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Manatee Migration Update: March 29, 2000

Today's Report Includes:

Grabbed by a Gator! Field Notes from Cathy Beck

Photo courtesy of the Birmingham Zoo
"Dear Students,

Xoshi's transmitter had to be replaced, after it was grabbed by an alligator! A gator's strong jaws and teeth punctured the transmitter housing, and the high frequency signals to the satellite abruptly stopped. Suspecting what might have happened (because it's happened to our tags before) Dean and Susan traveled to Xoshi's last known location.

"The VHF part of her transmitter was still working so Dean and Susan were able to locate her by VHF. Xoshi's transmitter was still attached to the tether, and the tether to her belt, so I guess this gator let go pretty quickly, before the tether broke free.

"Susan and Dean removed Xoshi's damaged tag, and replaced it with a new one. But I don't want to give the impression that this was a simple task; it took Dean a few hours of swimming alongside her to accomplish the tag switch, while Susan kept a sharp lookout for gators!

Photo: U.S. Geological Survey, BRD, Sirenia Project
"Xoshi is doing fine now. On 3/21 Jim Reid observed her with Brian in Lake Woodruff, a National Wildlife Refuge. By 3/23, they had both moved south of Lake Woodruff in Norris Dead River, but Xoshi had moved a short distance away from Brian.

Challenge Question #13:
"Take a look at the picture of the manatee with a transmitter. If you were an alligator, and saw a manatee with a transmitter in tow, what would you be thinking about? Would you be interested in a very large manatee meal or the transmitter tidbit? Why?

(To respond to this question, please follow the instructions below.)

Troubled Transmitters for Brian and Calista?
"Current news on 3/27 was that Brian's tag is "off" (no signals), and Calista's tag hasn't moved - same location, no "tips". Susan is heading out to try to find them, and Jim will join her early Wed. if she is still out looking. We won't jump to any conclusions and I'll keep you posted.

Challenge Question #14:
"What reasons can you think of for Brian's tag being "off" (no signals), and Calista's tag being in the same location, no "tips"? (Be sure to read the information on transmitters below for clues)

(To respond to this question, please follow the instructions below.)

Comet and Ivan
"Comet remains in Lake Monroe. Since the last report he has traveled between the west and south side of the lake. Dean and Susan observed him for about an hour on Wed. 3/15. He was bottom resting in ~1m of water.

"Meanwhile, Ivan continues to use the area around the mouth of the Chassahowitzka River.

"I've sent the latest data for all the manatees, which you can look at below. Be sure to plot these locations on your map to track their latest movements."

Today's Satellite Migration Data
(Courtesy of U.S. Geological Survey's Sirenia Project)

Cathy Beck
Sirenia Project
Gainesville, FL

Tie a Belt Around Your Peduncle!
Click image for a better look
Cathy Beck's latest news about the transmitters may have you wondering. What do the transmitters look like, how do the scientists attach them to the manatees, what kind of radio signals are sent out, how long do they last, what is a 'tip' and what happens if the transmitter gets caught in something?

Journey North students tracking the migration of the Bald Eagle know that the eagle wears a "backpack" transmitter. Manatee transmitters, on the other hand, are attached with a "peduncle belt" and a "nylon tether." The belt goes around the manatee just in front of its tail, in an area called its "peduncle", and the tether is a stiff nylon rod (about 10 mm in diameter and 130 to 200 cm long) that connects the belt to the transmitter. Each tether has a "weak link" built into it, which will break and allow the manatee to swim free if the tether or transmitter ever become snagged on something such as a dock, a boat, thick vegetation, or even a hungry alligator!!

Radio Waves
The radio transmitters are contained inside of floating plastic cylinders about 39 cm long and 9 cm in diameter. The cylinders have a 20 cm wire antenna on the top of them, and every cylinder is color-coded with large identifying letters and engravings on them. Each cylinder actually has two different transmitters inside it. One is called a VHF transmitter which sends specific radio frequency signals to scientists in the field using a portable receiver. The other is called a Platform Transmitter Terminal or "PTT", and it sends out location signals to an orbiting satellite.

Typically, the PTT will send from two to six different location points for each tagged manatee every day. Besides "location" information, data is also sent on manatee "activity" (# of dives, duration of dive, # of times the transmitter "tips" greater than 90 degrees, i.e. swimming, playing, etc) and temperature.

According to Cathy Beck, satellite tracking data can be inaccurate or be interrupted for several different reasons. "The quality of the location plotted by the satellite varies, depending on whether the manatee (actually the antenna) is at the surface when the satellite passes--the antenna must reach the surface in order to broadcast the signal to the satellite. Also, data quality can be affected when there are a lot of structures or vegetation that may interfere with the signal."

Millennium Manatee Count
Dr. Bruce Ackerman
Two statewide manatee counts were conducted this winter by Florida Marine Research Institute (FMRI), with assistance from several state, federal, and county agencies, research labs and universities. Teams of airborne observers in small planes and helicopters counted manatees along both coasts, along with ground crews counting at power plants and other warm water sites.

Dr. Bruce Ackerman, a marine mammal biologist and coordinator of the survey, reported that 1,629 Manatees were counted during the first survey on January 16-17, and 2,222 were counted during the second survey on January 27, 2000.

Challenge Question #15:
"Take a look at the chart below of earlier census counts. How do this year's manatee counts differ from previous years? What reasons can you can think of for these different counts?"

