| MYTH #5: Boats only cause 25 percent of manatee deaths. This is insignificant considering most manatees are killed from other causes, such as cold weather. The state of Florida needs to focus on preventing the other 75 percent of manatee deaths. |
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FACT
There have been 4,672 manatee mortalities documented in Florida from 1974 – 2002. Of those, 1164 were attributed to watercraft collisions, 174 were attributed to flood gates or canal locks, 125 were other human-related, 967 were perinatal (dependent calf), 191 were natural cold stress, and 625 were other natural. For the remaining 1,426 carcasses no cause of death was identified: in the majority of cases, the carcass was too decomposed to determine a cause of death. The perinatal/dependent calf category is also not a cause of death, rather it identifies that the manatee died around the time of birth, the manatee was less than 150 cm (5 ft.) in total length and was determined to have not died due to human-related causes.(6)
Any species of animal living in the wild will suffer losses from natural causes and can usually overcome those losses. But the manatee population must also deal with a high number of additional mortalities caused by human-related factors. Because human-related manatee deaths are preventable, this area is the most logical place to begin in order to reduce mortalities.
Watercraft-related manatee mortality is the leading identified cause of manatee death in Florida. Most concerning is the fact that watercraft collisions is the leading cause of death of adult, reproductive age, manatees. Large mammals like the manatee, which have a long potential life span and slow reproductive rate, normally have a low adult mortality rate. Losing reproductive adult female manatees can be doubly lethal if they are pregnant or have a dependent calf.
Further cause for concern comes from recent research conducted at the Florida Marine Research Institute, which revealed that of the manatees whose carcasses had been recovered in the salvage program, few were living past the age of 30 and the majority of animals died between the age of 0 and 10 years, nowhere near their estimated life expectancy of 60 years.(7, 8)
Reducing adult manatee mortality is the most effective method to increasing the manatee’s recovery rate, and the reduction of watercraft-related mortality is the most productive and reliable means to reduce adult manatee mortality. Other causes of manatee mortality do not affect the adult age class in numbers as large or significant as watercraft mortality. Manatee population viability analysis and population modeling completed by Marmontel (1993) indicated that even a small increase in adult mortality increased the probability of extinction (4, 5). |
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