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:
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).
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.
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|
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.
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!|
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!
Body Weight* (lbs)
Estimated food intake (lbs)
937.8 - 885.7
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.
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.|
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.