Manderson et al.: Residence time and habitat duration for predators in a small mid-Atlantic estuary 
147 
Table 1 
Median (Md) total lengths (TL) in millimeters, number of fish released, release dates, median number of detections, and 
median residence times (in days) of fishes released in 2006 and 2007with ultrasonic transmitters in the Navesink River, New 
Jersey, for a study of residence times and habitat duration of 3 predators: age-l+ Striped Bass (Morone saxatilis), age-0 and 
age-l+ Bluefish ( Pomatomus saltatrix), and age-l+ Weakfish ( Cynoscion regalis). Median days detected (i.e., residence time 
in days) and confidence limits (CL) were calculated with right-censored Kaplan-Meier survival analysis (see Fig. 3). Signifi- 
cant Spearman’s rank correlation coefficients (p) between release day and body length are shown in bold type. An asterisk 
(*) denotes that fishes caught by anglers before egress or detected by receivers on the last fall day of the experiment were 
censored (Striped Bass=l, age-0 Bluefish=4, age-l-i- Bluefish=l, and Weakfish=l). 
Species-and- 
age class 
Year 
Md TL 
(Range) 
Number 
released 
Release 
dates 
Release date 
vs. length 
Spearman’s p, 
P-value 
Md number 
of detections 
(range) 
Md days 
(95%CL) 
(range) 
Striped Bass 
2006 
465 
34 
15May-28Jun 
0.41, 0.016 
2475 
16(9,28) 
(359-630) 
(343-20331) 
(2-58*) 
2007 
442 
12 
3May-19Jun 
0.76, 0.004 
1469 
8(7, °°) (2-50) 
(342-510) 
(22-3440) 
Age-l-i- Bluefish 
2006 
335 
14 
5Jun-16Aug 
0.45, 0.107 
5428 
19(16,42) 
(310-390) 
(311-17586) 
(10-48) 
2007 
455 
21 
lMay-19Jun 
-0.83, <0.001 
3543 
29(20,46) 
(310-610) 
(60-21174) 
(3-88) 
Age-0 Bluefish 
2006 
210 
15 
27Aug-9Sep 
0.68, 0.005 
2503 
29(21,oo) 
(175-270) 
(291-7889) 
(5-37*) 
2007 
246 
30 
29Aug-21Sep 
0.28, 0.140 
1706 
29(22,37) 
(222-275) 
(101-6777) 
(1-52*) 
Weakfish 
2006 
337 
15 
13Jul-16Aug 
0.32, 0.244 
4040 
33(22, oo) 
(224-535) 
(41-16568) 
(4-64*) 
2007 
389 
26 
29Jun-90ct 
-0.42, 0.034 
1708 
47(35,70) 
(304-500) 
(31-11391) 
(6-88*) 
con, Somerville, NJ). We measured the total length (TL) 
of each fish in millimeters and inserted unique anchor 
tags into the dorsal muscle. Fishes recovered from an- 
aesthesia in <9 min and were monitored for 2-48 hours 
in flow-through laboratory tanks. We released fishes in 
good condition at randomly selected locations in the 
river. This random release approach was used to moni- 
tor initial patterns of habitat selection during the first 
24-48 hours. We released <5 individuals of each age 
class for each species per week to observe movements 
over the broadest range of environmental conditions. 
Striped Bass, Weakfish, and age-l+ Bluefish (n>12 
for all classes) implanted with replica transmitters 
survived >120 d in the laboratory (B. Phelan and J. 
Rosendale, unpubl. data). Several age-0 Bluefish <170 
mm TL died after implantation of replica transmitters. 
We, therefore, released only Bluefish >175 mm TL with 
active transmitters in the field. 
Analyses 
In this investigation, we analyzed predator residence 
times in and egress from the estuarine tributary rather 
than movements within the tributary. We eliminated 
data from 2 tagged fishes whose movement trajectories 
indicated that they died shortly after release. Then, we 
aggregated data collected at all receivers to calculate 
the presence or absence of each fish in the estuary for 
each day of observation. Individuals detected in the 
lower estuary and subsequently not detected for 24 h 
were considered absent. Several fishes detected at the 
upstream receiver in the Swimming River disappeared 
for a short time and then were detected in the Swim- 
ming River or upper Navesink River. We assumed these 
fishes had spent that time upstream of the receiver ar- 
ray and, therefore, had remained in the estuary. We 
performed all analyses with R software (R Core Team, 
2013). 
We estimated the number of days that tagged fishes 
used the estuary with right-censored Kaplan-Meier 
survival analysis (Bennetts et al., 2001). We censored 
5 age-0 Bluefish and 1 Striped Bass detected in the 
estuary when receivers were removed in the fall, and 
1 Weakfish caught by an angler in the Navesink River. 
In survival analysis, observations are censored when 
the study ends before the event response occurs (in this 
case, egress) or when an individual is removed from 
the study (e.g., dies) before the event response occurs. 
