Cooperative manatee research in Puerto Rico.

The Antillean manatee (Trichechus manatus manatus) inhabits the coastal waters of eastern Mexico, and Central America, northern South America, and the Greater Antilles. Puerto Rico may be its only stronghold in the Greater Antilles. Significant numbers of manatees occur in Puerto Rico, with the largest concentrations along the southern and eastern coasts. Unlike in Florida, where manatees make extensive use of estuarine and freshwater habitats, manatees in Puerto Rico are found almost exclusively in marine habitats. As a result, manatees in Puerto Rico are entirely dependent on seagrasses for food.

Protected under the Endangered Species Act and the Marine Mammal Protection Act, manatees in Puerto Rico are under the jurisdiction of the United States. A recovery plan for manatees in Puerto Rico, prepared by the U.S. Fish and Wildlife Service, outlines tasks to identify and reduce human related mortality, identify and protect manatee habitat, and develop criteria and biological information needed for recovery of the Puerto Rico population. Population management and habitat protection measures specify the need for data from radio-tagged manatees on manatee movements and habitat utilization. Other specific tasks include determination of manatee food habits, mapping the distribution of seagrass beds and sources of fresh water, and establishing monitoring procedures for important habitat components. Habitat protection plans developed in Puerto Rico can serve as models for other Caribbean countries.

Scientists with the Sirenia Project at the U.S. Geological Survey's (USGS) Florida Integrated Science Center (FISC) are providing research findings to address the Service's manatee recovery efforts. Since 1992, the Sirenia Project and the Navy have cooperated on manatee research near Naval Station Roosevelt Roads in eastern Puerto Rico. The objectives of these studies have been to document manatee movements in Puerto Rico and assess the resources they depend on. This involves radio tracking manatees, mapping near-shore habitats with aerial imagery and ground verification, identifying seagrass beds, and studying manatee foraging strategies.

Radio-tracking Studies in Eastern Puerto Rico

Radio-tracking data from seven manatees tagged in the early 1990s revealed general movement patterns for manatees that used the waters off Naval Station Roosevelt Roads and Vieques Island, Puerto Rico. Satellite-determined locations and field observations identified areas where manatees feed, rest, and obtain fresh water. Several of these areas are important enough that the Navy has begun protecting them.

Mapping Benthic Habitats

As an extension of research on seagrass distribution and manatee use patterns, the Sirenia Project produced benthic (1) habitat maps in the 1990s for near-shore areas in eastern Puerto Rico and Vieques Island. This geographic information system (GIS) mapping effort used aerial photographs to delineate and map near-shore benthic habitats. The classification scheme included seagrasses, macroalgae (or "seaweeds"), hard bottom (coral reefs), mangroves, bare substrate, and dredged areas. Approximately 32 miles (51 kilometers) of shoreline were mapped at Naval Station Roosevelt Roads and 71 miles (114 km) at Vieques Island. The data were made available to the NOAA/NOS (2) Center for Coastal Monitoring and Assessment's Biogeography Program for production of a regional GIS assessment of benthic habitats of Puerto Rico and the Virgin Islands.

Seagrass Characterization Studies

Seagrass beds in eastern Puerto Rico, including those important to manatees, have been characterized and mapped in detail in order to analyze changes that occur over time or that follow specific disturbances. In collaboration with the NOAA/NOS Center for Coastal Fisheries and Habitat Research, detailed characterizations of these seagrass beds have established baseline parameters that can be used to assess the long-term ecological status of seagrass resources and associated animal communities. Detailed remapping documented changes to habitats caused by a major storm, Hurricane Georges, in 1998.

Changes for Manatee Habitats

After more than 60 years of naval activities in eastern Puerto Rico, over 8,000 acres (3,240 hectares) of the former Naval Station Roosevelt Roads are slated for transfer from Department of Defense to private and commonwealth ownership. Because the facility functioned as a naval port, training facility, and military quarters, security restrictions prevented non-military boating within the nearshore waters. As a result, much of the coastal area has been a de facto sanctuary for manatees.

With anticipated changes in land use following the end of Navy control, concern about possible impacts led the Service to request additional research on manatee activities. In coordination with Geo-Marine, Inc., the Sirenia Project began a project to identify habitat use patterns and specific resources used by manatees. With extensive seagrass beds available for forage but limited freshwater in the region, objectives included identifying freshwater sources used by manatees.

Ten manatees were tracked in May 2005 using global positioning system (GPS) tags that relay locations daily through a satellite link. They ranged over 30 miles (50 kin) along the coast from Cayo Santiago to Rio Fajardo, as well as along both coasts of Vieques Island. The GPS data revealed the location and frequency of use for sites where manatees access fresh water and forage, as well as their movements among these sites. The locations also show preferential use of areas within the harbor and coastal bays, especially in shallow, near-shore seagrass beds. To better understand these findings, the Sirenia Project continues to cooperate in studies with the Center for Coastal Fisheries and Habitat Research on seagrass beds and manatee feeding strategies. Other efforts include documenting hurricane impacts and seagrass recovery within disturbed sites. Similar research along Puerto Rico's southwest coast allows for comparative analysis with manatee tracking and seagrass studies along the east coast. This information will be provided to future land managers to maintain natural resources in the region.

These projects have been a cooperative effort of the U.S. Geological Survey, U.S. Navy, Service, Center for Coastal Fisheries and Habitat Research, GeoMarine, Inc., Puerto Rico Department of Natural and Environmental Resources, EcoElectrica, Florida Wildlife Research Institute, Caribbean Stranding Network, and dedicated collaborators and volunteers. With continued work, the manatee may before long come closer to recovery.

(1) (of, relating to, or happening on, the bottom of a body of water)

(2) National Ocean and Atmospheric Administration/National Ocean Service

Jim Reid is a biologist with the U.S. Geological Survey's Florida Integrated Science Center-Sirenia Project, based in Gainesville, Florida.