246 
Fishery Bulletin 119(4) 
River where juvenile and adult Gulf sturgeon have previ- 
ously been captured (A. Kaeser, unpubl. data), as well as in 
other nearby reaches of the river (Fig. 1). 
Fish tagging 
From May through August of 2013-2018, we sampled for 
Gulf sturgeon 4-5 d/week. Each day, we deployed 6-12 
anchored monofilament gill nets throughout the river 
channel at depths of 4-18 m. All nets comprised three 
50-m panels consisting of 7.6-, 8.9-, and 10.2-cem monofil- 
ament mesh (stretch measure). Net design was based on 
nets proven to capture juvenile Atlantic sturgeon in rivers 
in Georgia (Schueller and Peterson, 2010). Nets were typ- 
ically soaked for 60-120 min, depending on conditions. To 
ensure that sampling occurred within the recommended 
water-quality ranges (Kahn and Mohead, 2010), we used a 
YSI Pro2030° meter (YSI Inc., Yellow Springs, OH) to mea- 
sure water temperature (in degrees Celsius), dissolved 
oxygen (in milligrams per liter), and salinity (using the 
practical salinity scale) at each netting location. River dis- 
charge data were obtained from the nearest U.S. Geological 
Survey stream gage (02359170 on the Apalachicola River 
near Sumatra, Florida; data available from website.). 
As nets were retrieved, all captured Gulf sturgeon were 
immediately removed and placed into a floating net pen 
where they could recover before being brought on board 
the vessel for data collection. Each individual was exam- 
ined for marks indicating previous capture; if no mark was 
present, the fish was marked with a passive integrated 
transponder (PIT) tag inserted into the musculature at the 
base of the dorsal fin or under the fourth dorsal scute. The 
fish was then weighed to the nearest gram, measured to 
the nearest millimeter (in fork length [FL]), and released 
at the site of capture within 30 min of initial capture. 
Fish ages were first assigned from modal distributions 
on length—frequency histograms of catch of Gulf sturgeon 
for each year of the study, by using the method described 
by Peterson et al. (2000) and Schueller and Peterson 
(2010). To validate assigned ages, we obtained sections 
of second marginal fin rays from the pectoral fins of a 
subsample of captured fish; these samples were prepared 
by using techniques described by Baremore and Rosati 
(2014). Ages were determined on the basis of consensus of 
3 independent readers (if consensus could not be reached, 
we removed that sample from the validation data set). 
Because there was essentially no overlap in lengths at 
age, we were able to assign a length range for age-1 and 
age-2 Gulf sturgeon. 
Acoustic telemetry 
To investigate the closure of the summer aggregation 
site in the Brothers River during the fishing period and 
to examine overwinter survival, we tagged up to 20 age-1 
8 Mention of trade names or commercial companies is for identi- 
fication purposes only and does not imply endorsement by the 
National Marine Fisheries Service, NOAA. 
juveniles (age estimated on the basis of length) with a 
surgically implanted acoustic transmitter (Vemco V7-4X, 
Innovasea Systems Inc., Boston, MA) in May and June 
of each study year. To implant the transmitter, we placed 
each fish in a V-shaped surgical platform, with a battery- 
powered pump supplying fresh river water to its gills. 
An incision of 2-3 cm was made along the midline of the 
abdomen by using a sterile scalpel, and through this inci- 
sion the sanitized transmitter (~1.6 g) was inserted into 
the body cavity. The incision was then closed with a 2/0 
absorbable monofilament suture (Monoswift L943, CP 
Medical, Norcross, GA) by using a single interrupted pat- 
tern (Boone et al., 2013; Baremore and Rosati, 2014). After 
the surgical procedure, each fish was placed in a floating 
pen. Once a fish had regained its orientation and ability 
to swim, it was released at its capture site. Ping rate and 
battery life of transmitters varied among the study years 
(Table 1). The transmitters deployed in 2017 had a 120-d 
delay before they began transmitting, extending the bat- 
tery life of those tags through the summer of 2018, allow- 
ing us to confirm fish survival and improve estimates of 
overwinter survival. 
To detect the tagged juveniles after their release, we 
deployed an array of acoustic receivers throughout the 
Brothers and Apalachicola Rivers, their distributaries, 
and the East Bay subunit of Apalachicola Bay (Fig. 1). 
The array consisted of 30 stationary acoustic receivers 
(Vemco VR2W, Innovasea Systems Inc.). Receivers were 
anchored to the bottom with concrete weights and held 
upright (hydrophone upward) in the water column with 
a PVC float. Receivers were attached to trees, naviga- 
tional markers, or other pilings by using stainless steel 
cables. Some were secured to pilings with aluminum 
U-channel, and others were deployed in open water, 
where they were anchored with cinder blocks. Every 2-3 
months throughout the study period, the entire receiver 
Table 1 
Specifications for acoustic transmitter tags implanted in 
age-1 juvenile Gulf sturgeon (Acipenser oxyrinchus deso- 
toi) captured and tagged from May through August in 
2013-2018 in the Brothers River and other areas of the 
Apalachicola River system in Florida. All tags were Vemco 
V7-4X transmitters with a frequency of 69 kHz. Minimum 
and maximum delays, and delay before activation, were 
set by the manufacturer. Transmitter lifespan was esti- 
mated by the manufacturer. 
Delay 
Max. delay before 
between Lifespan activation 
signals (s) (d) (d) 
Min. delay 
between 
signals (s) 
80 160 305 
170 310 426 
170 310 426 
80 160 374 
