Manatee Movements in the Northern Gulf of Mexico and the Potential for Exposure to the Deepwater Horizon Oil Spill
Daniel H. Slone1, James P. Reid1, Allen Aven2 and Ruth H. Carmichael2
1U.S. Geological Survey Southeast Ecological Science Center 7920 N.W. 71st Street Gainesville, FL 32653
2Dauphin Island Sea Lab 101 Bienville Blvd. Dauphin Island, AL 36528
U.S. Department of the Interior U.S. Geological Survey
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MANATEES IN THE NGOM
1 Introduction
2 The West Indian Manatee (Trichechus manatus) is found throughout the coastal waters of the Gulf of
3 Mexico, with the Antillean subspecies (Trichechus manatus manatus) found in Mexico, and the
4 Florida subspecies (Trichechus manatus latirostris) found from Texas through to Florida (Deutsch et
5 al. 2008, Gunter, 1941; Fig. 1). Florida manatees have in recent years been documented in increasing
6 numbers in the northern Gulf of Mexico (NGOM), including Mobile Bay, the Wakulla River, and
7 other water bodies (Fertl et al. 2005, Pabody et al. 2009, Butler et al. 2011). Their habitat and
8 resource use in these areas have not been well documented, but as with other areas, they must access
9 seagrasses or other vegetation for forage, fresh water for drinking, and warm water in the winter for
10 refuge. Recently, oil from the Deepwater Horizon spill has impacted a large area of the NGOM,
11 including seagrass beds and nearshore areas that manatees are likely to use.
12
13 Since 2007, researchers from the USGS Southeast Ecological Science Center have been conducting
14 pilot studies on manatee movements and habitat use in the NGOM to document extent of migrations
15 and determine patterns of habitat use. We have been radiotagging and tracking wild manatees
16 throughout Florida since the late 1970’s (e.g. Deutsch et al. 2003, Reid et al. 1995), but this was the
17 first effort directed at understanding movement patterns of manatees in the NGOM, prompted by
18 increasing winter use in the Wakulla Springs watershed. Similarly, in 2009 researchers with Dauphin
19 Island Sea Lab (DISL) with Sea to Shore Alliance started tracking studies by tagging two manatees in
20 Mobile Bay to determine summertime habitat use in that estuary and migration routes to Florida
21 (Table 1).
22
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MANATEES IN THE NGOM
23 On April 20, 2010, the Deepwater Horizon oil drilling platform exploded, and over the next 86 days
24 the breached well released 4.9 million barrels of oil into the NGOM (NOAA 2010a). Reaction to the
25 spill from the marine mammal community was swift, with monitoring and rescue activity for several
26 species commencing before the flow of oil had stopped (MMC 2011). Researchers from the USGS
27 and DISL continued to track manatees in the NGOM during the time of the spill, and tagged
28 additional individuals
29
30 The tracking data from tagged manatees provided a foundation for us to analyze the movements of
31 manatees relative to the measured distribution of oil from the Deepwater Horizon as it related to travel
32 routes, seagrass beds, and other manatee habitats. The primary objective of this report is to compile
33 and evaluate those data for insights on possible impacts of the Deepwater Horizon spill on manatees
34 and their habitat in the NGOM. The study area includes nearshore areas that manatees may traverse or
35 utilize from Mobile Bay, AL to Crystal River, FL (Fig. 2)
36 Methods
37 For this study, we identified the following tasks:
38 1) Assemble existing background GIS datasets relating to manatee habitat in the NGOM and
39 spatial data on shoreline oiling from the Deepwater Horizon spill.
40 2) Compile available telemetry data from manatees tracked in the NGOM.
41 3) Analyze manatee movements, identify use of resources, and determine areas of potential
42 manatee interactions with oil, either directly on travel corridors, or indirectly, on seagrass
43 beds.
