May et al.: Fine-scale movements of Pristis pectinata 
365 
Flood tide occurrence Ebb tide occurrence 
Figure 2 
Activity of tagged smalltooth sawfish (Pristis pectinata) 
relative to the mixed semidiurnal tidal regime of the study 
area in the Peace River, Florida, from May through October 
2016. Box plots from Kruskal-Wallis tests compare the 
median number of detections per hour of 6 sawfish within 
an array of acoustic receivers between the first and sec¬ 
ond flood tides each day and between the first and second 
ebb tides each day. The bottom and top boundaries of the 
box represent the 25th and 75th percentiles, respectively, 
of the number of detections per hour. The line within the 
box is the median value. Whiskers above the boxes indicate 
the 90th percentiles. Black circles indicate outlying values 
for upper ranges. Significantly more position estimates 
were placed on the southern shoreline during the first 
flood and first ebb tides (regardless of height), which typi¬ 
cally occurred at night. Because these first tides typically 
occurred at night, the primary driver for the across-river 
movement was likely diel, rather than tidal. 
oyster habitats. The wide Cl for oyster habitats reflects 
greater variability in associations of sawfish with this 
habitat. 
Although there were differences in habitat use among 
individuals, both size classes used all available habitats, 
and 5 of 6 individuals crossed over the oyster habitats 
(Table 2; Fig. 3). Furthermore, because most juveniles 
crossed the constructed oyster reefs, they were not actively 
avoiding the developing reefs. 
Use of the southern shoreline varied ontogenetically, 
with detections of age-1 or older individuals peaking 
in June. Although a small number of detections of YOY 
occurred in June and July, detections in the VPS of YOY 
peaked in August and September. 
Hotspot-wide movement patterns 
In general, smalltooth sawfish made diel movements in 
the Peace River (Fig. 4). During the day, sawfish were con¬ 
centrated near the protected cove portion of the northern 
shoreline as well as farther downriver along the northern 
shoreline. At night, they were still concentrated in these 
2 areas but were more numerous downriver. 
Table 2 
Comparison of results from likelihood ratio chi-square 
tests (G 2 ) and selection ratio tests (iDy) for the 6 small¬ 
tooth sawfish (Pristis pectinata ) detected frequently from 
May through October 2016 near the constructed oyster 
reefs along the southern shoreline of the Peace River, 
Florida. Sawfish were tagged with acoustic transmitters 
and tracked with an array of acoustic receivers in 3 hab¬ 
itat types: shallow (<1 m), deep (>1 m), and oyster reef. 
Selection ratios >1 indicate selection for a habitat type; 
ratios <1 indicate selection against a habitat type. Saw¬ 
fish ID numbers correspond to those in Table 1. For habitat 
descriptions, see the “Materials and methods” section. 
number 
G 2 
df 
P 
Shallow 
Deep 
Oyster 
3 
1983.25 
2 
<0.01 
4.84 
0.76 
5.56 
15 
1030.70 
2 
<0.01 
4.03 
0.81 
3.39 
16 
30.50 
2 
<0.01 
1.82 
0.89 
2.32 
17 
38.50 
2 
<0.01 
1.53 
0.98 
0.00 
18 
447.83 
2 
<0.01 
7.75 
0.57 
5.81 
19 
507.82 
2 
<0.01 
4.22 
0.80 
4.62 
Although some individuals moved only along the north¬ 
ern shoreline, smalltooth sawfish used both shorelines 
(Fig. 5). The majority (91%) of detections at the VPS 
occurred at night, and over half (63%) of the daytime 
detections were of the largest individual. Sample size was 
low, but this finding suggests that there are ontogenetic 
differences in hotspot-wide habitat use: larger juveniles 
(>1500 mm STL) were more likely to make farther excur¬ 
sions during the day. 
Diel movements were evident within the entire nursery 
hotspot over short time scales (e.g., 1 week; Fig. 6) and 
over the course of the entire study (Fig. 7). Individuals 
generally remained along the northern shoreline during 
the day and made nightly excursions toward the middle of 
the river, sometimes to the southern shoreline, and back. 
Discussion 
Currently, for the smalltooth sawfish in the United 
States, habitat use by juveniles is monitored and related 
management actions can be implemented on 3 spatial 
scales (see inset in Fig. 1). First, nursery hotspots are rel¬ 
atively discrete areas within the broader nursery where 
YOY and juveniles age 1 or older commonly occur over 
many years (i.e., the most productive nursery habitats; 
Nagelkerken et al., 2015). Young may be born elsewhere 
in the broader nursery, but they tend to go to nursery 
hotspots and spend most of their time there, even when 
disturbances, such as tropical storms or cold fronts, tem¬ 
porarily disrupt normal patterns of habitat use (Poulakis 
et al., 2016; Scharer et al., 2017). Therefore, nursery 
hotspots often contain at least 2 year classes and become 
