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Wetlands

, Volume 31, Issue 1, pp 147–155 | Cite as

Estimating Trends in Alligator Populations from Nightlight Survey Data

  • Ikuko Fujisaki
  • Frank J. Mazzotti
  • Robert M. Dorazio
  • Kenneth G. Rice
  • Michael Cherkiss
  • Brian Jeffery
Article

Abstract

Nightlight surveys are commonly used to evaluate status and trends of crocodilian populations, but imperfect detection caused by survey- and location-specific factors makes it difficult to draw population inferences accurately from uncorrected data. We used a two-stage hierarchical model comprising population abundance and detection probability to examine recent abundance trends of American alligators (Alligator mississippiensis) in subareas of Everglades wetlands in Florida using nightlight survey data. During 2001–2008, there were declining trends in abundance of small and/or medium sized animals in a majority of subareas, whereas abundance of large sized animals had either demonstrated an increased or unclear trend. For small and large sized class animals, estimated detection probability declined as water depth increased. Detection probability of small animals was much lower than for larger size classes. The declining trend of smaller alligators may reflect a natural population response to the fluctuating environment of Everglades wetlands under modified hydrology. It may have negative implications for the future of alligator populations in this region, particularly if habitat conditions do not favor recruitment of offspring in the near term. Our study provides a foundation to improve inferences made from nightlight surveys of other crocodilian populations.

Keywords

Alligator mississippiensis Crocodilian Everglades Detection probability Hierarchical model Monitoring 

Notes

Acknowledgments

This study was funded by the U.S. Army Corps of Engineers Comprehensive Everglades Restoration Plan Monitoring and Assessment Program, the U.S. Geological Survey Priority Ecosystems Sciences program, and the U.S. National Park Service Critical Ecosystem Science Initiative. We thank our many technicians for conducting nightlight surveys, two anonymous reviewers of the U.S. Geological Survey, Rebecca Harvey and Sara Williams for providing editorial assistance, and two anonymous reviewers for helping to clarify and contextualize the manuscript. Use of trade, product, or firm names does not imply endorsement by the U.S. Government.

Supplementary material

13157_2010_120_MOESM1_ESM.pdf (5 kb)
ESM 1 (PDF 4 kb)

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Copyright information

© US Government 2011

Authors and Affiliations

  • Ikuko Fujisaki
    • 1
  • Frank J. Mazzotti
    • 1
  • Robert M. Dorazio
    • 2
    • 3
  • Kenneth G. Rice
    • 3
  • Michael Cherkiss
    • 1
  • Brian Jeffery
    • 1
  1. 1.Ft. Lauderdale Research and Education CenterUniversity of FloridaDavieUSA
  2. 2.Department of StatisticsUniversity of FloridaGainesvilleUSA
  3. 3.U.S. Geological Survey, Southeast Ecological Science CenterGainesvilleUSA

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