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44 GIS data
45 Pursuant to task 1, the following datasets were compiled:
46 1) Background images and polygon layers were obtained from NOAA and ESRI to depict the
47 shoreline and nearshore waters of the NGOM (Table 2).
48 2) From the USGS National Wetlands Research Center, We obtained polygon layers of seagrass
49 beds found in Alabama and Florida. These areas were of interest because by feeding on
50 seagrasses, manatees would be exposed to any toxins that were adhered to the grass, and
51 because they would tend to linger in those areas, they would also be exposed to toxins in the
52 water column.
53 3) From the Environmental Response Management Application website (ERMA,
54 http://gomex.erma.noaa.gov/erma.html), we downloaded the latest spatial data from Shoreline
55 Cleanup and Assessment Technique (SCAT) surveys that were performed along the Gulf
56 coast (NOAA 2010b; Table 2). The SCAT surveys provide a standardized measure of
57 shoreline oiling conditions for comparisons among locations. These datasets were used as a
58 proxy to indicate nearshore waters and habitats that may have been affected by oil.
59 Manatee Tagging
60 A USGS study was initiated in 2007 to identify manatee use patterns and habitats in the NGOM by
61 tagging and tracking manatees known to use the region. In September 2007, USGS researchers
62 attached a tracking tag to the tail of a manatee that had been rescued from a Citgo petroleum refinery
63 near Corpus Christi, Texas the previous winter. It was hoped that the manatee, named “Texas”, would
64 travel north in the Gulf of Mexico from its release location in Crystal River, FL, however Texas did
65 not venture much further north than Cedar Key, FL, while he was tagged. . In the spring and summer
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66 of 2008, three manatees were tagged in the Wakulla River. FL. Three manatees identified from photo
67 records as regular inhabitants of the northern Gulf were tagged in Crystal River the following winter.
68 During the summer of 2009, researchers at DISL began their tracking program by tagging two
69 manatees in Mobile Bay. A total of eight manatees were being tracked in the NGOM when the
70 Deepwater Horizon spill occurred, and an additional five were tagged and tracked in the following
71 months. Combined with the three manatees that were tracked prior to the oil spill, there were data
72 from a total of 17 manatees to analyze (Table 1).
73
74 The tracking devices used by both USGS and DISL were satellite-linked Global Positioning System
75 (GPS) tags (Telonics TMT-460 and TMT-462; http://www.telonics.com/) that were coupled with
76 System Argos (https://www.argos-system.org/) satellite transmitters. These were encased in floating
77 housings that were attached to a belt around their caudal peduncle of manatees via a 2 m long tether
78 (Deutsch et al. 1998) (Fig. 3). Both belt and tether were engineered with specific tensile strengths that
79 would allow an animal to break free should it become entangled. The tags relayed GPS locations with
80 a positional accuracy within 5 m through an Argos satellite link every 30 minutes, along with
81 temperature and information about tag movement and diving rates. The actual distance of the satellite
82 antenna from the manatee varied with the size of the manatee and behavior, but at a minimum, the tag
83 would be at the surface at all times when the manatee was <2m below the surface at slow travel
84 speeds, such as during feeding or resting. In deeper water, the tag could fix a GPS location and/or
85 transmit when the manatee surfaced to take a breath, typically every 2 to 10 minutes depending on
86 behavior (Hartman 1979).
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87 Data Analysis
88 To delineate specific habitat and movement corridor use by manatees, GPS points from all manatees
89 were combined into one GIS point layer in ArcMap 9.2 (Redlands, CA: Environmental Systems
90 Research Institute). First, the GPS point data were retrieved from each tag, and filtered temporally to
91 exclude times when the tags were not attached to the animals. Speed and positional filters were then
92 applied to eliminate spurious locations.
