Small Freshwater Fish Darting Out of Sight in Florida

Study on the southern tessellated darter will lay the groundwork for conservation of this species in North-Central Florida.

southern tessellated darter

A team of researchers have been trekking through the dense vegetation of the Ocklawaha River basin in North-Central Florida’s Marion and Putnam counties to search small streams for one of rarest freshwater fish species in the state. They were looking for the southern tessellated darter – a small freshwater fish that has been historically found at six locations in the basin. In recent years, however, this fish has only been consistently collected at one location. In 2010, experts with FWC, U.S. Geological Survey (USGS), and U.S. Fish and Wildlife Service recommended listing the southern tessellated darter as a state-listed threatened species because of its small known geographic range and low population numbers in Florida. This prompted the FWC to draft a conservation action plan to secure the Florida population to the point that these fish are present throughout their historic range. To achieve this, researchers must first learn more about darter population numbers, find out where these fish are located, and identify what habitats they prefer. In 2012, FWRI began a collaborative study with the USGS and the University of Florida to collect this information and lay the groundwork to carry out the plan.

To determine where these darters currently occur in Florida, researchers chose randomly-selected locations throughout the Ocklawaha River basin at sites where researchers could wade in the stream.  One researcher used a backpack electrofisher to apply a small electrical current to the water and stun the fish. Meanwhile, two other researchers stretched a seine net across the stream to collect all the fish that floated downstream.   After sampling 29 sites, the team ended up capturing 16 southern tessellated darters, all of which came from locations directly at or adjacent to locations within two streams where this species has been collected in recent years.  While researchers collected southern tessellated darters at new locations within the same two streams, the known range that these darters occupy in Florida has not expanded.

Scientists also obtained a tissue sample from each individual collected so they could analyze the genetic differences between fish in the same stream, those in different streams and those in the Florida population and populations from states further north.  Results indicate that the Florida population of southern tessellated darters is more similar to itself than it is to populations further north in Georgia, South Carolina, and North Carolina.  Researchers also found that the Florida darters have extremely low genetic diversity, suggesting that this population is low and has been low for a very long time.  Genetic results suggest that the Florida population has been isolated from the next closest population in Altamaha River, Georgia for approximately 150,000 years.  This information is important to managers who may consider supplementing the Florida population by introducing individuals into steams where they are currently known to occur and into other suitable streams.

In the summer of 2015, researchers returned to the two streams where they had success collecting the darters, in order to estimate a population size within those streams.  During this work, they sampled more than 1,100 meters of stream but only captured five individuals.  This extremely low capture rate makes it hard to estimate a population size and further suggests that Florida’s population of southern tessellated darter is very low.  Habitat protection within the areas where these darters are known to occur and other areas that may be suitable for the species to exist within Florida will likely be an important management strategy for the sustainability of this species in Florida.

More information on the project and a video showing sampling techniques and study sites can be found at: FWC's Southern Tessellated Darter Research

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