Based on temperatures, can you find a trend in the number of manatees counted by Ranger Hartley at Blue Springs State Park? Once again this week, he's provided a snapshot of life at one of the manatees' favorite hotspots. Here's his report:
To: Journey North
"Two primary conditions effect the number of manatees present. The chief is water temperature. The colder the water in the St. Johns River, the more animals in the run.
"The other factor is timing. Their movements in response to temperature are not immediate. For example, if the manatees have been away during a long, warm period they may take several days to get back when the air turns cold. Therefore, counts on a cold day might be lower than expected. Similarly, the count on warm days after a very cold day may have more manatees. Also, they seem to sense the barometric change ahead of a large weather front, and come in ahead of it at times, no matter the water temperatures. Finally, we also see changes as the winter progresses. For example, during the first cold days in November the manatees respond more to cold than they do at this time of year.
"This is a very warm year. The spread between the cold night and warm day temperatures is 25 -30C, whereas normally temperatures range from 10- 15C. It seems that these warmer air temperatures have made the manatees more tolerant of cold water, so they haven't moved as much as in normal years.
Temperature and attendance graphs can show us what cold brings the manatees into refuges, what is comfort and what is life-threatening. At the end of the season, a story of the attendance sheets tells us who actually spent the winter and who just stopped by to get warm. These attendance sheets are important in another way. If additional restrictions are needed at Blue Springs to protect the manatees, the attendance sheets can five the factual backing to get the needed changes."
About Blue Springs State Park
The "run" enters the St., Johns River about 240 km upstream from its mouth. Manatees use Blue Springs only as a thermal refuge from the colder waters of the St. Johns River. They must leave the run to forage for food in the St. Johns River.