Stehlik et al.: Distribution of 3 predatory fish at a salinity front in a small estuary 
151 
Figure 5 
Plots of home ranges derived from acoustic detections of ultrasonically tagged fish in the Navesink River in 
New Jersey: age-0 bluefish iPomatomus saltatrix) in (A) 2006 and (B) 2007 and age-l+ bluefish in (C) 2006 
and (D) 2007. Parallel dashed lines denote Reaches 1-4 of the estuary. 
The increased proportion of fish in the predator di¬ 
ets as the year progressed is attributable to 2 factors: 
1) increased availability of fish prey and 2) growth of 
predators that allowed them to catch larger prey. The 
proportion of fish in relation to invertebrates in the di¬ 
ets of young bluefish, weakfish, and striped bass simi¬ 
larly has been reported to increase in other estuaries 
during the summer (Hartman and Brandt, 1995; Wood¬ 
land et al., 2011) as forage fish grow to available size. 
In mid-Atlantic estuaries, the fluctuating availabil¬ 
ity of Atlantic menhaden has had a key effect on diets 
of predatory fish. In the Chesapeake Bay, Atlantic men¬ 
haden dominated the diets of striped bass in the 1950s 
(Griffin and Margraf, 2003). They also contributed 
more than 60% by weight to the diet of age-2-i- bluefish, 
striped bass, and weakfish in 1990 and 1992 (Hartman 
and Brandt, 1995). Although Atlantic menhaden were 
important in the diets of bluefish and weakfish in the 
Navesink River in 1998, 1999, and 2007, they were ab¬ 
sent from the stomachs of age-0 bluefish collected in 
nearby Sandy Hook Bay in the 1980s (Friedland et al., 
1988). The low abundance of Atlantic menhaden in the 
mid-Atlantic region in the 1990s and 2000s (Ferry and 
Mather, 2012; Pikitch et al., 2012) led to their decrease 
in the diets of striped bass in Chesapeake Bay and was 
suspected to be linked to poor physical condition of the 
striped bass themselves (Uphoff, 2003; Walter et al., 
2003; Jacobs et al., 2009). 
Home ranges and habitat associations of predators 
Our study is the first to map the home ranges of 3 pred¬ 
ators at the same location and time, to examine stom¬ 
ach contents, and to collect potential prey. The results 
of this study were consistent between 2006 and 2007, 
both in location and in dimension of home ranges. We 
found that home ranges were fairly small and similar 
in size among the 3 predators, indicating that the ani¬ 
mals lock into small core areas or hotspots. The centers 
of home ranges were often situated in one of the deeper 
channels or basins directly downriver from the salin¬ 
ity front, particularly for weakfish. Age-0 bluefish was 
the only fish cohort that was detected consistently on 
both sides of the salinity front, in reach 4. Age-l-i- blue¬ 
fish had larger home ranges than age-0 bluefish, pos¬ 
sibly because their greater body size allowed greater 
swimming speed (Beamish, 1978; Stehlik, 2009). Home 
ranges overlapped spatially, yet the occupation of those 
spaces was separated temporally. The overlap in the 
diets of predators parallels the overlap of their home 
ranges. The dimensions of the home ranges of these 3 
predators have been found to be similar in other small 
