USGS - science for a changing world

South Florida Information Access (SOFIA)

projects > american alligator ecology and monitoring for CERP > project summary

Project Summary Sheet

U.S. Geological Survey, Greater Everglades Priority Ecosystems Science (GE PES) Initiative

Fiscal Year 2006 Study Summary Report

Project Title: American Alligator Ecology and Monitoring for CERP
Project Start Date: 2003 Project End Date: in 2007 will be companion study to CERP MAP
Web Sites:,
Location (Subregions, Counties, Park or Refuge): Total System
Funding Source: USGS GE PES, USACE CERP/MAP in 06
Principal Investigator(s): Kenneth G. Rice, Frank J. Mazzotti, H. Franklin Percival, Daniel Slone
Project Personnel: Chris Bugbee, Brian Jeffery, Wellington Guzman, Mike Rochford
Supporting Organizations: University of Florida

Associated / Linked Projects: MAP study: American Alligator Distribution, Size, and Hole Occupancy and American Crocodile Juvenile Growth & Survival, CESI study: Relative Distribution, Abundance, and Demographic Structure of the American Alligator in Relation to Habitat, Water Level, and Salinity.

Overview & Objective(s): Many important questions concerning the effects of Everglades restoration on alligator populations remain unanswered such as the impacts of decompartmentalization, the role of alligator holes as aquatic refugia, and the effects of hydrology on population growth and condition. Further, the methods for monitoring and evaluating restoration success are not clear or have not been adapted for use during CERP. Also, we need to continue to update and validate restoration tools such as population models for use in alternative selection, performance measure development, and prediction. This project will directly address the questions outlined above, develop monitoring methods, and validate restoration tools for use in CERP.

  • Develop monitoring methods necessary for evaluation of restoration success in alligator populations.
  • Understand the effects of decompartmentalization and other CERP projects on restoration of alligator populations.
  • Identify and quantify the extent of aquatic refugia maintained by alligators throughout the system and develop relationships necessary to predict restoration of refugia.
  • Validate and update ecological models for use in prediction of the effects of restoration.

Status: We are continuing to provide parameter information to the ATLSS alligator population model. We are adding to our information concerning the impacts of canals on alligator populations with investigations into alligator relative density, body condition, and size distribution. We have established monitoring of alligator population growth, condition, and size distribution throughout the Greater Everglades. We are investigating quantitative and field methods to improve the precision and accuracy of our monitoring through the use of double-observer surveys, artificial surrogates, radio telemetry, and mark recapture. We are currently mapping alligator holes and aquatic refugia within Everglades National Park. The ATLSS Alligator Production Index is now available for use in the restoration process but is also undergoing further calibration, validation, and updating with new data. The ATLSS Alligator Population Model has been completed and has undergone expert review, calibration, and some validation. Both models are fully functional and available for use in comparison of restoration alternatives.

Recent & Planned Products:

In FY06, 2 peer-reviewed journal articles, 1 proceedings paper, and 1 major technical report were published. We also gave several presentations at Local, National and International Conferences and 2 additional manuscripts were submitted to peer-reviewed journals.

Specific Relevance to Information Needs Identified in DOI's Science Plan in Support of Ecosystem Restoration, Preservation, and Protection in South Florida (DOI's Everglades Science Plan): [See Plan on SOFIA's Web site:]:

