2012 COURSE DATES: AUGUST 4 – 17, 2012 - Sirenian International

Aerial surveys of manatees (Trichechus manatus) in Lee County, Florida 577
Fig. 2 Map illustrating locations of seagrass beds throughout the entire
study area (source: South Florida Water Management District 2003)
(Fig. 5a, b). This movement coincides with a significant
increase in mean number of manatees sighted per survey
(p=0.00102). From pre-winter to winter, manatees
became even more densely clustered (Fig. 5c), but the
increase in the mean number of manatees per survey was
not significantly different (p=0.582). During post-winter
there were generally fewer high-density areas and fewer
manatees sighted than there were for winter, indicating a
dispersal of manatees as the weather warmed (Fig. 5d).
Management
With regard to our study, the LCMLETF provided a stable
infrastructure for quick dissemination of individual flight
results to enhance conservation efforts with the near real-time
information gathered. The information we provided regarding
distribution, density, and behavior of manatees was reported to
resource managers and LCMLETF coordinators, and was
subsequently used to position marine enforcement units in the
most critical areas to provide additional protection in needed
areas.
A comparison between the Kernel density analyses
(Figs. 4 and 5) and the county’s site-specific boat speed
zones (Fig. 3) show that, with a few exceptions, areas with
high densities of manatees year-round overlap well with
year-round speed zones, and areas with high densities
during “non-winter” months overlap remarkably well with
the seasonally (Apr 1–Nov 15) designated zones. There
appear to be relatively few areas where high densities of
manatees are found year-round in seasonally designated
zones and vice versa. While it would be in the interest of
local and state officials to identify these areas where
enforcement zones could be added or re-assessed, it is not
within the scope of this paper to do so.
Discussion
Aerial survey counts
The results reaffirm that Lee County supports large
numbers of manatees, particularly during fall and winter
months, and further emphasize the need for careful
management of this particular population. These results
can be compared to results from statewide synoptic surveys
which also indicate that a large proportion of the state’s
manatees is found in Lee County during winter. In the
January 2010 synoptic survey, biologists counted 5,067
manatees statewide, with 877 (approximately 17%) in Lee
County (H. Edwards FWC pers. comm.). This count was
approximately 200 manatees more than the highest count in
this study; however synoptic surveys are flown on days
where sighting conditions are optimal. In February of the
same year, after a prolonged period of cold weather, 905
manatees were counted at the Orange River FPL plant alone
(Reynolds, unpub. data).
Our surveys produced much higher counts of manatees
than did previous studies conducted in the area. The most
recent study prior to ours was completed by FWC from
1994 to 1998. For reference, the previous study reported an
average of 147.6 manatees counted per survey (Fish and
Wildlife Commission unpublished), whereas the mean
count in our study was 345 manatees per survey. However,
due to differences in flight path and overall survey effort,
comparison between the 1994–1998 counts and ours is not
straightforward. Regardless, both studies showed that
manatees were present in Lee County in much higher
numbers during winter than non-winter months. Also, the
highest counts from both studies were recorded on surveys
where large aggregations of manatees were present at
warm-water sites, indicating that animals traveled to Lee
County specifically for this resource and/or that manatees
aggregated at the plant are easier to count than smaller
groups of widely dispersed manatees. Survey data from the
Central region also showed that there were more manatees
present during winter than non-winter. However, over