Why are there skinny alligators? Establishing hematological and blood chemistry reference values for alligators in South Florida

Summary

Abstract: Alligators (Alligator mississippiensis) are both a keystone species and a flagship species that people care about. In Florida, alligators are ecologically, socially (tourism), and economically (alligator harvests and farming) important. The health of Florida’s alligator populations is of interest to FWC, FWS, and NPS as land and wildlife managers. In addition, the South Florida Ecosystem Restoration Task Force, South Florida Water Management District and U.S. Army Corps of Engineers are using alligators as indicators of ecological responses to Everglades restoration. Alligators are one species used to help plan restoration efforts because of their close ties to hydrologic conditions. We use alligator body condition as [...]

Summary

Abstract: Alligators (Alligator mississippiensis) are both a keystone species and a flagship species that people care about. In Florida, alligators are ecologically, socially (tourism), and economically (alligator harvests and farming) important. The health of Florida’s alligator populations is of interest to FWC, FWS, and NPS as land and wildlife managers. In addition, the South Florida Ecosystem Restoration Task Force, South Florida Water Management District and U.S. Army Corps of Engineers are using alligators as indicators of ecological responses to Everglades restoration. Alligators are one species used to help plan restoration efforts because of their close ties to hydrologic conditions. We use alligator body condition as a performance measure to track responses to ecosystem restoration. Body condition, defined by a mass-to-length relationship, is used to describe an animal’s health, quality, or vigor and how well an animal is coping with environmental stressors. Body condition also reflects energy reserves that can be used for growth or reproduction and can provide information about habitat quality. It is a non-destructive measure and data are relatively easy to collect.

Based on sampling conducted throughout the Everglades from 2004-2009 we used Fulton’s K, (K= [mass/snout vent length³] x 10⁵) and developed criteria to categorize alligators ≥ 1.25 m as in poor (< 1.96), fair (≥ 1.96-<2.10), good (≥2.10-2.27), and excellent(≥ 2.27) body condition. From 2000-2014 we documented an overall decline in average alligator body condition throughout the Everglades. Since 2015 six emaciated alligators have been observed on Florida Panther NWR in southwest Florida. In the last year, there have been reports of emaciated alligators in Fakahatchee Strand State Preserve, Ochopee, Everglades National Park (Anhinga Trail), Big Cypress National Preserve and Water Conservation Area 3 near the Miccosukee Indian Reservation. Although finding skinny alligators (Fulton’s K <1.96) is not unusual, what is unusual is the apparent increase in frequency and emaciated condition of animals (Fulton’s K < 1.50) in an area (Florida Panther NWR) where observations have not occurred in the past.
While we have good baseline data on alligator body condition in Everglades marshes in southeastern Florida, we do not have data on alligator body condition in southwestern Florida (Florida Panther NWR, Fakahatchee Strand State Park, Corkscrew Swamp Sanctuary) or complementary information in any area on blood chemistry and hormonal state which could provide an additional way to assess alligator health, and understand how alligators respond to current and future ecological conditions. For example, the ratio of heterophils to lymphocytes (H/L) may indicate differences in stress levels and overall health (Hanauska-Brown 2003). In addition, a recent study using blood samples of American crocodiles is showing the potential for using blood parameters such as CBC, glucose, triglycerides, uric acid, corticosterone and hydroxybuterate to track ecological responses and determine underlying causes of poor body condition. Blood parameters also may provide an earlier warning of unsuitable conditions than waiting until a significant portion of the population exhibits poor body condition. This would allow management action to improve ecological conditions sooner, before animals reach critical stress levels where they may be more susceptible to disease or can no longer recover from low body condition.

This project will:

Collect blood samples and body condition data on 60 alligators to help develop hematological and blood chemistry reference ranges for alligators in South Florida. This information will:
1. Assist in detecting effects of environmental and infectious stress on alligator health.
2. Help us to better understand physiological responses of alligators to changing environmental conditions.
3. Validate the use of body condition as an indicator of alligator health.
Conduct hematological and blood chemistry on up to five emaciated alligators. This information will:
1. Provide data on hematological and blood chemistry for alligators in extremely poor (emaciated) body condition.
2. Provide insights into potential causes of emaciated alligators.

Award ID: F17AC01071
Amount: $50,000
Start Date: September 18, 2017
End Date: December 30, 2020
Funding source: Science Applications Region 4
Recipient: Dr. Frank Mazzotti, Professor fjma@ufl.edu
Lead organization: University of Florida
FWS Point of Contact: Steve Henry (Project Officer), Deputy Project Leader Arthur R. Marshall Loxahatchee National Wildlife Refuge. Steven_s_henry@fws.gov. Science Applications contact Laura Brandt, laura_brandt@fws.gov.

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ALLIGA~1.PDF “Final Report for F17AC01071”		1.97 MB	application/pdf
FWS Alligator Health Final Report Deliverables.zip “All supporting data and files for cooperative agreement F17AC01071”		143.57 MB	application/zip

Related External Resources

Type: Citation

Hematology and Biochemistry Reference Intervals for American Alligator (Alligator mississippiensis) in South Florida, USA	https://bioone.org/journals/journal-of-wildlife-diseases/volume-58/issue-2/JWD-D-21-00142/Hematology-and-Biochemistry-Reference-Intervals-for-American-Alligator-Alligator-mississippiensis/10.7589/JWD-D-21-00142.full

Why are there skinny alligators? Establishing hematological and blood chemistry reference values for alligators in South Florida

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