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3.4West Indian Manatee 3.4.1Description of the Species
The West Indian manatee includes two subspecies: the Antillean manatee (Trichechus manatus manatus) and the Florida manatee (Trichechus manatus latirostris). The Antillean manatee does not occur within the project area and is not considered within this consultation. The Florida manatee primarily occurs in two geographically distinct areas, one on the Atlantic coast and the other in the GOM, primarily along peninsular Florida.
The following information regarding manatees is summarized from the Florida Manatee Recovery Plan (USFWS 2001a and references within) unless otherwise stated. Florida manatees are massive (adults average about 10 feet in length and 2,200 pounds in weight), fusiform-shaped mammals with skin that is uniformly dark grey, wrinkled, sparsely haired, and rubber-like. Manatees possess paddle-like forelimbs, no hind limbs, and a spatulate, horizontally flattened tail. In the United States, manatees occur primarily in Florida during the winter. Manatees may range as far west as Texas on the Gulf Coast and on the Atlantic coast from Florida as far north as Massachusetts when water temperatures are warmer (USFWS 2007 and references within). On the Gulf Coast, manatees congregate mainly in central and south peninsular Florida; however, observations of manatees west of the Suwannee River during winter months have been increasing over the last decade (Fertl et al. 2005).
3.4.2Species Habitat and Distribution
In general, each spring as water temperatures increase, manatees disperse outside of their home ranges to waters along the Florida Panhandle, Alabama, Mississippi, and Louisiana (USFWS 2001a, Pabody et al. 2009, Fertl et al. 2005). In Alabama, a number of manatees (one to fifteen individuals) are routinely seen in the calm, shallow waters of rivers and sub-embayments of Mobile Bay and the Mobile-Tensaw Delta. However, manatees have been observed in the coastal areas, off barrier islands, and up to 90 miles (145 km) offshore (Pabody et al. 2009, Fertl et al. 2005). Manatees are often sighted in Alabama between mid-April through mid-October, though sightings of manatees have been reported in all months (Pabody et al. 2009). Manatees have been sighted in Mississippi and Louisiana typically in estuarine and river mouth habitats, though there have been sightings near barrier islands and offshore as well (Fertl et al. 2005). Based on data maintained by the Louisiana Natural Heritage Program (LNHP), over 80 percent of reported manatee sightings (1999-2011) in Louisiana have occurred from the months of June through December.
Cold weather and outbreaks of red tide may adversely affect these animals. However, human activity is the primary cause for declines in species number due to collisions with boats and barges, entrapment in flood control structures, poaching, habitat loss, and pollution (USFWS 2016b).
Manatees eat aquatic plants such as cordgrass, turtle grass and eelgrass and even non-native water hyacinth and hydrilla. They consume anywhere from four to nine percent of their body weight each day, which averages to about 32 pounds of plants a day. They spend about 5 to 8 hours eating each day. They can use their flippers to dig up plants and use their upper lip to manipulate leaves of plants for feeding. They also occasionally eat invertebrates and fish.
With no breeding season, manatees can mate at any time of the year. Females reach sexual maturity between three to ten years of age and will give birth to one or two calves young every 2-5 years. The calves nurse underwater from a nipple behind the mother’s forelimb. They can start eating plants right away, but will continue to stay with their mothers and nurse for up to two years.
3.4.3Status and Population Trends
The West Indian manatee (Trichechus manatus) was first listed as endangered in 1967 (32 FR 4061) under the Endangered Species Preservation Act of 1966. The listing was reclassified to threaten on May 5, 2017 (82 FR 16668). The USFWS has sole responsibility for entering into section 7 consultation for this species with other Federal agencies. In addition to the ESA, manatees are afforded protection under the Marine Mammal Protection Act (MMPA) of 1972, as amended (16 U.S.C. 1461 et seq.). The MMPA establishes, as national policy, maintenance of the health and stability of marine ecosystems, and whenever consistent with this primary objective, obtaining and maintaining optimum sustainable populations of marine mammals. It also establishes a moratorium on the taking of marine mammals, which includes harassing, hunting, capturing, killing, or attempting to harass, hunt, capture, or kill any marine mammal.
In the southeastern United States, the manatee population has grown, based on updated adult survival rate estimates and estimated growth rates (Runge et al. 2015). Historical and anecdotal accounts outside the southeastern United States suggest that manatees were once more common, leading scientists to hypothesize that significant declines have occurred (Lefebvre et al. 2001, UNEP 2010, Self-Sullivan and Mignucci-Giannoni 2012). Based on expert and local opinion, population trends are declining or unknown in 84 percent of the countries where manatees are found (UNEP 2010, Marsh et al. 2011, Self-Sullivan and Mignucci-Giannoni 2012). The magnitude of decline is difficult to assess, given the qualitative nature of these accounts.
The Florida Fish and Wildlife Commission (FWC) conducts a series of statewide aerial and ground surveys of warm-water sites known to be visited by manatees during cold-weather extremes to count numbers of manatees. These surveys are conducted from one to three times each winter, depending on weather conditions (FWC FWRI, 2016a). While the number of manatees has increased over the years, in and of themselves they are not considered to be reliable indicators of population trends, given concerns about detection probabilities. However, it is likely that a significant amount of the increase does reflect an actual increase in population size when this count is considered in the context of other positive demographic indicators, including the recently updated growth and survival rates (Runge et al. 2015).
In January 2010, FWC counted 5,077 manatees during a statewide survey prior to the start of the 2010 die-off. From 2010 through 2014, at least 2,822 manatees died. In February 2015, researchers counted 6,063 manatees during a statewide survey (FWC FWRI 2016b). These counts made before and after the die-offs, when considered in the context of positive demographic indicators (i.e., growth rates and adult survival rate estimates), suggest a certain resiliency in the Florida population (FWC FWRI 2016b, Runge et al. 2015).
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