Skip to main content

New Study Shows Impact of Watercraft on Manatees

manatee in water with scars

FWRI researchers examined 10 years of Florida manatee necropsy reports to characterize and quantify watercraft-related scarring. The researchers found that one out of every four adult carcasses analyzed in their study bore evidence of 10 or more watercraft strikes. With only 4% of adult manatees devoid of watercraft-related scars, it appears exceedingly rare for an adult manatee to not be struck multiple times in its life. This study shows that manatees are subjected to more sublethal watercraft strikes than any other studied marine mammal and it underscores the need for continued long-term vigilance in conservation actions in Florida.

Here in Florida, manatees share the waterways with hundreds of thousands of watercraft. A leading human-related threat to the manatee is collisions with watercraft, which account for 20−25% of reported mortalities.  Collisions with manatees can cause both sharp and blunt force trauma, and either kind of injury can result in death. Manatees also survive many encounters with watercraft. The goal of the new study was to advance understanding of sublethal watercraft-related impacts on the Florida manatee.

FWRI researchers demonstrated that sublethal injuries from watercraft collisions varied with life stage, sex, and region during the 10-year period of analysis (2007-2016). As expected, the number of scar patterns was greatest in adults, followed by subadults and then calves, which have had the least time to accumulate scars. Adult females had more scar patterns than adult males. Manatee carcasses recovered in and around Everglades National Park showed substantially fewer scars from watercraft collisions than manatees found in more urbanized areas. The long-term consequences of sublethal injury resulting in scarring are not fully understood, but short-term consequences include pain, elevated stress responses, and behavioral changes, as well as increased energy expenditure. Longer-term impacts could include decreased mobility due to healing of fractured bone, decreased swimming efficiency if large portions of the fluke are lost, compromised immune function and, if reproductive systems are damaged, decreased reproductive output. The researchers note that not all watercraft strikes leave permanent scarring, so the percentage of manatees hit could be even higher.

Read the full study:
Quantifying sublethal Florida manatee−watercraft interactions by examining scars on manatee carcasses.


GO SLOW, LOOK OUT BELOW—Make a Difference for Florida’s Manatees

More information on how vessel operators can protect manatees: