarine fishes, Miller and 
Dunn (1980) considered foraging as the primary 
cause of diel movements. 
If bluefish movements are directly related to for- 
aging, we might expect a strong correlation between 
the abundance of bluefish and their prey. Bluefish 
may congregate where prey density is high, or prey 
