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

Aerial surveys of manatees (Trichechus manatus) in Lee County, Florida 579
Table 1 Total number of manatees observed on each of 34 flights,
and total number of manatees observed in the Central region
Survey date Survey total Central region total
4/2/2007 158 24
4/24/2007 179 44
5/17/2007 216 70
5/29/2007 235 52
6/8/2007 203 18
6/28/2007 207 56
7/2/2007 216 78
7/9/2007 220 96
8/13/2007 242 90
8/20/2007 135 37
9/7/2007 234 84
10/8/2007 203 90
11/6/2007 398 180
11/20/2007 499 211
12/3/2007 504 233
12/18/2007 396 163
1/7/2008 416 89
2/19/2008 465 193
4/17/2008 353 117
5/13/2008 414 104
5/27/2008 349 105
6/6/2008 357 125
7/18/2008 244 106
8/28/2008 288 96
10/8/2008 357 187
11/5/2008 497 294
12/8/2008 420 151
12/18/2008 485 283
1/9/2009 518 188
2/27/2009 626 328
3/9/2009 610 211
3/30/2009 411 127
4/10/2009 261 91
4/29/2009 397 113
Total 11713 4434
Table 2 Lee County survey study area: total number of surveys,
manatees sighted, and the mean number of manatees sighted ± one
standard error per survey for each specified time period
Winter Non-winter
# of Surveys 11 25
Total # Manatees 4939 6774
Mean #/Survey 494±24 282±20
Table 3 Central Region: total number of surveys, manatees sighted ± one
standard error, and the mean number of manatees sighted per survey for
each specified time period
Pre-winter Winter Post-winter Summer
# of Surveys 4 10 6 14
Total # of Manatees 751 2050 516 2384
Mean #/Survey 188±42 205±21 86±17 80±8
need to operate as efficiently as possible. Therefore, the
identification of important seasonal habitats where management
and enforcement efforts should be focused is an
essential outcome of this study.
Spatial data for the Central region also show an
interesting post-winter pattern. At this time, manatees focus
on feeding, but their distributions are more similar to
summer patterns, which are more widely distributed. When
cold weather ceases, manatees appear to disperse quickly,
returning to forage in areas other than those within San
Carlos Bay and Matlacha Pass. This rapid dispersal pattern
has previously been noted as a contributing factor to the
mass mortality of manatees and other marine animals in
southwest Florida during a 1996 red-tide event (Landsberg
and Steidinger 1998). This paper concluded that manatees are
at high risk from February through April should a “perfect
storm” of environmental factors combine to generate persistent
red-tide blooms in the region. Exposure to the neurotoxins
produced by the bloom-forming dinoflagellate, Karenia
brevis, causes disorientation and severe health problems in
manatees (O’Shea et al. 1991; Bossart et al. 1998), making
them particularly vulnerable to boat strikes. While little can
apparently be done to prevent manatees from encountering
these blooms, increased protection against human-related
threats during such events should be a priority for managers.
Manatee travel patterns within seasons are also of concern
to resource managers. For example, surveyors observed that
on the coldest winter days most manatees were found at
warm-water sites, whereas on warmer days between cold
fronts many of them were found in San Carlos Bay,
presumably foraging. In order to make this transition from
one critical resource to another, manatees must travel a
minimum of 38 km up or down the Caloosahatchee River.
This is a concern for managers since the primary travel
corridor for manatees coincides with the primary channel for
boat traffic. Even more troublesome, a 1998 study assessing
the effectiveness of speed zones at multiple sites within this
river yielded an overall compliance of just 58% (Gorzelany
2004). Although this study considered only a subset of Lee
County waters, without evidence to the contrary it can be
assumed that compliance throughout the rest of the county is
similar to that of the Caloosahatchee. On a more positive
note, Gorzelany (2004) also reported a significant increase in