SOFIA - Poster - The Effects of Canals on Alligators in the Everglades (printable version)

The Effects of Canals on Alligators in the Everglades

Poster presented December 2000, at the Greater Everglades Ecosystem Restoration Conference

Matthew D. Chopp¹, Kenneth G. Rice², Frank J. Mazzotti³, H. Franklin Percival¹

Abstract

"Canal" alligator
Photo courtesy Julie Ehrstein
[larger image]

Drainage and diking projects in the Everglades have resulted in the creation of hundreds of kilometers of canals. In this research, we address the effects that canal habitats have on alligator (Alligator mississippiensis) population ecology. This project includes analyses of alligator hole characteristics, home range, habitat preference, population density and size structure, physical condition, thermoregulation, and production. This continuing research is being conducted throughout the Everglades including ARM Loxahatchee National Wildlife Refuge (LOX), Water Conservation Areas (WCA) 2 and 3, Big Cypress National Preserve (BICY), and Everglades National Park (ENP).

Introduction

"Marsh" alligator
photo: 1999 Tim Wiegmann
[larger image]

The alligator is a keystone species and an ecosystem engineer that physically influences the floral and faunal characteristics of the Everglades landscape. Information on Everglades alligator population dynamics is required to make management decisions concerning the importance of man-made and natural habitats to the species.

Restoration planning is currently underway for the Everglades under the Comprehensive Everglades Restoration Plan. A major unanswered question involves landscape decompartmentalization effects on wildlife populations. Our research demonstrates the effects of canal habitats on alligator populations. This information can be used directly to make restoration and management decisions, and indirectly through Across-Trophic Level System Simulation (ATLSS) model inputs and parameter estimates.

It has been accepted that the cumulative effects of annual flood and drought cycles in the altered Everglades system has negatively impacted alligator populations. The altered Everglades also contains hundreds of kilometers of canals. The extent to which canal presence has altered the habitats and reproductive parameters of the "keystone" alligator in this system is not fully understood (SFERT Science Subgroup 1997).

Objectives

In this research we address the effects that canal habitats have on alligator (Alligator mississippiensis) population ecology. Research objectives included understanding the following in canal and natural marsh habitats:

Alligator hole maintenance
Alligator home range and movement
Alligator production
Alligator habitat preference
Alligator physical condition
Alligator thermoregulation
Alligator population density and size structure

Alligator hole maintenance

Canal influence on alligator populations extends approximately 1 kilometer into the marsh (Mazzotti et al. 1999).

Alligator holes in Water Conservation Area 3A
[larger image]
Measuring an alligator hole in Shark Slough, Everglades National Park [larger image]

Distribution of observed and expected values of number of alligator holes in 1 km-wide transects [larger image]

Alligator home range and movement

Alligators living in canals use larger home ranges and move more than alligators in natural marsh habitats (See Home Range and Movement of Alligators in the Everglades, Morea et. al.).

Mean annual and seasonal homeranges for radio-tagged gators in WCA 3A North and ENP. [larger image]

Mean annual and seasonal minimum daily movement for radio-tagged gators in WCA 3A North and ENP. [larger image]

Alligator production

Alligator production and hatchling survival may be less in canal habitats (M. Chopp, Unpub. Data).

Marking alligator eggs in the nest
[larger image]

Alligator Nest Inundation Status

[larger image]
Alligator Nest Success

[larger image]

Year 2000 Preliminary Data taken at A.R.M. Loxahatchee N.W.R.

Alligator population density and size structure

Adult alligator densities are higher in canal habitats than those in the marsh interior (Mazzotti et. al., 1999).

Alligator Population Survey Routes
[larger image]

Average density of Alligators in Canals, Marshes and Rivers of the Everglades [larger image]

Alligator habitat preference

Habitat preference for canals among adults occurs, meaning alligators that live in canals stay there (See Home Range and Movement of Alligators in the Everglades, Morea et. al.).

Miami Canal, WCA
3A North [larger image]
Habitat availability and use for canal alligators located in WCA 3A North and ENP from 1 July 1997 to 21 September 1998. [larger image]

Alligator physical condition

Adult body condition may be better in canals than in the marsh.

Unhealthy/poor condition Everglades alligators in a legal Florida hunt [larger image]
Photo courtesy Florida Fish and Wildlife Conservation Commission

Healthy alligator in good physical condition [larger image]
Photo courtesy Adam Britton

Snout-Vent Length (SVL) vs. Mass

Body Length vs. Mass for alligators in the Everglades compared to other populations in northcentral Florida and South Carolina. [larger image]

Alligator thermoregulation

Canal alligators appear to have a metabolic thermal advantage in some seasons (See Thermoregulation of the American Alligator in the Everglades, Percival et. al.).