93 Travel speed
94 The GPS points were converted to travel paths using the ArcMap utility Points to Lines (Rathert
95 2004). The length of each line in meters was measured and added to the attribute table using ArcMap
96 utility Xtools Pro (V.7.0.0; Data East LLC, Novosibirsk, Russia). The polyline file was then merged
97 with the original point file, so that the attributes of each travel line were based on the second of the
98 two points used to draw the line. This second-point assignment associated the information of the
99 manatee’s destination with the travel. A final two columns were then added and calculated – travel
100 time (GPS fix time of the second point minus the GPS fix time of the first point) and travel speed
101 (length divided by time).
102
103 Based on our knowledge of manatee behavior, the travel paths were subdivided into three groups.
104 Slow speeds <1kph were designated as local use movements, typically foraging, drinking,
105 thermoregulating at warm water sites, or resting. Moderate speeds ≥1kph and <2kph were
106 designated as slow travel, which might occur during transit between local use sites. Fast speeds
107 ≥2kph were designated as fast travel, which typically occur during long-distance movements.
108 Each group of travel speed lines were converted to a density surface using the ArcGIS function
109 “Line Density”, which is based on the quadratic kernel function described in Silverman (1986, p. 76,
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110 equation 4.5). The density surface was calculated on a raster with cell size of 100x100m, over the
111 entire extent of the NGOM GPS data, with a search radius of 500m. For display purposes, areas with
112 densities of less than two travel paths were deleted. The remaining raster cells were displayed on a
113 quantile scale to highlight areas with higher travel densities. Local use movements were displayed on
114 top of the faster travel paths to better show the extent of habitat use.
115 Seasonal travel
116 To show the overall pattern of seasonal movements of the tagged manatees, the data were divided into
117 four seasons, with all years combined. The seasons were: winter = Dec-Feb, spring = Mar-May,
118 summer = Jun-Aug, and fall = Sep-Nov. Movements during each season were displayed on
119 individual maps.
120 Diving ratio
121 Each manatee tag contained a sensor that recorded the time and duration of each dive. It has been our
122 experience that manatee diving behavior is correlated with functional habitat use, such that no diving
123 to short duration diving is consistent with surface resting, or indicates water that is too shallow to
124 submerge the tag (<2m). Dives of a moderate duration of a few minutes each coupled with short
125 surface periods are consistent with foraging on submerged vegetation. Long duration dives of 5 - 20
126 minutes each are consistent with bottom resting, or fast travelling. Long diving durations coupled
127 with fast travel speeds indicate that the tag is being pulled under the surface and not necessarily
128 indicative of diving behavior, so all analyses of diving were performed only on periods where the
129 travel speeds were <2kph.
130
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131 To analyze diving behavior relative to location, all diving records between slow movement rate
132 locations were aggregated into a ratio of time spent on the surface over the time spent below the
133 surface. This “surface ratio” was log-transformed, and the resulting values were divided into five
134 equal bins. Data from the first (short dives), third (moderate dives), and fifth (long dives) quintiles
135 were selected and analyzed for display with the same procedure as the travel speeds.
136 Movement relative to seagrass beds
137 Manatees spend much of their time feeding in seagrass beds. To determine the potential for exposure
138 of the tagged manatees to oiled seagrass habitat, we combined the SCAT oiled shoreline data with the
139 seagrass location data. With the understanding that any oil that impacted a shoreline would have to
140 travel over nearby seagrass beds, we coded each seagrass bed that was <200m from any shoreline that
141 was surveyed for oil with the oiling category from the closest SCAT survey point. We then examined
142 each seagrass bed for slow-moving manatee tracks that occurred there, indicating possible foraging on
143 submerged vegetation. For each slow moving manatee track that intersected a seagrass bed, we noted
144 whether the track occurred before, during, or after the oil spill.
