Abstract

The issue of nonindigenous species is gaining increased attention at local, state, national, and global levels. There are many examples in Florida (and worldwide) where introduced plants and animals have caused ecological or economic harm or harm to human health, including crowding out native species (e.g., Brazilian pepper-tree Schinus terebinthifolius), economic damages to crops (e.g., Mediterranean fruit fly Ceratitis capitata), and human pathogens (e.g., West Nile virus Flavivirus). Consequently, concern over invasive species is justified (i.e., those introduced species that cause harm). However, only a subset of established nonindigenous species actually becomes invasive.

There are 32 reproducing exotic fish species in the State (i.e., fish moved by humans to the USA from another country) as well as a few species transplanted from other regions of the USA. The exotic species are primarily tropical in origin and are largely confined to the southern half of Peninsular Florida. In contrast, the transplanted species are temperate fishes and mostly occupy the Florida Panhandle. Cichlids (Cichlidae) are by far the most numerous group (18 species) with catfish species of various families (Siluriformes) the second most diverse group (at least 7 species). Introductions continue and several species are currently expanding in range. The major pathways of introduction of freshwater fishes into Florida are aquaculture escapes, aquarium releases, and legal and illegal releases for improvement of fisheries. A few species are fished commercially or recreationally in Florida and the butterfly peacock bass Cichla ocellaris is a regionally-important sport fish.

Given the large variety of nonindigenous fishes in Florida and the fact that they may reach high densities in some systems, there is a common perception that the effects of fish introductions in Florida have been catastrophic. Indeed, media coverage is frequently sensational and, unfortunately, often inaccurate. Furthermore, criticism can be extended to include the scientific literature and agency websites as well.

The main focus of research since the modern introductions began in the 1950s has been on species identity, geographic range, life history, and (occasionally) abundance of nonindigenous fishes. The effects of introductions are far less well documented. It is known that nonindigenous fishes in Florida dominate the biomass of some systems, consume native species, overlap with native species in resource use, aggressively defend breeding territories, alter habitat, and invade parks and preserves. Nevertheless, there are actually few data to suggest that introduced fishes in Florida, particularly in South Florida, have had large negative effects on native fishes at population or community levels.

Conceivably, nonindigenous fishes are having large negative effects yet there is a lack of data on these effects due to the scarcity of pre-introduction data, few or inadequate studies, or debate over the definition of effect. Alternately, the abiotic and biotic characteristics of Florida systems may interact with the characteristics of the introduced fishes such that native species typically do not decline following introductions. In Florida, documented negative effects generally occur at highly localized scales, with predation effects of introduced flathead catfish Pylodictis olivaris on a select group of species in Florida Panhandle rivers being the key exception. Perhaps surprisingly, given the usual perception of widespread harm, existing analyses (though few in number) suggest relatively little effect of nonindigenous fishes on Florida's native fish fauna.

Despite a relative lack of documented negative effects of freshwater fish introductions in Florida, nearly all introductions are illegal and undesirable. Although catastrophe has not occurred, nonindigenous fishes and their introduction pathways are important challenges to natural resource managers and regulators. In addition, nonindigenous species such as freshwater fishes support industries and recreational activities of high socio-economic value. Florida, with its long history of dealing with introductions, has a variety of regulatory, management, and educational responses.