Recent Fish Introductions into Southern Florida Freshwaters, with implications for
the Greater Everglades region
William F. Loftus and Leo G. Nico
U. S. Geological Survey, Florida Integrated Science Center, Miami and Gainesville, FL
Jeffrey Kline and Sue A. Perry
Everglades National Park, Homestead, FL
Joel C. Trexler
Florida International University, Miami, FL
Much has been published about introduced fishes in Florida, particularly their ability to
invade and potentially disrupt natural aquatic communities. Approximately 20 species
have been recorded as establishing populations in the extreme southern part of the state,
with many others having been collected without evidence of establishment. Recent
papers have examined data collected in southern Florida to evaluate the distribution and
relative abundance of introduced fishes across a variety of habitats. Two sampling
programs in the Everglades provided systematically collected density information over a
20-year period, and documented the first local appearance of four introduced fishes based
on their repeated absence in prior surveys. Freshwater canals, and natural tidal creeks
surrounded by mangrove-dominated wetlands, held the largest introduced-fish
populations in the southern Everglades region However, these combined studies
reported fewer species of introduced fishes from the Everglades region when compared
with studies conducted in canals along the developed Florida east coast, indicating that
the most likely sites of introduction for most species is in those canals. Recent
information on the appearance of additional species, and range expansions by established
fishes, demonstrates that colonization of the Everglades region is continuing. The eight
established species of introduced fishes known from the Everglades in the 1990s have
since been joined by additional species. What are these fishes, how were they
introduced, why are their ranges expanding, and what other species are likely to colonize
the Everglades?
The native inland fish community of the Everglades region is comprised by about 35
temperate species with wider distributions in Florida and the southeast US. Most
previously introduced fishes in the Everglades were tropical in origin, illegally released,
often from aquaria, and belonged to the family Cichlidae. One species each of livebearer
and clariid catfish also were
established there. Records indicate
that most of those introduced species
were released east of the Everglades
and used the canal system to move
into the Everglades system.
Although many became widespread
in the system, the majority did not
Pike killifish (Belonesox belizanus). L. G. Nico photo.
achieve great numbers except in
local situations. We hypothesize that a combination of cold winter temperatures and
unfavorable habitat structure may have limited success in natural habitats by some
previously established species.
Several widespread sampling
programs employing electrofishing,
trapping, and netting, and shorterterm research studies, continue to
provide information on introduced
species in the Everglades region.
Those studies, and ongoing
ichthyofaunal surveys of the Big
Pike Killifish (Photo: Leo Nico)
Cypress NP and Biscayne NP, are
continuing to collect data from
canals, marshes, swamps, and
detention areas. In recent years,
several new species have been collected either in the Everglades or in canals that border
the system. Although several are cichlids (jewelfish, banded severum, jaguar cichlid,
peacock bass), others belong to families not formerly found in this region (Asian swamp
eel-Homestead population, armored catfishes). In addition, other species are established
in the canal system to the east, from which dispersal towards the Everglades is likely
(Asian swamp eel – Miami population, snakehead, grass carp, various cichlids). While
some of these recent introductions are
probably aquarium releases, others
appear to be illegal introductions for
food or marketing purposes. Apart
from the accidental release of blue
tilapia from a Miami-Dade County
aquaculture facility, this class of foodfish planting by amateurs is a novel
vector for fish introduction.
Analysis of Everglades data collections
Asian Swamp Eel (L. G. Nico Photo)
found evidence for mainly local effects
by introduced fishes, but the long-term effects of introductions, particularly with the
continuing accumulation of species, are unclear. Experimental research into the biotic
interactions of introduced fishes and native species is needed, as is modeling research to
identify species that may pose problems if they were to be introduced. There should be
emphasis placed on additional monitoring of under-sampled habitats such as canals. We
also suggest that more efforts be made to educate the public about introduced species and
in closing newly identified pathways for the introduction of additional species identified
as potential threats.
Although there have been no dramatic ecosystem effects such as extinctions or largescale population declines in native species identified in southern Florida, we are uncertain
that this condition will continue under the cumulative effects of future invasions or
environmental change. What can be done to limit the numbers, spread and effects of
introduced fishes? At present, there are few options available to deal with introduced
fishes in the open habitats of southern Florida. Once a population has expanded beyond
its point of introduction into the main canal system or into the Everglades marsh, nothing
can be done to eliminate or even control them at this time. Control may be effective in
local situations to meet specific
management objectives. Even then, it
will have to be a sustained effort
because of the pool of recruits that
exists in the canal reservoirs. Unlike
the research and management funding
used to find and deliver controls for
plant or insect pests, there has been
little funding applied to research into
controls for fishes. Increased emphasis
on finding innovative methods for
dealing with fish invaders should be a
priority. At present, the best way to
prevent the continuing introduction of
fishes may be through better public education. We ask water managers and engineers to
think of the consequences when planning pump stations, detention areas, new canals, and
other constructs that will foster growth, dispersal, and delivery of non-native fishes,
snails, and plants into natural wetland areas. Just “getting the water right” is not enough
if it means the delivery of those waters will change the character of the Everglades biota.
William, Loftus, 40001 State Road 9336, Homestead, Florida, 33034,
Phone: 305-242-7835, Fax: 305-242-7836, Bill_Loftus@usgs.gov
•Heavy predation of small native species in drying pools, solution
holes, and canals
••Native fish nest predation and displacement