  • The role of alligator holes in providing dry season refugia was identified specifically as a science need for the Ten Mile Creek Reservoir - Assisted Stormwater Treatment Area Project (p. 35), the Water Preserve Area Projects (p. 45), and the Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement Project (p. 65, 69).
  • The study supports the L-31N Seepage Management Pilot and Everglades National Park Seepage Management Projects (p. 48) and Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement Project (p. 65, 69) by providing ecological monitoring and assessment of restoration impacts on the alligator.
  • Both models developed in this study (habitat suitability model and spatially explicit demographic model) are identified as Landscape-scale Science Needed to Support Multiple CERP Projects (p. 83).
  • The study supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structures project as it (1) provides monitoring and assessment of responses of aquatic communities and habitats (p. 37) and (2) helps understand the ecological effects of hydrology and water quality on refuge resources (p. 40).
  • The study support the Southwest Florida Feasibility Study Project by providing modeling to predict species-level responses to habitat change (p. 50) and monitoring of key indicators (p. 51).
  • The study provides improvement of ecological model to make them more suitable for application and analysis as identified in the Combined Structural and Operational Plan Project (p. 64).
  • Further, this study establishes the system-wide monitoring program for alligators as outlined in CESI- MAP.

Key Findings:

  1. We have been able to document the effects of canals and hydropattern on alligator production, movement, and body condition. This information has been incorporated into a population model that can be used for simulation of the effects of restoration including decompartmentalization.
  2. We have produced, calibrated, and validated 2 simulation models that can be used to compare the restoration alternatives throughout the Greater Everglades Ecosystem.
  3. We have developed a monitoring program for alligator populations that can be used to evaluate the effects of restoration throughout the Greater Everglades Ecosystem at differing time scales, including:
    1. Body condition (6 months-3 years);
    2. Abundance (3-5 years);
    3. Alligator hole abundance (5-7 years);
    4. Nesting (7-10 years).
  4. We have mapped alligator holes throughout the Everglades system for monitoring of alligator populations and use as the aquatic refugia data layer in other ecological models.
  5. System-wide, over 292 km of airboat trails and canals were surveyed for alligators in 2005. Count densities varied greatly from 0.3/km to 8.75/km.
  6. Our current survey program has sufficient power to detect a 5% decrease in the alligator population over 5 years.
  7. As we learn more about alligator populations in the Everglades, our monitoring program is becoming more efficient. As an example, power analyses show that additional surveys conducted in fall in canals are not effective and are no longer conducted.
  8. In general, total count densities were much lower in the Everglades than north-central Florida except for canals. While Everglades populations were probably never as dense as those in more eutrophic waters of north-central Florida, the densities in many current natural areas are certainly depressed.
  9. The largest difference between both north-central Florida and alligator populations in the Everglades is in the juvenile size class. Two causes of this difference have evidence:
    1. Nest flooding during certain years leading to reduced hatchling production.
    2. Decreased juvenile survival from predation and cannibalism during extreme dry periods.
  10. We were able to detect trends in alligator populations in several areas. However, in many cases these trends may not be biologically meaningful. Most trends were found on areas with only 2 or 3 years of data and therefore are probably temporary cycles in the counts and not changes in the actual alligator population.
  11. In Loxahatchee NWR, we were able to detect a 5 year increasing trend in the adult alligator population of only 3%. This demonstrates the ability of this program to detect even relatively small effects of hydrologic change.
  12. Improvements to alligator surveys include studies of alligator submergence and detection. These studies will decrease the amount of time required to detect trends during restoration.
  13. Our analysis of Everglades National Park's nest monitoring program demonstrates the influence of hydrology on alligators. This monitoring component will be a valuable indicator of restoration success.
  14. System-wide, we have captured approximately 1500 alligators for monitoring of alligator body condition. Condition was found to vary both temporally and spatially.
  15. We found decreasing short-term trends in body condition in several areas. The decreases could indicate temporary signals due to extended duration of high water levels from recent weather patterns including the hurricanes of 2004-2005.
  16. We have sufficient power to detect a 10% annual decline in body condition over 3 years on most areas.
  17. Alligator hole occupancy is proving to be an excellent indicator in areas inaccessible to ground-based monitoring.

| Disclaimer | Privacy Statement | Accessibility |

U.S. Department of the Interior, U.S. Geological Survey
This page is:
Comments and suggestions? Contact: Heather Henkel - Webmaster
Last updated: 04 September, 2013 @ 02:08 PM(KP)