Fish kills are fairly common in South Florida. Most are caused by algal blooms or oxygen deficiency, but there are other causes, including excessively cold water temperatures resulting from the periodic invasion of unusually cold polar air masses. This was the case with a recent cold snap that saw daily minimum temperatures in much of South Florida plunge to freezing or near-freezing levels during a cold snap of unusual strength and duration. Cold water fish kills occurred on a widespread basis in the region. Biologists are now studying the impacts. One thing they already know is that the huge numbers of rotting fish are causing quite a stink!

If you’re going to be visiting Everglades National Park in the near future, and especially if you’ve made plans to fish or camp at Flamingo, you need to be aware of the abnormal situation that this recent prolonged cold snap produced in and near the park. Rotting fish carcasses are inflicting aesthetic insults on visitors in many areas of the park, and it will take a while for that to dissipate. Fishermen are also being affected by emergency changes in fishing regulations made necessary by the fish kills.

Cold water fish kills have significantly impacted marine species in all of the park’s western rivers and bays, in Whitewater Bay, and in all parts of Florida Bay. While some species, such as redfish and black drum, have apparently tolerated the cold without too much trouble, others have been very hard hit. Kill rates have been especially high for snook, tarpon, ladyfish, catfish, and smaller species such as pinfish and mojarra.

Since many campers, birders, boaters, fishermen, and other recreationists like to visit the park’s Flamingo area at this time of year (which offers cooler weather, fewer insect pests, and more birds), the fish kills there are particularly troublesome. The National Park Service has reported that

The Flamingo marina was the location of a concentrated fish kill; thousands of large dead snook, tarpon, and goliath grouper have been observed there. These fish are now floating throughout the basin and the smell of rotting fish will become more intense throughout the week. The dead fish will disperse with the tidal currents and continue to decompose. Over time, the basin's water quality and odor should return to normal.

Emergency measures adopted in the wake of the cold water fish kills apply to some of Florida’s most sought-after game fish.

The FWC recently extended the no harvest season for snook until September 1, 2010 and implemented a temporary prohibition on the harvest of bonefish and tarpon until March 31, 2010. Catch and release fishing is still allowed.

The Florida Fish and Wildlife Conservation Commission provides more details at this site.

Cold water impacts on the park’s freshwater fish may actually prove helpful, at least in the short run. That’s because fish native to Everglades waters fared lots better than the invasive species that don’t belong there.

Most of the impacts in the park’s freshwater wetlands were on non-native fish, such as the Mayan cichlid. The cold weather helps to control populations of these non-native fish, which have invaded many areas in the park.

Postscript: There’s yet another way that the recent cold temperatures have been helpful. The python hunters working to trim the park’s rapidly growing population of ecologically harmful constrictors find it easier to locate the snakes in cold weather. Snakes tend to remain hidden in warmer weather, but colder weather makes them seek out open areas (including road surfaces) where they can soak up sunshine.