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Spatial and Age-Structured Population Model of the American Crocodile for Comparisons of CERP Restoration Alternatives

Entry ID: USGS_SOFIA_pop_model_am-croc

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Summary

Abstract: To adequately understand crocodile populations and model population growth, existing data must be assembled and model parameters estimated. A simulation model can then be constructed and validated both with existing data and through expert opinion. A crocodile population model to simulate the south Florida ecosystem under varying management strategies is vital to evaluating and assessing ... restoration success under CERP. The objectives of this project are to: 1. Build an age and spatially structured crocodile population model suitable for comparison of CERP restoration alternatives. 2. Couple the local age-structured models into a spatial dispersal model incorporating crocodile movement behavior. 3. Use spatial parameter maps from the Florida Everglades as driving functions on the spatially structured model and to construct crocodile finite rate of increase maps under different management regimes. 4. Perform sensitivity analysis on the model parameters, and release model concept and code for peer-review.

The American crocodile (Crocodylus acutus) is a federally endangered top consumer in south Florida, imperiled primarily by habitat loss due to expansion of a rapidly growing human population along coastal areas of Palm Beach, Broward, Dade, and Monroe counties. This loss of habitat has principally affected the nesting range of crocodiles, restricting nesting to a small area of northeastern Florida Bay and northern Key Largo by the early 1970's. When crocodiles were listed as endangered in 1975, scant data were available for making informed management decisions. Field and laboratory data suggested that low nest success, combined with high hatchling mortality, provided a dim prognosis for survival. Because of their small size, hatchling crocodiles are vulnerable to biotic and abiotic stressors, such as high levels of salinity. To grow and survive, hatchling crocodiles need to find food and benign environmental conditions (or at least avoid harsh conditions) and avoid predators. Diminished growth rates and higher mortaity or dispersal rates have been associated with areas that pose greater risk to hatchling crocodiles. Crocodiles now occur in most of the habitat that remains for them in southern Florida. Most of the remaining habitat is currently protected in public ownership or engaged in energy production. In these areas, further loss of habitat is not an issue. However, questions of potential habitat modification through continued alteration of freshwater flow due to upstream development and potential curtailment of the range of crocodiles need to be addressed. Patterns of nesting, relative abundance and distribution, growth, and survival of crocodiles can provide insight into restoration of coastal ecosystems in Southeast Florida. For both Florida Bay and Biscayne Bay, restoring a more natural pattern of freshwater flow would provide the most benefit. Characteristics of flow patterns into Florida and Biscayne Bays that are beneficial for crocodiles include sheet flow through the fringing mangrove swamp that extends well into the dry season. Mid-to late dry season discharges of freshwater that cause a reversal of water levels in the receiving body are hypothesized to cause a dispersal of prey items, making them less available to crocodiles. If so, such discharges should be avoided. Shifting water delivery from Biscayne Bay to Florida Bay would degrade the quality of habitat in Biscayne Bay for crocodiles. Restoration efforts in the Comprehensive Everglades Restoration Plan (CERP) will likely cause changes to salinity levels throughout the habitat of the American crocodile. Changes in salinity were seen after previous hydrologic changes in the area, when reduced freshwater flow was associated with increased salinity levels in Florida Bay estuaries, including one of the core nesting areas of the American crocodile. Large crocodiles are not significantly affected by high salinity, but previous work has shown that high salinity levels may reduce survival of hatchlings and juveniles. The detrimental effects of high salinity on hatchling and juvenile crocodiles has led to the hypothesis that increased freshwater flow to the estuaries will increase the animals' distribution, abundance, and growth.

Related URL

Link: VIEW EXTENDED METADATA

Link: VIEW PROJECT HOME PAGE

Geographic Coverage

(Click for Interactive Map)

Spatial coordinates

N: 25.75

S: 25.7

E: -80.5

W: -81.25

Data Set Citation

Dataset Originator/Creator: Daniel H. Slone Kenneth G. Rice; Frank J. Mazzotti

Dataset Title: Spatial and Age-Structured Population Model of the American Crocodile for Comparisons of CERP Restoration Alternatives

Dataset Release Date: Unpublished Material

Online Resource: http://sofia.usgs.gov/projects/index.php?project_url=pop_model_croc

Temporal Coverage

Start Date: 2008-01-01

Stop Date: 2009-12-31

Location Keywords

CONTINENT > NORTH AMERICA > UNITED STATES OF AMERICA

CONTINENT > NORTH AMERICA > UNITED STATES OF AMERICA > FLORIDA

Science Keywords

BIOSPHERE > TERRESTRIAL ECOSYSTEMS > WETLANDS

BIOLOGICAL CLASSIFICATION > ANIMALS/VERTEBRATES > REPTILES > ALLIGATORS/CROCODILES
BIOSPHERE > AQUATIC ECOSYSTEMS > WETLANDS
BIOSPHERE > ECOLOGICAL DYNAMICS > SPECIES/POPULATION INTERACTIONS > POPULATION DYNAMICS

ISO Topic Category

BIOTA

ENVIRONMENT

Project

USGS_SOFIA > South Florida Information Access

Access Constraints None

Use Constraints None

Ancillary Keywords

Miami-Dade County

Collier County

Data Set Progress

IN WORK

Data Center

SOUTH FLORIDA INFORMATION ACCESS, FLORIDA INTEGRATED SCIENCE CENTER, U.S. GEOLOGICAL SURVEY, U.S. DEPARTMENT OF THE INTERIOR

Data Center URL: http://sofia.usgs.gov/

Data Center Personnel
Name: HEATHER S. HENKEL Phone: 727.803.8747 ext. 3028 Fax: 727.803.2032 Email: hhenkel at usgs.gov Contact Address: USGS-FISC-St. Petersburg 600 Fourth St. South City: St. Petersburg Province or State: FL Postal Code: 33701 Country: USA

Personnel

TIM GREEN

Role: TECHNICAL CONTACT

Phone: 352.264.3556

Fax: 352.374.8080

Email: tgreen at usgs.gov

Contact Address:

Crown Pointe 2201 NW 40th Terrace

City: Gainesville

Province or State: FL

Postal Code: 32605

Country: USA

ALICIA ALEMAN

Role: DIF AUTHOR

Email: alicia.m.aleman at nasa.gov

Contact Address:

Goddard Space Flight Center

Code 610.2

City: Greenbelt

Province or State: MD

Postal Code: 20771

Country: USA

Publications/References

Slone, D.H., Rice, K.G.; Allen, J.C., 2003, Model evaluates influence of Everglades restoration plan on alligator populations (Florida), Ecological Restoration, V. 21, n. 2, Madison, WI, University of Wisconsin Press.

Mazzotti, F.J., Cherkiss, M.S., 2003, Status and Conservation of the American Crocodile in Florida: Recovering an Endangered Species While Restoring an Endangered Ecosystem, Technical Report, Final report V. 1, Ft. Lauderdale, FL, University of Florida, Ft. Lauderdale Research and Education Center, Prepared for the National Park Service. http://crocdoc.ifas.ufl.edu/research/reports/american_croc2003.pdf

Creation and Review Dates

DIF Creation Date: 2008-11-03

Last DIF Revision Date: 2009-02-20

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