Despite being 10–12 feet long and weighing 1500–1800 lbs, Florida manatees aren’t always easy to find. The aerial surveys that are relied on to conduct annual counts are expensive and criticized for sometimes under or over-estimating sea cow numbers. In addition, the flights can’t always cover the vast water networks that manatees roam in search of warmth and food. Weather conditions and water visibility can also interfere with the results. Last year, the US Fish and Wildlife Agency downgraded the status of manatees from endangered to threatened – in part because annual surveys reported higher numbers. Conservationists have objected saying accurate surveys are critical to effectively manage the species.
The US Geological Survey researchers have now found something easier to locate: DNA. By creating a new DNA marker, the presence of manatees can be detected in waters where they may not easily be spotted.
“It doesn’t tell you necessarily how big the population is, but it detects the presence,” said geneticist Maggie Hunter, who helped develop the marker and was lead author on the paper published in Endangered Species Research.
Like humans, manatees shed cells in their environment, leaving behind a trail of DNA. This environmental DNA can be detected for 2–4 weeks. In addition to locating hard-to-reach places where manatees might congregate, DNA testing can also track travel corridors as they move about seasonally. Manatees take up residence primarily in Florida’s coastal waters during winter. Some individuals migrate as far north as the Carolinas or as far west as Louisiana in summer. In recent years, manatees have swum as far north as Cape Cod, Massachusetts.
The DNA testing method could also be extended for use in places where manatees are scarcer and resources tighter. A subspecies in Cuba numbers about 100, but next to nothing is known about them. And in Brazil, dark water in the Amazon makes it nearly impossible to find Manatees by aerial surveys.