2022 Manatee Mortality Data - Background Information
Overview
Fish and Wildlife Research Institute staff perform a necropsy on an adult female manatee carcass that was reported in the week after Christmas on Egmont Key. The preliminary cause of death is cold stress.
The total statewide manatee mortality number (800) for 2022 was above the 5-year average (741) of the most recent years but was lower than that of last year (1,100). Mortality was high due to the ongoing Unusual Mortality Event (UME) from starvation and malnutrition on the Atlantic coast. The main difference with the higher total statewide number of 2021 was that there was a) no largescale red tide-related mortality on the Gulf coast in 2022, and b) lower number of verified carcasses in the Atlantic coast UME in 2022. Cool temperatures have a negative effect on manatees compromised by malnutrition, causing this UME to spike during winter. It is possible that a relatively warm December 2021 and less cold days in winter 2021-2022 contributed to lower mortality from starvation in early 2022. The number could also be lower if the population size decreased, after the unprecedented mortality in 2021 left less manatees to die on the Atlantic coast. Another uncertainty is carcass detection, if there is different distribution of animals between years, less carcasses may be noted when these occur in remote areas.
Leading causes of death
To manage increasing workload and carcass numbers, a significant number of carcasses is not fully necropsied. These include carcasses in remote locations or carcasses that are badly decomposed, for which a cause of death is not expected to be determined. Carcasses may still be partially examined to aid specific health investigations. More information on carcass sampling and details on how this is implemented in the Atlantic UME investigation can be found in the article Carcass examinations in the Atlantic Unusual Mortality Event. When excluding undetermined causes and carcasses that were not fully necropsied, mortality from starvation and chronic malnutrition was the leading cause of death during the cooler first three months of the year. Since April, watercraft-related mortality was the most common cause accounting for almost half of all known causes statewide. Similarly, these two causes were also leading among live rescued manatees.
Other findings of interest
FWC Marine Mammal Rescue Team rescue an entrapped manatee from a retention pond system in Lee County after Hurricane Ian. Activities conducted under U.S. Fish and Wildlife Service permit #MA770191.
Researchers documented nineteen (preliminary number) manatee carcasses that were crushed, impinged, or drowned in water control structures and navigational locks. This is the highest yearly number on record since the start of the manatee mortality database in 1974. The FWC performs a detailed investigation into every mortality reported near a structure. The 2022 mortalities occurred at nine different structures. Over the years, manatee protection measures and retrofitting these structures with protection devices have resulted in safer passage, but most of this year’s mortalities occurred at structures without manatee protection. It is possible that changes in manatee distribution now cause higher traffic through structures and locks that previously did not encounter many animals. Flooding can also change operation of water control structures. FWC and USFWS continue to work closely with structure managers to address and reduce such deaths. At least eleven live manatees were successfully rescued and released from entrapment by water control structures.
No mortalities were definitively attributed to hurricanes Ian and Nicole. Such a cause is not likely determined through necropsy alone and requires circumstantial evidence that is often lost by the time response is available. There was no increase in reported and verified carcasses after the storms, but FWC staff and partners rescued five manatees that had become entrapped after storms floods receded.