Wuenschel et al : Habitat and diet overlap of 4 piscivorous fishes 
365 
(Sagarese et al., 2011). Predation on juvenile Weak- 
fish has also been observed in Delaware Bay by adult 
Weakfish and Summer Flounder (Taylor, 1987). 
A recent synopsis of diets documented across the 
continental shelf in the region indicated that Weakfish 
occurred at relatively low levels (~5%) in diets of Blue- 
fish, Summer Flounder, and Weakfish (Smith and Link, 
2010). Although direct predation on Weakfish by the 
4 piscivores investigated was high at different times 
during our study, large numbers of Weakfish were also 
collected in our surveys, indicating high availability of 
this prey type. However, the possibility that the high 
degree of predation may influence the continuing low- 
population levels of Weakfish (NEFSC 2 ) needs further 
study, especially because some of these predators, such 
as Summer Flounder (Able et al., 2011) and Striped 
Bass, have reached high population levels in recent 
years (ASMFC 3 ). 
Another prey species, Atlantic Menhaden, has re- 
ceived increased attention because of its historical im- 
portance as the main prey of Striped Bass at other lo- 
cations during other times (Nelson et al., 2003; Walter 
et al., 2003; Overton et al., 2008). Uphoff (2003) sug- 
gested that a shortage of Atlantic Menhaden as prey 
for Striped Bass in the Chesapeake Bay may have re- 
duced the nutritional condition of those Striped Bass in 
the 1990s, making them susceptible to disease. In our 
study, there was little evidence of Atlantic Menhaden 
in the diets of any of these predators except in October 
when Striped Bass, Weakfish, and Bluefish consumed 
them to some degree, although Atlantic Menhaden are 
typically present in the area during the other months 
(Ahrenholz, 1991; Smith, 1999). Adult Atlantic Menha- 
den occur along the coast in summer (Smith, 1999), but 
YOY Atlantic Menhaden reside in estuaries in summer 
and are not plentiful in the ocean until October (Able 
and Fahay, 2010), when they appeared in the diets of 
the piscivores examined in our study. Adult Atlantic 
Menhaden exceed the gape limitation for most of the 
species size classes examined, except that for Striped 
Bass and large Bluefish; therefore, it is not surprising 
that little consumption of this species was documented 
in summer. Diet analyses for larger predator species 
and larger individuals of those species considered in 
our study are needed to fully evaluate consumption of 
large Atlantic Menhaden in the Middle Atlantic Bight. 
As with our study, Woodland and Secor (2011) re- 
ported no clupeids in the diet of YOY Bluefish collected 
2 NEFSC (Northeast Fisheries Science Center). 2009. 48th 
Northeast Regional Stock Assessment Workshop (48th SAW) 
Assessment Report. U.S. Dept. Commer., Northeast Fish. 
Sci. Cent. Ref. Doc. 09-15, 834 p. [Available from National 
Marine Fisheries Service, 166 Water Street, Woods Hole, MA 
02543-1026 or http://www.nefsc.noaa.gov/nefsc/publications/.] 
3 ASMFC (Atlantic States Marine Fisheries Commission). 
2011. Striped Bass Stock Assessment Update 2011, 207 p. 
Prepared by the Striped Bass Stock Assessment Subcom- 
mittee and Striped Bass Tagging Subcommittee. [Available 
from http://www.asmfc.org/speciesDocuments/stripedBass/re- 
ports/stockassmts/20 HStripedBassAssmtUpdate.pdf] 
on the inner continental shelf off Maryland in August, 
although clupeids made up 9% of the diet of YOY Blue- 
fish collected in Chesapeake Bay in the same month. 
However, Atlantic Menhaden contributed a large por- 
tion to Bluefish diets, but less so for Summer Floun- 
der in Long Island bays (Sagarese et al., 2011), and 
large proportions to the diets of Weakfish, Bluefish, and 
Sandbar Shark ( Carcharhinus plumbeus) in Delaware 
Bay (Taylor, 1987), underscoring the importance of At- 
lantic Menhaden as prey in estuaries during summer. 
Additionally, we acknowledge that the degree of con- 
sumption and overlap in diets may vary with the popu- 
lation size of the predators. At the time of our study, 
the populations of Striped Bass (ASMFC 3 ) and Sum- 
mer Flounder (Able et al., 2011; Terceiro, 2011) were 
relatively high and the populations of Bluefish (Shep- 
herd and Nieland 4 ) and Weakfish (NEFSC 2 ) were rela- 
tively low. More detailed estimates of population-level 
consumption with more diet information from larger 
size classes would help to determine the direct effect 
of the predation of these piscivores on Weakfish and 
Atlantic Menhaden populations. 
One behavioral attribute that may reduce resource 
overlap between these predators is their use of the wa- 
ter column. Recent studies have indicated that a pre- 
sumed benthic species, Summer Flounder, may spend 
considerable time in the water column (Yergey, 2011; 
Henderson, 2012). This observation is consistent with 
the surprisingly large proportion of pelagic prey in 
their diets and their ability to feed in the water column 
in the laboratory (Olla et al., 1972). In addition, aggre- 
gation of diet data across the 24 h cycle may obscure 
some interactions with prey that undergo diel migra- 
tions (e.g., mysids and Summer Flounder; Buchheister 
and Latour, 2011). Although sampling was limited to 
daylight hours, given that gut evacuation rate gener- 
ally decreases with fish size (Wuenschel and Werner, 
2004) and with the relatively slow passage of food in 
carnivores (Smith, 1989; Adams and Breck, 1990), the 
results of our study capture much of the nighttime 
feeding habits of the predators examined. 
Another caveat to consider when evaluating overlap 
in habitat between these species is that overlap may 
be confounded by the length of a tow with a relatively 
large net. Although the duration of tows was short in 
our study, the distance covered (-1.85 km) may have 
included multiple discrete habitats, inflating assess- 
ments of overlap. However, the overlap estimates were 
not systematically high and the area covered per tow 
was very small relative to the overall study area and to 
the distances that the species examined are known to 
move; therefore, analysis at the tow level is appropriate. 
This study has described in fine spatial and tem- 
poral detail the degree of overlap in habitat and diet 
4 Shepherd, G. R., and J. Nieland. 2010. Bluefish 2010 stock 
assessment update. U.S. Dept. Commer., Northeast Fish. 
Sci. Cent. Ref. Doc. 10-15, 33 p. [Available from National 
Marine Fisheries Service, 166 Water Street, Woods Hole, MA 
02543-1026 or http://www.nefsc.noaa.gov/nefsc/publications/.! 
