The year 2017 was not a good one for Florida's manatees.

A record number of manatees died after watercraft collisions in Volusia County during the year. Statewide, at least 538 manatees were found dead in waterways, the third highest year on record.

At least 13 manatee fatalities in Volusia County were attributed to watercraft-related incidents, according to an annual mortality summary from the Florida Fish and Wildlife Conservation Commission. The county tied with Brevard County for the second most boat-related deaths, just behind Lee County, where 16 manatees were killed.

The 39 total manatee deaths in Volusia County made 2017 the second highest number of deaths on record in the county. In 2013, 42 manatee deaths were reported. A large number of manatee deaths that year were thought to be related to massive algae blooms and sea grass die-offs in the Indian River Lagoon system, including Mosquito Lagoon.

Given the growing manatee population in Florida and the region, officials said an increase in the number of manatee deaths is not unexpected.

"There's definitely a growing number of manatees," said Debbie Wingfield, manatee protection program manager for Volusia County Environmental Management. "With that, you are going to have more deaths for all types of reasons, whether you're talking cold stress, boat-related or natural causes."

Only one manatee death — an infant — was reported in Flagler County last year.

The 538 manatees found dead in Florida waterways was also the most since 2013.

Red tide algae blooms were identified "as a significant contributing factor" to the overall manatee deaths, said Michelle Kerr, a public information specialist for the Wildllife Commission's Fish and Wildlife Research Institute. Other than the red tide deaths, the deaths attributed to other causes "appear to be within normal parameters," Kerr said.

Statewide 106 manatee deaths were attributed to watercraft collisions. Overall, Kerr said watercraft-related collisions account for about 20 percent of the manatee deaths over the past five years.

That's a little lower than Volusia County, where about one-third of the manatee deaths are attributed to watercraft-related incidents. Numerous seasonal boat speed limits are in effect across the county to protect the manatees in areas where they're known to congregate.

The Wildlife Commission doesn't use its manatee mortality statistics to draw conclusions about the state's manatee population.

"We do not like to compare mortality numbers with population numbers," said Martine de Wit, a wildlife commission manatee veterinarian.  "The way we use the data is to look at trends from a health perspective."

That's in part because the only population information is gathered during an extreme cold period once a year, when manatees are gathered at warm water refuges around the state.

During the rest of the year, manatees travel all across the state, said de Wit. Scientists don't have as much information about where the manatees go and what they're doing when they're on the move.

The cause of death couldn't be determined in 159 of the total deaths last year. De Wit said in most of those cases the cause of death couldn't be determined because the manatees could not be examined because their bodies were too decomposed. 

For example, perinatal deaths are always high in Brevard County. "We tend to believe it's a popular birthing ground for manatees," she said. "But unless we know how many are born, we can never tell for sure."

Brevard County led the state with 111 manatee deaths last year. At least 17 of those were thought to be related to the lingering issues in the Indian River Lagoon, said de Wit.

Floridians who remain concerned about manatees should consider buying manatee license plates, said Kerr, because proceeds from the sale of those state license tags continue to support manatee research and conservation across the state.