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Study Tracks Manatee Migration along Gulf Coast

Those chubby, lovable icons of marine conservation, West Indian manatees (Trichechus manatus), are a lot less sedate than you’d think, according to a recently published study by researchers at Alabama’s Dauphin Island Sea Lab.

Manatees are swifter than imagined, their numbers are growing, and they are as determined in their travel as the weekend stream on I-10.

Those were the observations published in June in the journal “Frontiers of Marine Science.”

The study synthesizes 10 years of data collected by Sea Lab researchers from satellite tracking and citizen-sourced sightings.

During migration, manatees have the potential to travel through a wide range of channel types and are exposed to a diversity of vessel types, including recreational boats, shrimp trawlers, barges and large container ships, the researchers found.

“More and more manatees are coming up from Florida during the summer time and using these ship channels as travel corridors. This means there’s more of a chance they’ll cross paths with a vessel of some kind, which makes them more vulnerable to boat strikes,” said post-doctoral researcher Carl Cloyed. “By knowing when they are using these channels the most, we can suggest the best times for channel maintenance and give recreational and commercial boaters a better idea of when they may encounter a manatee during the year.”

Manatees travel in both nearshore boat channels such as rivers, canals, and estuaries, as well as open water “fairways” like the soon to be widened and deepened Mobile Bay Ship Channel. But the creatures were found to use nearshore channels more frequently.

“Little research has focused on the use of nearshore channel types by marine mammals,” said the study, titled “Linking Use of Ship Channels by West Indian Manatees (Trichechus manatus) to Seasonal Migration and Habitat Use.”

Satellite-tracked manatees swam faster and moved more intently than previously thought in all channel types. The persistence indicated these channels as migratory and travel corridors.

“While well-documented historically in the north-central Gulf of Mexico, manatee sightings have drastically increased along the Alabama, Mississippi, and Louisiana coasts in warm months during the last several decades,” the study concluded.

“Increasing manatee population numbers in western and northwestern Florida may contribute to the increasing number of individuals migrating to the northern Gulf of Mexico during recent years.”

For the tagged manatees, GPS data included a total of 723 manatee days in the study area: 544 days in Alabama, 80 in Mississippi, 61 in Louisiana, and 37 in Florida. A total of 2,237 manatee sightings occurred from 2007 to 2017, including 1,945 sightings in Alabama, 205 in Mississippi, 79 in Florida, and 8 in Louisiana.

Researchers said their findings are “important information for managers, civil engineers, boaters, and the shipping industry to guide future conservation practices.”

“The northern Gulf of Mexico, and Mobile Bay in particular, can serve as a sentinel site that may be a ‘canary in the coal mine’ for assessing future boat-related risks to manatees and other migratory species.”

The decade-long study was funded by the National science foundation, the Alabama Division of Wildlife and Freshwater Fisheries, the Northern Gulf Institute, Mobile Bay National Estuary Program, and Dauphin Island Sea Lab.

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