Aerial Manatee Survey Results 1991 To 2000
(Courtesy of Florida Fish and Wildlife Conservation Commission's Marine Research Institute)

Date of Survey Total Count
Jan. 23-24, 1991 1,268
Feb. 17-18, 1991 1,465
Jan. 17-18, 1992 1,856
Jan. 21-22, 1995 1,443
Feb. 6-7, 1995 1,822
Jan. 9-10, 1996 2,274
Feb. 18-19, 1996 2,639
Jan. 19-20, 1997 2,229
Feb. 13, 1997 1,709
Jan. 29-30, 1998 2,022
Jan. 6, 1999 1,873
Feb. 23, 1999 2,034
Mar. 6, 1999 2,353
Jan. 16-17, 2000 1,629
Jan. 27, 2000 2,222

(To respond to this question, please follow the instructions below.)

Ranger Wayne's Roll Call: Blue Spring Season Ends

Ranger Wayne Hartley

"The season began on 5 November 1999 and ended on 14 March 2000. The ending was very feeble with hardly any manatees in during March but Paddy Doyle was in during regulation time for regulation reasons, the temperature in the river had dropped a little.

"We had 132 different manatees seen during the season, not counting the five captive releases. 115 spent the season and we had 12 calves. On 27 December 1999, my birthday, we had 112 for a single morning count. All of these are records, beating those set last year except for the morning count which beat a record of eighty-seven set two seasons ago. This year eighty-seven is boring!

"Twenty-nine manatees were hit by boats during the season. It was cool nearly all season so the boaters were not out much, so the count was down from forty last season. Unfortunately BS156, Twiggy, was killed in Lake Dexter on or about 4 March."

"Thanks to all the students for studying the manatees this year. It's been fun again.

"Here are the final data from Blue Spring ":


Air Temp High(C)


River Temp (C)

Run Temp. (C)

# of Manatees

3/13 6 31 22 22.3 0
3/14 11.5 27 21.6 nt 1
3/15 11 28 22 22.5 0
3/17 17 31 22.1 nt 0
3/19 19 30 22.1 nt 0

*(All temperatures are in degrees Celcius; "nt" = temperature not taken)

Wayne C. Hartley
Park Ranger
Blue Spring State Park

Manatee Math Challenge: Discussion of Challenge Question #12
Thanks to the students who answered Ranger Wayne's Manatee Math Challenge, and saw that the manatees had reacted to very small changes of only a .5 degree decrease in river temperatures on 3/5 & 3/6!

Katie Vernali carefully calculated the temperatures and number of manatees, and she noticed that March 5 was the first day the manatees reacted to this small change in temperature.

The Causes of Manatee Mortality: Discussion of CQ #10
Courtesy of Save the Manatee Club

Scientists break down the causes into six different categories:
  1. Watercraft collisions

  2. Flood gate or canal lock (crushed and/or drowned)

  3. Other human-related (deaths caused from monofilament line, litter, poaching, vandalism, culverts or other human-made structures)

  4. Perinatal (dependent calves under 4.9 feet [150 cm])

  5. Other natural (mortalities caused by natural circumstances such as cold stress or disease)

  6. Undetermined (the manatee is too badly decomposed to determine cause of death, the necropsy finding is inclusive, or the manatee carcass was reported and verified, but not recovered)

(Students identified many different causes of manatee deaths in their answers to CQ #10. In fact, we had so many answers that we just didn't have space to list them all. But, we put our special thanks to you below.)

Like Walking on a Busy Road Just to Breathe: Discussion of CQ #11

Boat Registration Graph
(Click to enlarge)
Courtesy of Save the Manatee Club
"Envision this, every time you need to breathe, you have to walk into the middle of a busy road in a dense fog. Now you have an idea of what many manatees face everyday of their lives.

"We are very concerned by the increasing trend in the number and proportion of manatee deaths caused by collisions with water craft" said Dr. James Powell of FMRI. Indeed, watercraft-related manatee deaths in 1999 set a new record of 82 deaths, surpassing last year's previous record of 66.

We asked you to focus on this problem in last week's CQ #11. You analyzed a graph of data about boat registrations and manatee deaths, and described any trends or relationships in the data.

Many students really set the trend with their careful answers:

"The more registered boats there are, the more manatee deaths. The higher the registered boats goes up, shown in green, the red manatee death line also goes up. When the registered vessel line is at its highest point, the manatees related death, shown by the linear trend black line, proportionately goes up." Iselin Middle School in Iselin, NJ (

"There is an upward trend. As the number of boat registrations increase so does the number of watercraft related manatee deaths. The more boats on the water the more manatee deaths there are. Also if there are more boats on the water it is more crowded. There is less room for the manatees and the boats have more of a chance of running them over. The waters are getting more crowded and the boaters don't watch where they are going and run them over."

"In the graph, both the number of boat registrations, and the number of manatee deaths or injuries, are on a large increase. I can conclude from looking at this graph, that both are related severely. The problem is that it doesn't seem that either one of them will start going down." DJ MAd DoG, Griswold Middle School in Rocky Hill, CT (

(Again, we're sorry we just didn't have space to list all the great answers, but we put our special thanks to you below).

Congratulations to all the students that worked so hard to answer Challenge Questions #10 and #11. Nice job!:
  • Sarah King, Griswold Middle School, in Rocky Hill, CT (
  • Christopher E. Flood (
  • Amanda Mantello, (
  • Katie Vernali (
  • DJ MAd DoG Griswold Middle School, in Rocky Hill, CT(
  • (
  • Kristina Anderson (
  • Ryanne Gannon, Allison Kasala,& Sumara Irshad, 7th Grade at Iselin Middle School in Iselin, NJ (

How to Respond to Today's Challenge Questions

Please answer ONLY ONE question in each e-mail message!:

1. Address an E-mail message to:
2. IMPORTANT: In the Subject Line of your message write: Challenge Question #13 (OR #14 OR #15)
3. In the body of the EACH message, give your answer to ONE of the questions above.

The Next Manatee Migration Update will Be Posted on April 12, 2000

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