The green treefrog, with its bell-like, repeated “queenk-queenk-queenk” call, is abundant, and can be seen and heard easily during the breeding season, particularly at Royal Palm [Hammock] and on the Anhinga Trail.
The cold-blooded vertebrates, including fish, amphibians, and reptiles, play a significant role in the balance of life in the park, feeding upon each other and upon lesser animals and in turn being food for larger [predators] such as herons, hawks, raccoons, and otters.
Fishes
“Fishing Reserved for the Birds,” says the sign at the beginning of the Anhinga Trail. Actually, the catching of fish in the fresh waters of the park is an important activity not only for herons, anhingas, grebes, and ospreys, but also for raccoons, mink, turtles, alligators ... and bigger fish. Not surprisingly in the drowned [habitats] of [Everglades], even the smallest fish are important in the web of life.
One tiny species, the gambusia, is of special interest to us. This 2-inch fish is credited with helping keep down the numbers of mosquitoes by feeding upon their aquatic larvae. This accounts for its other name—mosquito fish—and for its popularity with humans. But its services to us are not the measure of the gambusia’s importance, for it is a link in many food chains in the park’s brackish and fresh-water [habitats]. Beginning with [algae], we can trace one such chain through mosquito larvae, sunfish, and bass, to end with the alligator. We can only guess at the extent of the [ecological] effects of the loss of a single species such as the little gambusia.
The larger fish of [Everglades] are the most sought after. Sport fishermen want to know where to find and how to recognize the many varieties of game fish, especially largemouth bass and such famed salt-water and brackish zone species as tarpon, snook, [mangrove] snapper, and barracuda. Because of its cycles of flood and drought, and the shifting brackish zones, however, the distribution and the numbers of fish fluctuate greatly in the glades and mangrove regions. At times of drought, the fish concentrations are particularly evident. In mid- or late winter, [sloughs] that are no longer deep enough to flow, pools, and other standing bodies of water will have a myriad of gambusia, killifish, and minnows. Larger fish seek the sanctuary of the headwaters of the Harney, Shark, and Broad Rivers. At such times concentrations of bass may be so great that the angler may catch his daily limit in a few hours. (There are no legal limits for the herons and ’gators!)
As water levels continue to fall, salt water intrudes farther inland; such species as snook and tarpon move up the now brackish rivers, and may be seen in the same waters as bluegills and largemouth bass.
In some years water levels drop so severely that concentrations of fish are too great for the [habitat] to support. As the surface water shrinks, the fish use up the available free oxygen and begin to die. The largest expire first; the smaller fish seem less vulnerable to depleted oxygen supply. Even though many tons of fish may perish in such a die-off, a few small specimens of each variety survive to restock the glades when the rains return.
With no cold season when fish must remain dormant, and with a year-round food supply, bass and sunfish grow rapidly and reach breeding size before the next drought.
These fish kills are associated with drought conditions that occur in the ordinary course of events, and thus are natural phenomena not to be considered [ecological] disasters. But man’s violent upsetting of the drainage patterns of south Florida, through airport, canal, and highway construction and other developments, can bring about such drastic shortages (or even surpluses) of water that irreparable damage could be done to the ecology of [Everglades] aquatic [communities].