May et al.: Fine-scale movements of Pristis pectinata 
361 
Most of the occupied nurseries of the smalltooth sawfish 
(Pristis pectinata), listed as endangered under the U.S. 
Endangered Species Act (Federal Register, 2003), are in 
southwest Florida. Charlotte Harbor, located on the Gulf 
of Mexico, has been identified as 1 of 2 units that com¬ 
pose the critical habitat for promoting recovery of juve¬ 
niles (Norton et al., 2012). The Charlotte Harbor estuarine 
system contains 2 distinct nurseries: 1 nursery associated 
with the Peace River (-10 km long) in the northern por¬ 
tion of the system, and 1 nursery in the Caloosahatchee 
River in the southern portion (-25 km long) (Scharer 
et al., 2017). In the Caloosahatchee River nursery, there 
are multiple hotspots, whereas in the Peace River there 
is only one (Poulakis et al., 2011). These nursery hotspots 
are important because adult females give birth nearby 
biennially and the young stay for 1-2 years; as a result, 
these areas contain multiple year classes and are prior¬ 
itized for conservation, especially when the entire nurs¬ 
ery cannot be preserved (Poulakis et al., 2016; Feldheim 
et al., 2017). Because criteria to establish broad nurser¬ 
ies and hotspots within nurseries are complementary 
(Poulakis and Grubbs, 2019), data from nursery hotspots 
have already influenced key decisions regarding manage¬ 
ment in southwest Florida (NMFS 1 ). 
The single hotspot in the Peace River was identified by 
using public encounter, scientific catch, and acoustic data 
and was initially thought to be confined to the northern 
shoreline (Poulakis et al., 2011). However, the boundar¬ 
ies of this hotspot were expanded after active tracking 
revealed nightly excursions toward the southern shore¬ 
line of the river (Huston et al., 2017). Interestingly, small¬ 
tooth sawfish have remained associated with this nursery 
hotspot regardless of seasonal changes in abiotic condi¬ 
tions (Scharer et al., 2017). 
In August 2015, the Nature Conservancy began a pilot 
oyster restoration project along the southern shoreline 
of the Peace River, given the importance of oysters to 
overall estuarine health (Beck et al., 2011). Oysters 
contribute to the health of estuaries by providing water 
filtration, 3-dimensional habitats, and storm buffering 
(Coen et al., 2007; Rodriguez et al., 2014). Because the 
restoration area was within designated critical habitat 
of juvenile smalltooth sawfish, it became important to 
determine how juveniles were using this area and to 
document any interactions they had with the develop¬ 
ing reefs. 
To document habitat use by smalltooth sawfish in and 
around the southern shoreline of the Peace River, time- 
synchronized acoustic receivers were added to a preexist¬ 
ing receiver array to obtain estimates of the position of 
sawfish accurate to within 5 m. The specific goals of this 
study were 1) to determine if juveniles were regularly 
using the southern shoreline of the river, 2) to determine if 
the timing of river crossing to the southern shoreline was 
related to the tidal cycle, and 3) to identify any patterns 
of habitat use and movement along the southern shoreline 
1 NMFS. 2019. Unpubl. data. Southeast Reg. Off., Natl. Mar. Fish. 
Serv., NOAA. 263 13th Ave. S., St. Petersburg, FL 33701. 
by different age classes (YOY and >age 1). These data will 
improve our understanding of how hotspots function as 
the most productive habitats within smalltooth sawfish 
nurseries. 
Materials and methods 
Study area 
Charlotte Harbor is one of the largest estuaries in Flor¬ 
ida with an area of about 700 km 2 (Hammett, 1990). 
The main study area was along the southern shore¬ 
line of the Peace River, where an oyster restoration site 
was located (Fig. 1). Prior to this study, 3 oyster reefs 
were constructed by the Nature Conservancy 16 m from 
shore. The shoreline was dominated by red mangroves 
(Rhizophora mangle ), and the water depth ranged from 
0.1 m along the central and easternmost portions of the 
main study area to 1.2 m along the westernmost portion. 
The tidal regime is mixed semidiurnal, generally result¬ 
ing in 2 high and 2 low tides of variable heights each day 
(Zheng and Weisberg, 2004). 
Field sampling 
Gill-net sampling for smalltooth sawfish was conducted 
from February through September 2016 as part of an 
ongoing research program (Poulakis et al., 2011). Each 
month, 2 random sampling trips (4 sites per trip) and 
an average of 2 directed sampling trips (3 sites per 
trip) were made in upper Charlotte Harbor, including 
in the Peace River (for details, see Scharer et al., 2017). 
Directed sampling sites were selected on the basis of his¬ 
toric capture locations or recent encounters reported by 
the public. All nets were soaked for 1 h and checked after 
0.5 h or when animals were observed in the net, which¬ 
ever came first. Sawfish were measured to the nearest 
millimeter in stretch total length (STL) and tagged prior 
to release. 
Acoustic transmitters 
All captured smalltooth sawfish were externally tagged with 
69-kHz Vemco 2 (Bedford, Canada) V9 acoustic transmitters 
(hereafter referred to as tags', tag family: V9-2H; code space 
ID: A69-1303; length: 29 mm; weight in water: 2.9 g). Tags 
were programmed to emit a unique acoustic sequence every 
80-160 s. Delays were used to reduce signal collisions when 
multiple individuals were within range of the same acous¬ 
tic receivers and to maximize battery life (—12 months). 
The 69-kHz tags also functioned with the existing acoustic 
receivers deployed broadly throughout the estuary (see the 
“Acoustic monitoring” section). 
2 Mention of trade names or commercial companies is for iden¬ 
tification purposes only and does not imply endorsement by 
the Florida Fish and Wildlife Conservation Commission or the 
National Marine Fisheries Service, NOAA. 