145 Results
146 Seasonal movement patterns
147 Data from the tagged manatees showed a strong spatial movement pattern related to season. During
148 the winter months, ambient water temperatures in the NGOM regularly fall below the ~20 °C
149 threshold that is considered to be tolerable for most manatees (Irvine 1983). To survive,
150 manatees in the region spend these cold periods in discrete warm-water sites such as Wakulla
151 Springs at the headwater of the Wakulla River, or the spring-fed rivers within the
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152 Crystal/Homosassa complex. During the spring season, the tagged manatees were generally
153 found to be migrating northwest from the warm water sites (Fig. 4). This pattern continued into
154 summer, when the tagged manatees were distributed all the way from Mobile Bay to the
155 Suwannee River (Fig. 5). Spring and summer were the seasons where the Deepwater Horizon
156 spill occurred, so the movements across the gulf from Apalachicola Bay to Mobile Bay would
157 have occurred at the same time and general location as the oil from the spill. In 2010, manatees
158 were sighted in Mobile bay as early as April, with several sightings reported in May (Ross and
159 Carmichael 2011). During the fall season, movements were typically west to east, as the animals
160 migrated back to warm water sites, which are not found west of the Wakulla River (Fig. 6).
161 Finally, during the winter months, most of the manatee movements were in or near the warm
162 water sites, with the exception of one individual (Harold) that was tracked to St. Joseph Bay
163 during a cold period in December, 2010, and was subsequently rescued and sent to a
164 rehabilitation facility (Fig. 7).
165 Local use and travel patterns
166 The patterns of local habitat use and travel paths were markedly different between the western part of
167 the study area from Mobile Bay to St. Joseph Bay and the eastern part from Apalachicola Bay to
168 Crystal River. In the western part, manatee travel was confined to a very narrow band close to the
169 shoreline, or within the Intracoastal Waterway (ICW). Local habitat use areas were found only within
170 Mobile Bay, or to a much lesser extent, other bays in the region (Fig. 8). By contrast, manatees in the
171 eastern part of the study area routinely travelled several kilometers offshore, with distinct local use
172 areas in and around Apalachicola, Ochlockonee, and Crystal River, the Wakulla River system, and the
173 mouths of the Aucilla, Econfina, Steinhatchee and Suwannee rivers (Fig. 9). The local use areas in
174 this region were coincident with large seagrass beds that have been mapped there (Fig. 10). The
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175 marked difference in the patterns of seagrass beds and manatee use found in the two parts of the study
176 area are both coincident with a difference in bathymetry: the western side shows a steep slope to
177 deeper water near shore, while the eastern side contains a wide shallow shelf that extends several
178 kilometers offshore (Fig. 11).
179 Oil spill interaction with seagrass beds
180 The NOAA SCAT surveys following the Deepwater Horizon spill covered all of the Gulf shoreline
181 from west of Mobile Bay to Ochlockonee Bay, and included large parts of the inland waters (Fig. 12).
182 The surveys were coincident with several nearshore seagrass beds in and around Perdido Bay,
183 Pensacola Bay, St. Andrew Bay, St. Joseph Bay, Apalachicola Bay, and Ochlockonee Bay (Fig. 13).
184 From St. Joseph Bay east, there was no oil observed in any of the SCAT surveys that were coincident
185 with nearshore seagrass beds (Fig. 14). West of St. Joseph Bay, most of the nearshore seagrass beds
186 were coincident with at least some oiled shoreline, though only small areas in Perdido Bay and
187 Pensacola Bay showed anything more than trace oiling (Figs. 15, 16). Tracking data showed that
188 manatees made slow movements over these beds that were consistent with foraging behavior, and one
189 tracked animal made these types of movements soon after the oil spill in a seagrass bed that was
190 adjacent to a heavily impacted shoreline (Zewie in October, 2010; Perdido Bay; Fig. 17). Other
191 SCAT survey data showed light to heavy oiling from west of Mobile Bay to St. Andrew Bay, but
192 these were along exposed shorelines that were not close to seagrass beds.
