Radio Tracking Manatees to Assess the Impact of Hydrologic Changes in Southwest Florida

James P. Reid, Dean E. Easton, Lynn W. Lefebvre, and Susan M. Butler
U.S. Geological Survey, Florida Integrated Science Center, Sirenia Project

Poster presented at the16th Biennial Conference of the Estuarine Research Federation,
St. Petersburg Beach, November  4 - 8, 2001

ABSTRACT

The Sirenia Project is conducting a multi-year project to develop ecological models necessary to understand and predict the effects of hydrologic restoration on manatees (Trichechus manatus latirostris) in Southwest Florida.  As part of this effort, we initiated a radio tracking study in June 2000 to determine manatee movement patterns and habitat use prior to hydrologic alterations. We hypothesize that manatee distribution and movements will be influenced by changes in water flow patterns, particularly in the Ten Thousand Islands downstream from the Southern Golden Gate Estates and Faka Union Canal.

Fourteen manatees have been tracked within the Ten Thousand Islands/Everglades National Park region using satellite-monitored Argos tags from June 2000 through June 2001. Weekly movement patterns suggest a preference for foraging in marine areas with brief trips to inland creeks and canals, which provide sources of fresh water. During the winter months, one adult female migrated from the Pavilion Key/Chatham River area south to Whitewater Bay, where she spent several months before returning to her previous warm season range.  A data-logging GPS tag, which collects locational data at 15-minute intervals, was deployed on 3 manatees for two-week periods during 2000 and 2001. These data will allow us to determine fine-scale habitat use and provide accurate information on travel paths.

INTRODUCTION

As part of a multi-year project to develop ecological models necessary to understand and predict the effects of hydrological restoration on manatees in South Florida, the Sirenia Project initiated a radio tracking study to determine manatee movement patterns and habitat use. Given the reliance of this endangered aquatic mammal on freshwater and aquatic vegetation, we expect that altered water management regimes and resulting environmental changes may affect manatee habitat use and movement patterns.

The coastal waters of the Ten Thousand Island National Wildlife Refuge (TTI) and Everglades National Park (ENP) provide ample natural habitats for manatees. This is the first detailed radio tracking study of manatee use in the region.

METHODS

During the initial phase of this project, three manatees were tagged using satellite-monitored Argos tags.  These individuals were rescued in southwest Florida during the spring of 2000 because they exhibited symptoms of exposure to red tide. They were treated at Lowry Park Zoo and released during June 2000 in Rookery Bay, near Marco Island.

Manatee captures were conducted at Port of the Islands near Marco Island on 07-08 February 2001, and 20-21 March 2001. Eleven manatees were captured and radio-tag assemblies were attached to 9 of these (8 females, 1 male).

RESULTS and DISCUSSION
Click the graphics below to enlarge          

Tracking manatees with GPS tags

These data provide the first details on manatee use patterns in the TTI/ENP. Salinity of inshore waters fluctuate with winter dry periods and summer rains. Abundance and species composition of submerged vegetation within inland bays may vary with these seasonal changes, thus influencing manatee feeding patterns.

In this comparison of Argos and GPS data collected simultaneously from a tagged individual, precise travel paths, rates, and destinations can easily be identified.

CONCLUSIONS

Tracking data and field observations of tagged manatees reveal that the spatial distribution of submerged aquatic vegetation, availability of fresh water, and bathymetry influence manatee movements and use patterns within the Ten Thousand Islands.  Manatees routinely traveled from offshore seagrass beds to inland freshwater areas. We expect that altered water management regimes and resulting environmental changes may affect manatee habitat use and movement patterns within the Ten Thousand Islands. These data are being integrated into models that will attempt to predict manatee responses to these management actions.

The Sirenia Project at the Florida Integrated Science Center conducts long-term detailed studies on the life history, population dynamics, and ecological requirements on the endangered West Indian manatee (Trichechus manatus). This research provides managers with information that is essential to recovery assessment and planning.


ACKNOWLEDGMENTS

Manatee research is guided by the objectives of the Florida Manatee Recovery Plan. The studies summarized here are a cooperative effort with one or more federal, state, and private partners, including: Everglades National Park, U. S. Fish and Wildlife Service, Big Cypress National Preserve, Rookery Bay National Estuarine Research Reserve, Florida Fish and Wildlife Conservation Commission, Mote Marine Laboratory, and Save the Manatee Club.