 |  |
| Historic Drainage Patterns of South Florida | Current Drainage Patterns of South Florida |
Frank Mazzotti
Host Researcher: Herpetologist
Welcome to the crocodile habitat module. In this section we will look at how changes in the amount and location of freshwater flows into Florida Bay can influence the quality and location of suitable crocodile habitat.
By the end of this section you should be able to make recommendations to the U.S. Army Corps of Engineers and South Florida Water Management District on what water delivery patterns would maximize the amount of most suitable crocodile habitat.
BACKGROUND
The freshwater Everglades and estuarine Florida Bay are closely linked by patterns of fresh and saltwater movement. Impoundment of water upstream in the Water Conservation Areas and diversion of Water from Shark Slough and Taylor Sloughs for urban use and flood control have significantly reduced the volume of freshwater to Florida Bay.
| |
| Historic Drainage Patterns of South Florida | Current Drainage Patterns of South Florida |
As a result, Bay waters are now more saline in more locations and for longer periods of time than under premanaged conditions. Delivery of freshwater to Florida Bay today differs in timing and location of flows as well as reduced volume.
The dynamic storage (ability of the system to store wet season rainfall for continued release into the estuaries during the dry season) of the system has been eliminated by the need to provide flood control for agricultural and residential land uses north and east of Everglades National Park. Water that normally would have flowed down Taylor Slough is now directed in a more easterly direction through C-111. Numerous effects on biota have been observed including reduced recruitment of pink shrimp, snook and redfish lowered reproductive success of Ospreys and Great White Herons; shifts in distributions of manatees; and reduced growth and survival of crocodiles.
About one-half of the U.S. population of the federally endangered American crocodile live and nest in Florida Bay within Everglades National Park. Crocodiles live in an area likely to be influenced by changes in water flow patterns suggested as alternatives to restore the ecological health of the Bay. Because crocodiles are and endangered species, it is important to be able to predict and evaluate the effects of restoration on their continued survival.
THE MODELS
To evaluate the effects of different water flow patterns we used information on crocodile biology and salinities within Florida Bay to calculate the amounts and locations of suitable crocodile habitat.
Hatchling and juvenile crocodiles are the size classes most sensitive to changes in salinities. They grow and survive best in low salinities (< 10 ppt). They can not survive in water > 30 ppt for long periods without access to freshwater. Based on this information we have ranked areas of
In addition, the preferred habitats for small crocodiles are mangrove lined creeks, bays and ponds. So to locate suitable crocodile habitat we must use both criteria. To summarize, MOST SUITABLE crocodile habitat is areas of mangrove lined creeks, bays, or ponds with salinities < 10 ppt; INTERMEDIATELY SUITABLE habitat is areas of mangrove lined creeks, bays, or ponds with salinities 10-30ppt; LEAST SUITABLE habitat is areas of mangrove lined creeks, bays, or ponds with salinities > 30 ppt.
Now that we have established our model parameters, lets look at a year of salinity patterns in Florida Bay and the changes in amounts and quality of crocodile habitat.
DECEMBER 1993 End of Wet Season
This is the end of the wet season. 1993 was not an
exceptional year in terms of rainfall. Notice that the MOST
SUITABLE crocodile habitat is in the eastern portion of the Bay.
Look at Joe Bay, most of it is categorized as MOST SUITABLE
habitat. This is due to freshwater inputs into the Bay from
creeks along the northern shoreline. Joe Bay is one of the main
areas where we capture crocodiles.
What do you think will happen to the amount of MOST SUITABLE crocodile habitat in the Dry Season
Notice that even though it is the end of the wet season when most freshwater flow occurs into Florida Bay, not all of the area downstream of Taylor Slough is categorized as most or INTERMEDIATELY SUITABLE habitat. This is because water that historically might have flowed out through Taylor Slough is wither used in urban and agricultural areas or moved into canals and flows out C-111 so that residential and agricultural areas are not flooded.
What do you think would happen to the amount of suitable habitat if more water was allowed to flow down Taylor Slough?
APRIL 1994 End of Dry Season
Did you correctly predict what would happen to the amount and
location of suitable habitat? What has happened to the amount of
suitable habitat in Joe Bay? What effect do you think this has on
growth and survival of small crocodiles?
As you can see, there is less MOST SUITABLE crocodile habitat at the end of the dry season.
Amount of habitat (hectares) MOST INTERMEDIATELY LEAST SUITABLE SUITABLE SUITABLE Wet season 3435 6675 11110 Dry season 2036 8612 10562
The changes in salinities in Florida Bay are a result of changes in freshwater flows into the Bay. In the dry season there is less rainfall and more evaporation in south Florida both of which can cause increases in salinities throughout the Bay. Management of water north of the Bay has amplified these changes.
If you were a small crocodile, where would you want to be during the dry season? Continue reading to find out the answer.
HATCHLING CROCODILE HABITATS
July 1994 Wet Season
As it rains, more freshwater is available in all parts of
south Florida for human use and for flow into Florida Bay. As
more freshwater enters the Bay, salinities decrease resulting in
more and better crocodile habitat.
Notice how the distribution of suitable crocodile habitat has changed from the dry season. Most of Joe Bay is now classified as MOST SUITABLE habitat. Click here to see what happens to the amount and location of suitable habitat at the end of the wet season in a wet year or a "normal" year.
December 1994 End of Wet Season
1994 was a wet wet season. There was more freshwater
available for flow into Florida Bay both in the eastern portion of
the Bay near Joe Bay, and down Taylor Slough. The increase in
flow down Taylor Slough mimics what flows might have been under
predrainage conditions. As you can see, there is more MOST
SUITABLE and INTERMEDIATELY SUITABLE crocodile habitat.
Having evaluated the above scenarios you should now have an idea of what water delivery patterns would provide the greatest amount of the MOST SUITABLE habitat for crocodiles. Our conclusions from evaluation of the above models are:
1. More freshwater (lower salinity) in northeastern Florida Bay increases the amount and suitability of crocodile habitat.
2. Flows through Taylor Slough (rather than C-111) provide more and better crocodile habitat. 3. Under current conditions MOST SUITABLE crocodile habitat occurs closer to the C-111 drainage area than Taylor Slough.
Did you come to similar conclusions?
The following maps and graphs showing the drainage patterns of South Florida, the suitability of mangroves and coastal prairie as crocodile habitats and the length weight relationship for crocodiles are used in this activity:
JASON Project Homepage ||
Teachers' Guide ||
Students' Corner ||
Search
Gene Carl Feldman
(gene@seawifs.gsfc.nasa.gov)
(301) 286-9428
Todd Carlo Viola, JASON Foundation for Education (todd@jason.org)
Revised: 3 April 1996