193 Diving patterns
194 Manatee diving patterns in the study area were consistent with expectations. Long diving patterns
195 were seen in deep water travel corridors. Manatee diving patterns in seagrass beds were moderate,
196 consistent with foraging, while some short dive patterns were seen in shallow interior waters. Mobile
197 Bay showed all types of diving patterns, with the long straight shipping channel in the center of the
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198 bay and the eastern bank showing only long dives. The mapped seagrass beds in the north of the bay
199 showed moderate dive times consistent with foraging, and also short dives consistent with very
200 shallow water or surface resting behavior (Fig. 18). The other panhandle areas with manatee use also
201 showed similar patterns of longer dives in travel corridors and on the outside of the barrier islands,
202 moderate dives in seagrass areas, and short dives in calmer inshore areas (Fig. 19). In the Big Bend
203 area near from the Wakulla River east, the pattern was different, consistent with the larger areas of
204 seagrass habitat and shallower, calmer offshore waters. There, longer dives were associated with
205 movements between local use patches that were generally associated with seagrass beds at river
206 mouths (Fig. 20). These local use patches showed moderate dive durations, with inshore waters again
207 showing low dive durations.
208 Discussion
209 The Marine Mammal Commission lists several mechanisms for direct and indirect injury of marine
210 mammals that have been observed from previous spills and studies
211 (http://mmc.gov/oil_spill/welcome.shtml). Direct effects can include inhalation of volatile organics
212 that cause respiratory irritation, inflammation, or emphysema, ingestion of oil that causes
213 gastrointestinal illness or systemic damage, or contact with oil that causes skin and eye irritation or
214 chemical burns. Indirect effects can include increased human response activity that disrupts foraging
215 and other habitat use and increases the risk of vessel strikes, and alteration of the marine environment
216 through reductions in biomass of marine mammal prey or seagrass, shifts in prey or seagrass
217 distribution, or contamination of prey or seagrass
218
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219 The most noticeable spatial pattern to emerge from the data is the striking difference between the west
220 and east sides of the NGOM study area. With a dividing line at approximately St. Josephs Bay, the
221 west side showed deeper water, less seagrass, faster manatee movements that were concentrated very
222 close to shore or in the ICW, and no local use offshore. In contrast, the east side showed shallower
223 water, more seagrass, and manatees that were more spread out with fast movements connecting
224 extensive local use areas offshore. These differences likely were critical factors in the potential
225 exposure of manatees in the NGOM to injury from oil during the Deepwater Horizon spill, which was
226 limited to the west side of the study area.
227
228 The physical characteristics of the western side of the study area may have contributed to a reduced
229 risk of direct injury from oil exposure. The greatest risk of exposure to manatees in the west side
230 would have been from travelling close to shore outside the ICW, or from foraging near the mouths of
231 Perdido and Pensacola Bays, which were both impacted with oil. Contact with oil would have been
232 less likely while manatees travelled through the protected ICW.
233 The risk of indirect injury from loss of habitat may also have been low on the west side, where there
234 were far fewer seagrass beds mapped offshore compared to the east side. Risk of vessel collisions
235 during recovery operations is an unknown risk factor, depending if vessels were operating in the
236 manatee travel corridors or further offshore. We were not able to find information on boat operations
237 in the study area.
238
239 No oil injured manatees have been documented from the Deepwater Horizon oil spill (Leslie Ward-
240 Geiger, Florida Fish and Wildlife Conservation Commission, personal communication). It is possible
241 that manatees were injured or killed by oil or recovery activity and were not detected. However, the
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242 unique combination of deep water close to shore preventing the establishment of exposed seagrass
243 beds, and manatee use of the protected ICW in the section of coastline that was impacted by oil, may
244 have reduced the potential for exposure of manatees to direct or indirect negative impacts. Had the
245 spill occurred closer to the Big Bend region, with its ample seagrass beds and high manatee use
246 offshore, the likelihood of a manatee being exposed to oil or indirect effects from recovery operations
247 may have been much greater.
