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Manatee Migration Update: March 15, 2000

Today's Report Includes:

Brian and Calista Released! Field Notes from Biologist Cathy Beck:

"Dear Students,
All's well with our manatees! The release of Brian and Calista went very well on March 1. Although no manatees were in Blue Spring Run at the time of the release, they apparently were hiding nearby. As expected, a few came over to 'see what was going on' and Calista and Brian quickly teamed up with others.

"Within a few days, both made their way to Lake Beresford, albeit separately. Brian then moved to Lake Monroe on 3/7, where he stayed until 3/9, when he plotted to the north in the St. Johns River near Hontoon Island. Calista also moved from Lake Beresford toward Lake Monroe on 3/7, arriving on 3/9. By 3/10, she showed a move to the south end of the lake.

Xoshi Dodges Speeding Boats
"Since the last report, Xoshi moved north (downriver) in the St. Johns River. Susan and Dean caught up with her on 3/1. She was adeptly dodging and diving away from the many fast-moving boats in that part of the river. Susan reports that she was very glad to see Xoshi avoid the boats so well, because the river was very crowded and, despite slow-speed zones, most boats were speeding.

"By 3/3, Xoshi had made a turn back toward the south and was plotting in Lake Dexter. Lake Dexter is not heavily used by boats, as there are no marked channels in the lake! Xoshi has remained in Lake Dexter since then. On 3/8 Susan and Dean observed her feeding and cavorting with up to 10 other manatees. Very good news!

Challenge Question #10
"In addition to boat collisions, what are the other risks that cause disease or death to manatees. Which ones are 'natural causes', and which ones are 'human-related?' Which risks cause the most manatee deaths? The least?"

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

"Comet is still using the eastern side of Lake Monroe, where there are substantial beds of vegetation. Susan and Dean checked on him again on 3/2, when he was still with another manatee and apparently enjoying this site! As of 3/10, he continues to use Lake Monroe.

"The weather continues to warm here, and Ivan moved South to the mouth of the Chassahowitzka River on 2/29. As of 3/10,Ivan continued to stay in that area. There are excellent seagrass beds there and he is no doubt feeding.

"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."

Cathy Beck
Sirenia Project
Gainesville, FL

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

What Do Boat Numbers Mean for Manatees?

Boat Registration Graph
(Click to enlarge)
Courtesy of Save the Manatee Club

Florida officials have compiled manatee data over the last 23 years, from 1976 to 1999. Based on that data, a graph of boat registrations and manatee deaths from boat collisions has been prepared. Study the graph and then answer:

Challenge Question #11:
"Describe the pattern or trend in this graph. What can you conclude about the relationship between the number of boat registrations and manatee deaths?"

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

Try This Activity and Have a Contest!
Divide your class into groups and have them think of ways to protect the manatees from boat injuries. Be creative!
  • Can you think of any new inventions that might help protect manatees?

  • Is there a way to move a boat through the water without endangering manatees? (For example, how might you design a propeller guard?)

  • There already are some boating laws and signs to help protect manatees. Can you think of ways to make these more effective?

  • Send your innovative ideas and we may share them in a future report. Write to jnorth@learner.org

Manatee Math Challenge: Ranger Wayne's Roll Call

Ranger Wayne Hartley

"I'm sending all of my datasheets to you this time because they were so easy to fill out--no manatees! Actually I felt it was interesting that although the temperatures were about the same throughout, especially the river temperature, the manatees reacted to very small changes."

Challenge Question #12:
"Looking at the data, what dates did the manatees react to 'very small changes' in river temperature? For those dates, can you tell Ranger Wayne how much the temperatures changed? And what were the manatees' reactions?"

Here's the latest data from Blue Spring:

Date

Air Temp High(C)

Air
Temp
Low(C)

River Temp (C)

Run Temp. (C)

# of Manatees

02/25 10 27 19.1 22.5 8
02/26 10 29 19.6 nt 6
02/27 12 30 20.9 nt 5
03/01 9 30 21.5 nt 0
03/02 13 29 21.6 nt 0
03/03 16 30 22 22.8 0
03/04 15.5 30 22.1 nt 0
03/05 9 27 21.6 nt 1
03/06 6 26 21.1 nt 2
03/07 11 30 21.3 22.6 3


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

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

What's So Special About Blue Spring? Discussion of CQ #6:
Biologist Cathy Beck explained the reasons for releasing the manatees at Blue Spring, instead of some other location:

"The St. Johns River area around Blue Spring State Park provides a very good habitat for manatees. There is abundant aquatic vegetation, which supports an existing resident population of wild manatees. In addition, during cold weather the warm spring water offers a safe and natural winter refuge for manatees. Blue Spring also has a good 'track record'. Other rehabilitated manatees released here have done very well."

