Manderson et al.: Residence time and habitat duration for predators in a small mid-Atlantic estuary 
145 
and age-l+ Pomatomus saltatrix) and Weakfish (age- 
1+ Cynoscion regalis ) — to habitat conditions in a small 
mid-Atlantic estuarine tributary that serves as a sum- 
mer feeding and nursery ground. Individuals of these 
3 species undertake broad-scale seasonal migrations of 
100s to 1000s of kilometers along the Atlantic coast of 
the United States but can exhibit site fidelity in sum- 
mer feeding and nursery habitats (Ng et al., 2007; Tay- 
lor et al., 2007; Pautzke et al., 2010; Turnure, 2010). 
They occupy upper trophic levels in mid-Atlantic es- 
tuarine food webs and are responsible for the transfer 
of nutrients and energy between benthic and pelagic 
compartments within estuaries and between estuaries 
and the coastal ocean (Hagy, 2002; Krause et al., 2003; 
Johnson et al., 2009). 
We report on the seasonal and size-dependent pat- 
terns of residency of these predators in a small tribu- 
tary (surface area of -1000 ha) in New Jersey over 2 
years. We use generalized additive mixed models to 
quantify size-dependent relationships of time of estu- 
arine residence to water temperature and freshwater 
discharge. We assume that residency and flux rates 
of individuals through the estuary reflect the timings 
and durations when habitat resources support survival, 
metabolic maintenance, and at least adequate growth, 
except when emigration is triggered by changes in re- 
quirements associated with life-history-event schedules 
(e.g., timing of spawning) (Charnov, 1976; Winkler et 
al., 1995; Belisle, 2005). 
Materials and methods 
Study area 
We performed acoustic biotelemetry in the Navesink 
River, New Jersey, a tributary of the Hudson-Raritan 
Estuary (Fig. 1), described in detail in other stud- 
ies (Shaheen et al., 2001; Stoner et al., 2001; Scharf 
et al., 2004; Manderson et al., 2006). The Navesink 
River is nearly 1.5 km wide and extends -12 km 
east from its primary freshwater source, the Swim- 
ming River, to the Shrewsbury River and then to the 
Hudson-Raritan Estuary where it connects to the At- 
lantic Ocean. Salinities range from as low as 0.08%c 
at the head of the Swimming River to -27 %c at the 
confluence of the Navesink and Shrewsbury rivers. 
The tidal range averages 1.4 m. Tidal currents are 
flood dominated and attenuate in the middle and up- 
per river, an area that is both deeper (mean depth 
[p D] = 1.5 m mean low water [MLW]; maximum of ~9 
m) and has sediments of finer grains than the lower 
river (p D=1.0 m MLW; maximum of ~6 m) (Chant 
and Stoner, 2001; Fugate and Chant, 2005). The low- 
er river has a complex network of channels flanked 
by sandbars and vegetated coves. 
Infrastructure of the estuarine observatory 
Fishes tagged with ultrasonic transmitters were de- 
tected with an array of omnidirectional receivers (mod- 
el VR2, VEMCO 1 * , Bedford, Canada) moored throughout 
the Navesink River from May 15 to October 3, 2006, 
and from April 18 to October 31, 2007 (Fig. 1). We at- 
tached receivers to anchored lines that had surface and 
subsurface floats. The subsurface floats suspended the 
receivers -80 cm above the bottom. In 2006, the array 
consisted of 27 receivers. In 2007, we moored 5 addition- 
al receivers in several marsh creeks and coves. Nearest 
neighbor distances between receivers in the river aver- 
aged 493 m (standard deviation 141 m, within a range 
of 216-788 m). On the basis of range tests, receivers 
moored in the middle and upper river had detection 
ranges of 350-600 m. Detection ranges were smaller 
and more variable in the lower river, which is topo- 
graphically complex. The estuarine volume monitored 
by the array of all moored receivers was ~1.397xl0 7 m 3 
(surface area=932 ha) at MLW. In 2006, the receivers 
were retrieved in September. We subsequently discov- 
ered that a few tagged fishes remained in the estuary 
after the receivers were retrieved. Therefore, in 2007, 
receivers were left in place for an additional month. 
We measured environmental variation with moored 
instruments and supplemental mobile surveys. The 
moored instruments provided measurements -12 cm 
above the bottom of the seafloor at 20-min intervals 
and included 3 Star-Oddi (Gardabaer, Iceland) tem- 
perature, salinity, and pressure sensors; 3 YSI, Inc. 
(Yellow Springs, Ohio) temperature, salinity, pressure, 
and dissolved oxygen sensors; and an Aanderaa RCM 
9 (Aanderaa Data Instruments, Bergen, Norway) meter 
that measured current speed and direction, tempera- 
ture, salinity, pressure, and optical backscatter. Star- 
Oddi sensors were used throughout the system (Fig. 
1). YSI sensors were deployed in the upper river where 
episodes of low dissolved oxygen occur. We moored the 
RCM 9 in the channel that connects the lower and 
middle rivers. Weekly hydrographic surveys were per- 
formed from a 6-m vessel through the use of a Hydro- 
lab DataSonde probe (Hach Hydromet, Loveland, CO) 
with temperature and salinity sensors mounted 0.5 m 
below the surface of the water and integrated with a 
GPS, and a Sea-Bird Electronics, Inc. (Bellevue, WA) 
SBE 25 Sealogger CTD with temperature, conductivity, 
pressure, dissolved oxygen, photosynthetically active 
radiation, turbidity, and fluorometer sensors. During 
each weekly survey, we performed cross-sectional tran- 
sects of the river that intercepted all receiver moor- 
ings. The Hydrolab DataSonde and GPS continuously 
recorded temperate, salinity, and geographic position 
at 1-s intervals. Vertical profiles of the water column 
at each mooring were measured with the conductiv- 
1 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