248 Acknowledgements
249 Field support was provided by Susan Butler and Tim Green from the USGS Southeast Ecological
250 Science Center, and by Buddy Powell and Monica Ross from Sea to Shore Alliance. Funding for
251 analysis and publication was provided by USGS NRDAR. Use of trade, product or firm names does
252 not imply endorsement by the U.S. Government.
253 Literature Cited
254 Butler, S.M., P. Wilbur, G. Meigs-Friend and J.P. Reid. 2011. Documented Increase in Manatee Use
255 at the Wakulla River, FL. Poster presented at the 19th Biennial Conference on the Biology of
256 Marine Mammals, Tampa, FL., December 2011. URL: http://fl.biology.usgs.gov/pdf/IP-
257 033889_Final_Poster_(Butler).pdf
258 Deutsch, C. J., R. K. Bonde, and J. P. Reid. 1998. Radio–tracking manatees from land and space: Tag
259 design, implementation, and lessons learned from long–term study. Marine Technology
260 Society Journal 32:18–29.
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261 Deutsch, C. J., J. P. Reid, R. K. Bonde, D. E. Easton, H. I. Kochman, and T. J. O’Shea. 2003.
262 Seasonal Movements, Migratory Behavior, and Site Fidelity of West Indian Manatees along
263 the Atlantic Coast of the United States. Wildlife Monographs:1-77.
264 Deutsch, C.J., Self-Sullivan, C. & Mignucci-Giannoni, A. 2008. Trichechus manatus. In: IUCN 2011.
265 IUCN Red List of Threatened Species. Version 2011.2.
266 on 10 January 2012.
267 Fertl, D., A. J. Schiro, G. T. Regan, C. A. Beck, N. Adimey, L. Price-May, A. Amos, G. A. J. Worthy,
268 and R. Crossland. 2005. Manatee occurrence in the northern Gulf of Mexico, West of Florida.
269 Gulf and Caribbean Research 17:69-94.
270 Gunter, g. 1941. Occurrence of the Manatee in the United States, with Records from Texas. Journal of
271 Mammalogy 22:60-64. doi: 10.2307/1374684.
272 Hartman, D. S. 1979. Ecology and behavior of the manatee (Trichechus manatus) in Florida.
273 American Society of Mammalogists, Pittsburgh, PA.
274 Irvine, A. B. 1983. Manatee metabolism and its influence on distribution in Florida. Biological
275 Conservation 25:315-334. doi: 10.1016/0006-3207(83)90068-X.
276 Marine Mammal Commission (MMC). 2011. Assessing the Long-term Effects of the BP Deepwater
277 Horizon Oil Spill on Marine Mammals in the Gulf of Mexico: A Statement of Research
278 Needs. Downloaded from:
279 http://mmc.gov/reports/workshop/pdf/longterm_effects_bp_oilspil.pdf
280 National Oceanic and Atmospheric Administration (NOAA). 2010a. BP Deepwater Horizon Oil
281 Budget: What Happened To the Oil? (August 4, 2010). Downloaded from:
282 http://www.noaanews.noaa.gov/stories2010/PDFs/OilBudget_description_%2083final.pdf.
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283 National Oceanic and Atmospheric Administration (NOAA). 2010b. Shoreline Cleanup and
284 Assessment Technique. Downloaded from:
285 http://www.noaa.gov/factsheets/new%20version/scat.pdf
286 Pabody, C. M., R. H. Carmichael, L. Rice, and M. Ross. 2009 A New Sighting Network Adds to 20
287 Years of Historical Data on Fringe West Indian Manatee (Trichechus manatus) Populations in
288 Alabama Waters. Gulf of Mexico Science 27:52-61.
289 Rathert, D. 2004. Points to Lines V.2.1. downloaded from
290 http://arcscripts.esri.com/details.asp?dbid=12702.