Technological advances have allowed miniaturization of temperature data logging devices so that continuous data collection is now possible through implantation.
Photo by M. Caudill [larger image]
The typical pattern of body temperature of an alligator
from WCA 3A North. [larger image]

Affiliations

1. U. S. Geological Survey, BRD Florida Cooperative Fish and Wildlife Research Unit 117 Newins-Ziegler Hall, University of Florida Gainesville, FL 32611
2. U.S. Geological Survey, BRD, FCSC Everglades National Park Field Station 40001 State Road 9336 Homestead, FL 33034
3. Department of Wildlife Ecology and Conservation Institute of Food and Agricultural Sciences University of Florida 3243 College Ave Davie, FL 33314

Acknowledgements

This research was supported in significant part by DOI's Critical Ecosystem Studies Initiative, a special funding initiative for Everglades restoration administered by the National Park Service; and in part by USGS's Florida Caribbean Science Center.

We would like to thank Mark Campbell, Adam Finger, Tori Foster, Phillip George, Stan Howarter, Corey Morea, Michelle Palmer, Travis Tuten, and Christa Zweig for technical and field work assistance.

Laura Brandt and Loxahatchee National Wildlife Refuge, Nat Frazer, Debra Hughes, Barbara Fesler, and Alan Woodward provided advice and logistical support.

Literature Cited

Mazzotti, F. J., L. A. Brandt, M. R. Campbell, and M. Palmer. 1999. An Ecological Characterization of Everglades Alligator Holes. Final Annual Report to Everglades Agricultural Area Environmental Protection District, NFW. UF-IFAS, Belle Glade, FL. 82 pp.

South Florida Ecosystem Restoration Taskforce, Science Subgroup. 1997. Ecologic and precursor success criteria for south Florida ecosystem restoration. A report to the working group of the South Florida Ecosystem Restoration Task Force, Chapter 12.

Related information:

SOFIA Project: Compilation of Alligator Data Sets in South Florida for Restoration Needs
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Alligator hole maintenance Canal influence on alligator populations extends approximately 1 kilometer into the marsh (Mazzotti et al. 1999).
Alligator holes in Water Conservation Area 3A [larger image]	Measuring an alligator hole in Shark Slough, Everglades National Park [larger image]
	Distribution of observed and expected values of number of alligator holes in 1 km-wide transects [larger image]

Alligator home range and movement Alligators living in canals use larger home ranges and move more than alligators in natural marsh habitats (See Home Range and Movement of Alligators in the Everglades, Morea et. al.).
Mean annual and seasonal homeranges for radio-tagged gators in WCA 3A North and ENP. [larger image]	Mean annual and seasonal minimum daily movement for radio-tagged gators in WCA 3A North and ENP. [larger image]

Alligator population density and size structure Adult alligator densities are higher in canal habitats than those in the marsh interior (Mazzotti et. al., 1999).
Alligator Population Survey Routes [larger image]	Average density of Alligators in Canals, Marshes and Rivers of the Everglades [larger image]

Alligator habitat preference Habitat preference for canals among adults occurs, meaning alligators that live in canals stay there (See Home Range and Movement of Alligators in the Everglades, Morea et. al.).
Miami Canal, WCA 3A North [larger image]	Habitat availability and use for canal alligators located in WCA 3A North and ENP from 1 July 1997 to 21 September 1998. [larger image]

Alligator physical condition Adult body condition may be better in canals than in the marsh.
Unhealthy/poor condition Everglades alligators in a legal Florida hunt [larger image] Photo courtesy Florida Fish and Wildlife Conservation Commission	Healthy alligator in good physical condition [larger image] Photo courtesy Adam Britton
Snout-Vent Length (SVL) vs. Mass Body Length vs. Mass for alligators in the Everglades compared to other populations in northcentral Florida and South Carolina. [larger image]

Alligator thermoregulation Canal alligators appear to have a metabolic thermal advantage in some seasons (See Thermoregulation of the American Alligator in the Everglades, Percival et. al.).
Technological advances have allowed miniaturization of temperature data logging devices so that continuous data collection is now possible through implantation. Photo by M. Caudill [larger image]	The typical pattern of body temperature of an alligator from WCA 3A North. [larger image]