DISCOVERING EVERGLADES PLANTS AND ANIMALS (continued)

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 of 10 fish 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.

While fish watching may not be the exciting sport that bird-watching is, you are the loser if you ignore this part of the life of Everglades. Fish are so abundant in the park that no one has to haul them in on a line to discover them. You can hardly miss spotting the larger fresh-water forms if you take the trouble to look down into the sloughs, ponds, and alligator holes.

Identifying the species of fish, however, is more difficult. The voracious-looking Florida spotted gar is an exception. This important predator on smaller fishes, which is in turn a major item in the diet of the alligator, is quite easily recognized. Experienced anglers will spot the largemouthed bass and the bluegill sunfish. You'll see these and others as you walk on the Anhinga Trail boardwalk.

As you watch alligators and other native Everglades predators, you may get an inkling of how important in the web of life are the prolific fish populations of the sloughs, marshes, swamps, and offshore waters of the park.