291 Reid, J.P., G.B. Rathbun, and J.R. Wilcox. 1991. Distribution patterns of individually identifiable
292 West Indian manatees (Trichechus manatus) in Florida. Mar. Mamm. Sci. 7: 180-190.
293 Reid, J. P., R. K. Bonde, and T. J. O’Shea. 1995. Reproduction and mortality of radio-tagged and
294 recognizable manatees on the Atlantic coast of Florida. Pages 171–191 in T. J. O’Shea, B. B.
295 Ackerman, and H. F. Percival, editors. Population biology of the Florida manatee (Trichechus
296 manatus latirostris). National Biological Service Information Technology Report.
297 Ross, M. and R. Carmichael. 2011. Proposed data collection plan to assess injury to West Indian
298 manatees from the Deepwater Horizon Oil Spill outside of Florida. Downloaded from:
299 http://www.fws.gov/contaminants/DeepwaterHorizon/PreassessmentWorkplans/2010_06_09_
300 MAMMAL_Signed_errata_OutofFL_Preassessment Redacted.pdf
301 Silverman, B. W. 1986. Density estimation for statistics and data analysis. CRC Press.
302
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303 Tables
304 Table 1: Names and tracking information of manatees tagged in the NGOM. Manatees with data in
305 bold were tracked during the oil spill (n=10), those with underlined data were tracked only after the
306 spill (n=3), while those in regular font were tracked only before the spill (n=5).
Name Source Tagging Site Tag on Date Tag Off Date No. Days No. Fixes
Bama DISL Mobile Bay 04 Sep 2009 16 Jul 2010 315 13562
Bumpy DISL Mobile Bay 05 Sep 2009 27 Jan 2011 509 16202
Zewie DISL Mobile Bay 11 Aug 2010 12 Jan 2011 154 4926
Shelby DISL Mobile Bay 11 Aug 2010 29 Sep 2010 49 3797
Wilson DISL Mobile Bay 12 Aug 2010 16 Sep 2010 35 2491
Coontie USGS Wakulla River 02 Jun 2010 20 Jun 2010 17 637
CR018 USGS Crystal River 12 Jan 2009 16 Sep 2010 612 12269
CR505 USGS Wakulla River 14 May 2008 01 Jun 2008 18 759
Dash USGS Crystal River 23 Mar 2010 24 Jul 2010 123 3736
Ebb USGS Wakulla River 22 May 2008 04 Apr 2009 317 6476
Ellie USGS Crystal River 12 Jan 2009 15 Jul 2009 184 4708
Getty USGS Wakulla River 03 Jun 2010 24 Sep 2010 113 3993
Harold USGS Crystal River 19 Mar 2009 07 Dec 2010 628 10651
Izzy USGS Wakulla River19 Jun 2008 12 Oct 2010 845 20685
Texas USGS Crystal River 13 Sep 2007 20 May 2008 250 6853
TwoNotch USGS Wakulla River 09 Dec 2009 21 Aug 2010 255 6111
Zip USGS Wakulla River 08 Dec 2009 21 Jul 2010 225 4714
307
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308 Table 2: List of GIS Layers used to analyze potential manatee impacts from the Deepwater Horizon
309 oil spill.
Name Source URL
Backgrounds
Imagery ESRI World Imagery http://www.arcgis.com/home/gallery.html
Polygon Shoreline (nos-80k) NOAA http://coastalgeospatial.noaa.gov/shoreline.html
Place Names ESRI World Boundaries http://www.arcgis.com/home/gallery.html
and Places
Bathymetry NOAA http://www.ngdc.noaa.gov/mgg/bathymetry/hydro.html
Seagrasses
AL+FLSeagrasses USGS NWRC http://www.ncddc.noaa.gov/website/CHP/viewer.htm
SCAT Shoreline Survey
SCAT_Max_Oil_Houma_2011_0501 NOAA http://gomex.erma.noaa.gov/
MaxOiling_Mobile_Nov11 NOAA http://gomex.erma.noaa.gov/
Manatee Telemetry USGS and DISL NA
310
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311 Figures
312
313 Figure 1: Range of the Florida manatee and Antillean manatee in the Gulf of Mexico.
314 Solid line denotes areas with regular manatee occurrence, while dotted lines show areas
315 with occasional sightings.