Listen to Manatees: Discussion of CQ #7
Have you ever wondered what a manatee vocalization sounds like? Here's a sampling courtesy of U.S. Geological Survey's Sirenia Project:

Listen to a Manatee

Thanks to all the classes who sent in their answers to Challenge Question #7 about "Why do you think manatee vocalizations are delicate and high-pitched?" Sirenia biologists Cathy Beck and Bob Bonde explained why this is:

"Manatee squeaks and chirps are relatively high pitched, and are probably so because the manatee has a very unique apparatus for optimally hearing best in that frequency range. (Their hearing is limited in the lower ranges to < 1000 Hz and the upper ranges to about 50-60 KHz.) That frequency range is limited by intensity and distance, and we suspect only effective in relatively close quarters.

"A manatee's actual hearing range would be very hard to predict, however, because hearing distances are based on several usually environmental conditions (depth, salinity, vegetation, surface refraction, wax in your ears, etc). Under ideal circumstances we would guess that they can hear vocalization sounds only within 10's of feet (maybe to 100'). (But I have seen them respond to jet skis that were over a mile away. If the sounds are louder--higher dB, or more energy--then they can hear them farther away.)
"Manatee vocalizations are meant to be heard for short distances. That's mostly a result of their environment, since there is no need to communicate in the open ocean. (Compare this to a whale vocalization, that is thought to be heard many miles away and serve as long distance communication.)

"To this day, no one really knows how the manatee sounds are generated in the auditory tissues of the cranium. Unlike cetaceans, manatees do not have an extensive array of sinuses where air is passed between the membranes to produce the desired sounds, and they do not have traditional vocal chords.

"What sound like simple chirps or squeaks to us, when recorded and slowed down, are actually all very different and apparently the manatee's perceptual ability to differentiate modulations within each sound is very incredible. Our computers (brains) can only detect very striking differences in the sounds, whereas manatees are actually sending very unique auditory signatures that, for example, allow the mother to differentiate her calf's sounds from all the other manatee and ambient sounds in the environment. There is a great need to do an MRI on a manatee head so that we can start to understand how vocalizations in manatees really work! The issue of infrasonic communication in sirenians is another matter and still only theoretical."

A Fat Question: Discussion of CQ #8
In Challenge Question #8 we asked why a Manatee cannot tolerate cold water as well as a whale? Here are a few of your responses:

"I think manatees have to go in warm water and whales don't because whales are much bigger and have way more blubber than a manatee. Therefore they can withstand the colder temperatures better."
(KitKat2V@aol.com)

"A manatee has a thin layer of fat, and a whale has a heavy layer of fat." Sean Maguire, (Sean_Maguire@wiscasset.k12.me.us)

According to Cathy Beck, "whales have a thick layer of blubber under their skin that insulates them from the cold water. Although manatees have a layer of fat under their skin, it is never as thick as a whale's blubber. Also, like you and me, their fat can vary in thickness depending on how much the animal has been eating. If there have been several cold spells and the manatees have not eaten often, the fat layer becomes thinner; then the manatee is less able to tolerate the cold water. It would be like you going out to play in the snow without a jacket!"

Try This!--It's Really "Cool"!
Manatee expert Bob Bonde and whale expert Ann Smrcina offer this experiment to help you test "first hand" why cold feels different to a manatee than it does to a whale. This may be a bit messy, but the experience is worth it!

Coming This Friday: Answers from the Manatee Expert
Nancy Sadusky of Save the Manatee Club has answered your Sirenia inquiries, and her answers will be posted this Friday!

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: jn-challenge-manatee@learner.org
2. IMPORTANT: In the Subject Line of your message write: Challenge Question #10 (OR #11 OR #12)
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 March 15, 2000

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