U.S. Geological Survey scientists teamed up with government, nonprofit, and university partners in South Florida's Big Cypress National Preserve to hold a scientific scavenger hunt for nonnative and invasive freshwater fish species. 

Thirteen nonnative fish species were collected, including two not seen before on the Preserve: Nile tilapia and brown hoplo, also known as armored catfish. Last week’s Bio Blitz-like event, known as Fish Slam, marks the first nonnative fish survey in the Preserve in almost 15 years. Using canals and rivers like highways, nonnative fish in areas like the Everglades, Tampa Bay, and Naples may have an easy route into the Preserve, one of the most pristine parts of the region. 

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South Florida is well acquainted with nonnative and invasive species. Freshwater fishes like the Mayan cichlid and Oscar have become major problems in the region. Once a breeding population is established, nonnative fish species can reduce native fish populations by out-competing or preying on them.

“With conduits from the Everglades and the Tampa/Naples area, the Preserve could be a hot spot for nonnative and invasive fishes, but because it hadn’t been surveyed in more than a decade, we had no idea what kind of ‘biological pollution’ we would find,” said Pam Schofield, USGS research fish biologist. “Our goal for this Fish Slam was to figure out what species are out there. This information allows managers to be better-prepared to manage aquatic environments within the Preserve. It also gives us a more complete picture of the status of nonnative fishes across the state.”

Many of the nonnative fishes found in the Preserve may have been introduced by an accidental or intentional release, but it’s hard to really know, said Schofield. Nile tilapia, native to subtropical Africa, likely escaped from U.S. aquaculture facilities. Though sightings have been recorded throughout the state, it is not yet known if a population has been established in South Florida. Brown hoplo, however, have established populations throughout Florida, and may have been released into the canals as a food fish. Both Nile tilapia and brown hoplo compete with native fishes for food and space.

Fish experts from USGS, National Park Service, U.S. Fish and Wildlife Service, Florida Fish and Wildlife Conservation Commission, Audubon Florida, the University of Florida, and Florida International University split into eight teams to sample 28 water bodies within the Preserve, including culverts, canals, ponds, and ditches. The teams relied on a variety of techniques, including hook and line, cast nets, minnow traps, and electrofishing.

Data for all species collected will be submitted to the USGS Nonindigenous Aquatic Species database, which tracks sightings of nonnative aquatic plants and animals in the United States and is publicly available online. 

Fish Slam is the work of the Non-Native Fish Action Alliance, a group developed by USGS and FWC in 2013. The group consists of federal and state government agencies, universities, and nongovernmental organizations that work together to tackle the nonnative fish problem in Florida. USGS serves as the backbone of the alliance under Schofield’s leadership.

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“It is impossible for any one organization or agency to keep tabs on all nonnative fish species in Florida; every year we see new species and spreading populations,” said Schofield. According to Schofield, Fish Slam activities have grown each year, as has the sense of community and shared responsibility to take on the problem of nonnative fishes. 

What started as a small-scale, single-day fish survey in and around Loxahatchee National Wildlife Refuge is now an expansive effort directed at areas throughout South Florida. Fish Slam has grown to a two-day, twice a year affair, and the list of participating organizations grows with each event.  

“Participants pitch in to help survey for nonnative fishes, even when the event doesn’t take place within their jurisdiction” said Schofield.  “By working together and rotating sampling areas, we are able to provide a collective impact greater than any one group. A consequence of this work is that we have enjoyed improvements in communication among agencies, and that has led to better research coordination outside our Fish Slam activities.”

Fish Slams have previously targeted freshwater bodies in Miami-Dade and Broward counties, but the group decided to conduct their first-ever slam in the Preserve after a personal invitation from Preserve staff.

"Big Cypress is delighted to host our partners and cooperators for our first-ever Fish Slam,” said Tony Pernas, NPS biologist with the Preserve. “This effort helps us detect and survey our nonnative fish populations, an undertaking we could not tackle alone.” According to Pernas, visitors and fisherman can help the Preserve by reporting their catch or sightings on Florida's IveGot1 app and website. This data will help with the detection effort and inform management actions.  

The Fish Slam team will reconvene in Miami this November to continue nonnative fish sampling efforts.