316
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317
318 Figure 2: Study area from Mobile Bay, AL in the west to Crystal River, FL in the east, highlighting
319 some of the major habitat features used by Florida manatees in the northern Gulf of Mexico
320
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321
322 Figure 3: Florida manatee with tethered, floating GPS tag.
323
324
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325
326 Figure 4: After spending much of the winter at warm-water refuges at Crystal River and
327 the Wakulla River, some manatees in the NGOM begin migrating northwest during the
328 spring.
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329
330 Figure 5: Some manatees travel to Mobile Bay and points west from March throughout
331 summer
332
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333
334 Figure 6: Manatees return from summer habitat to their winter refuges in the fall
335
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336
337 Figure 7: Manatees generally remain close to warm-water refuges during winter
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338
339 Figure 8: A Kernel Density analysis was performed separately on slow and fast movement
340 segments. Fast travel movements are pink, and are displayed below slow, local use
341 movements, which are in blue and are displayed on top. Manatees travelling in the
342 panhandle remain very close to shore, or use the inland waterway
343
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344
345 Figure 9: Manatees in the Big Bend region range farther offshore, both for travelling and
346 foraging, compared to the panhandle area (see Fig. 8).
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347
348 Figure 10: A composite layer of known seagrass beds in Alabama and Florida shows large
349 seagrass beds in the Eastern part of the NGOM.
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350
351 Figure 11: The 3m depth contour is very close to shore in the panhandle, but farther away
352 in the Big Bend region. Manatees generally travel through relatively shallow water to
353 access their seagrass forage.
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354
355 Figure 12: After the Deepwater Horizon spill, much of the Alabama and Florida
356 Panhandle shoreline was surveyed for oil deposits (NOAA SCAT Survey)
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357
358 Figure 13: By intersecting the manatee movement, seagrass, and NOAA SCAT layers, a
359 composite layer of possible interactions between manatees and oiled seagrass areas
360 emerges. There are three main areas where this overlap occurs.
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MANATEES IN THE NGOM
361
362 Figure 14: The area with overlapping manatee use, seagrass, and shoreline oil surveys
363 farthest to the east was the region near Apalachicola. There was no oil observed in any of
364 these areas
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MANATEES IN THE NGOM
365
366 Figure 15: The three overlapping locations in the vicinity of Panama City showed trace
367 oiling. The two locations to the southeast were probably erroneously plotted outside the
368 bay due to differing shorelines in the GIS layers.
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MANATEES IN THE NGOM
369
370 Figure 16: The final overlapping area was in the vicinity of Pensacola. Here, most of the
371 overlapping areas were in the intracoastal waterways, so less oiling was found compared to
372 exposed coastline. Three areas were found to contain trace to heavy oiling during the
373 SCAT surveys.
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MANATEES IN THE NGOM
374
375 Figure 17: The overlapping area at the entrance to Perdido Bay that was found to have
376 oiled shoreline was visited by a manatee in October, 2010. The manatee made slow
377 movements that are associated with foraging.
378
379
380
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MANATEES IN THE NGOM
381
382
383 Figure 18: Manatee diving patterns as indicated by the surface ratio in Mobile Bay, AL.
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MANATEES IN THE NGOM
384
385
386 Figure 19: Manatee diving patterns as indicated by the surface ratio in and around St.
387 Joseph and Apalachicola Bays, FL.
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MANATEES IN THE NGOM
388
389
390 Figure 20: Manatee diving patterns as indicated by the surface ratio in and around
391 Ochlockonee, Oyster and Goose Creek Bays, and the Wakulla, Aucilla and Econfina
392 Rivers.
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