Cooperative Manatee Research in Puerto Rico

Article excerpt


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. …