This blog was created to allow
the public to follow two manatees, Rita and her calf Georgie, as scientists
track them after their release back into the wild. Please return for weekly
updates.
NOTES FROM THE FIELD – WEEK
5:
17-May-2012
Scattered thunderstorms
prevented Willie, Beth and Kendria from going out early to check on Rita and
Georgie but finally by 4pm, the rain had held up just enough to search for the
tagged manatees. After traveling for over 70 miles around Great Harbour Cay to
the south and back, they had safely returned to Bullock’s Harbour. We found
them with the adult and juvenile male and observed them feeding on seagrass
beds. Georgie remained very close to her mother, Rita, as they were feeding and
socializing with the other manatees.
We are able to track the
manatees using two methods: signals received using a VHF radio receiver and
through locations derived from satellites passing overhead. These can be
downloaded from Argos’ website throughout the day and, unlike the radio
receiver isn’t dependent on us being within receiver range of the animals which
isn’t always possible because of bad weather conditions. If the animals are not
within radio range, using a combination of both methods can be best; first
check the Argos location, then travel to the general area and use the VHF
receiver to actually find them.
Argos categorizes satellite
locations received from their tags by ‘quality code.’ These codes are
essentially a measure of location (latitude and longitude) accuracy. Accuracy
is affected by how much of the tag’s transmitter is above the water’s surface
as a satellite passes overhead and also how many satellites passing overhead
picked up the same transmission. Accuracy can range from 100 meters to tens of kilometers
so close attention must be paid to the quality code (Deutsch et al. 2003).
Works Cited
Deutsch, C. J., Reid,
J. P., Bonde, R. K., Easton, D. E., Kochman, H. I., & and O'Shea, T. J.
(2003). Seasonal Movements, Migratory Behavior, and Site Fidelity of West
Indian Manatees Along the Atlantic Coast of the United States. The Journal
of Wildlife Management: Wildlife Monographs 151 , 1-77.
18-May-2012
Early morning Argos satellite
locations and strong VHF radio signals indicated that Rita and Georgie were
still in Great Harbour Cay harbour.
Frenchie, Willie and Kendria
decided to search for the manatees by foot. Strong VHF radio signals lead them
to the entrance of the marina. Using our binoculars, we found both tagged
animals in an area just outside of the marina. Manatees are occasionally seen
congregating here to feed and rest.
 |
| Rita and Georgie |
Unlike other marine mammals,
manatees don’t form social groups. They are often described as semi-social
animals that are known to congregate in areas where they can share common
resources such as food, water, shelter, and/or warmth. Although manatees may
travel together, these groups are only temporary and associations don’t depend
on sex or age class. The most basic social unit exists between mother and calf.
There are two female mother-calf pairs here in the Berry Islands, Rita and
Georgie and Gina and JJ.
 |
| Gina and JJ |
Resource:
19-May-2012
Using the H-antennae and the VHF
receiver, Kendria checked to see if she was able to pick up VHF signals from Rita’s
tag in the marina. On open water, VHF signals can be heard within a 9 miles
(15km) radius. When tracking from land we have to consider landmasses obstructing
the signal.
We weren’t able to pick up a
tag signal from neither Rita nor Georgie from the marina. Willie and Kendria
then headed out to search for them in the harbour. We were able to pick up a
signal close to the causeway that connects Great Harbour Cay to Bullocks
Harbour and separates the harbour from mangroves. Although a tight space, the resident
manatees from Great Harbour are known to swim under the causeway and spend time
resting in the mangroves on the other side. It seems Rita and Georgie have now learned
to use this area as well.
20-May-2012
 |
Penny, Frenchie’s
dog, spent a few days
assisting us in our tracking efforts.
|
Pulse signals emitted from
their VHF tags indicated that Rita and Georgie were nearby and possibly in the
marina. Kendria and Penny went to search for the tagged manatees by
foot.
There are a few areas that the
manatees are known to visit once they’re in the marina area.
- The Marina Office: The marina office has an ice machine that leaks fresh water. Although an artificial source, the manatees do enjoy this reliable water source.
- The rocks lining the north side of the marina: An important feeding area, the manatees are known to spend hours moving along the rocks feeding on moss and algae.
- The Mangroves: There are two mangrove systems located in the marina. One is at the elbow of the marina and the other is at the eastern end of the marina. These areas provide a safe place to rest and may also serve as a source for freshwater.
- The ‘T-Canal’: This area was highlighted in week 4 field notes .
- Under the Townhouses: The townhouses lining the north side of the marina provide both shelter and water to the manatees. The manatees can be seen traveling under the townhouses to get in and out of the marina and also getting water from leaking pipes from the reverse osmosis systems under each townhouse. Of particular interest is under a local fisherman’s, Al’s, dock; the manatees can be found regularly under this dock feeding and resting. Visually, there is nothing special about this area compared to other areas in the marina but the manatees certainly enjoy this spot in particular.
 |
| Rita feeding on algae. |
Today shortly after 10am, Rita
and Georgie were found at Al’s dock feeding on algae on the pilings. Visitors
stated that they saw the two tagged manatees there since the early morning
hours. Although they were in the same vicinity, Rita and Georgie spent most of
the time feeding separately. Georgie was observed nursing and getting water
from a leaking pipe.
As a treat, two nurse sharks
were also seen in the area! Yikes!!
 |
| Georgie created a huge sediment bloom while she was feeding on the sea floor. She then moved to a nearby piling to indulge in some delicious algae! |
21-May-2012
Rita and Georgie continue to
travel in and out of the marina and spend time feeding in the harbour.
On average manatees can
consume 10-15% of their body weight in food in one day!
Manatee
ID
|
Body
Weight* (lbs)
|
Estimated
food intake (lbs)
|
Rita
|
1042
|
937.8
- 885.7
|
Georgie
|
388
|
349.2
- 329.8
|
*Body
weights were taken during a health assessment conducted on 06-March-12 by
Dolphin Cay-Atlantis staff while still in captivity.
Resources:
22-May-2012
Rita and Georgie were first
sighted by tourists docked in the marina. They spent the morning feeding on
algae lining the pilings and resting in various dock slips.
 |
| Top photo: Rita resting in the marina. Bottom photo: Rita traveling under the docks to feed on the pilings. |
23-May-2012
 |
| An attenuator |
Using the H-antennae and
receiver, Kendria was able to pick up loud VHF signals from Rita’s tag. Attenuating
at 100dB, the loud signals meant that the tagged manatees were either just
under Kendria or Rita’s tag was no longer attached to her belt. An attenuator
is used to decrease the power of the tag signal received and narrow down on
a direction in which the tag is located.
At 1:27 pm,
Kendria received a call from that marina office saying that Rita was sighted
but without a tag. Kendria quickly went over to check on her and Georgie. Both
animals seemed to be in good health with no visible wounds on them. Both Rita
and Georgie’s tag have a weak link that will automatically break if the tags
get caught or tangled. Within the next half hour, Willie and Kendria attached a
temporary tag on Rita’s belt. We later found her original tag in the marina and
attached it back to her belt safely.
The tagged
manatees remained in the marina until 5pm and were last seen swimming under the
dock towards the harbour.
A plot of the locations of Rita and Georgie via Argos
satellite shows their fifth weeks' movement around Great Harbour Cay; arrows
indicate direction of travel from Great Harbour Cay harbour to Lignum Vitae
Cay.
