Study Helping Water Managers Strike a Balance

Biologists help managers determine minimum flows and levels for freshwater bodies that serve the public's demand for freshwater resources, while safeguarding these aquatic habitats.
biologist observing habitat use of freshwater fish, caption belowA researcher observes the microhabitat use
of spotted sunfish, largemouth bass and
redeye chub.  When one of these fish is
seen, the observer measures water velocity and depth, and the type of cover and substrate (bottom) the fish is occupying.

Fresh water is a precious commodity, especially in Florida, where rain can be scarce for months at a time. Water is vital to people for a variety of reasons, but the state’s many lakes, rivers, creeks and other water bodies are also essential habitat for freshwater fish. The challenge for regulators is to manage the public’s demand for water while safeguarding this important habitat.

One way resource managers address this balance is to establish minimum flows and levels in water bodies to prevent significant harm to aquatic life. The Southwest Florida Water Management District has adopted 15 percent loss of habitat as the point at which they consider significant ecological harm is occurring. However, a peer review panel recommended taking a second look at that benchmark. As a result, the district designed a project to assess the effects of reduced water flows and levels on fish and wildlife.

In 2009, FWRI Freshwater Fisheries Research biologists were asked to collaborate on the project, which takes place at Gum Slough, a pristine, 4-mile long, spring-fed tributary of the Withlacoochee River in Sumter County. Researchers set out to determine the species composition of the fish community and the abundance and habitat preferences of largemouth bass, spotted sunfish and redeye chub under normal flow conditions. To establish which habitats these species prefer, snorkeling scientists search for fish in randomly selected locations and document where they first see each fish. They also record water depth and velocity, noting other habitat characteristics such as plants and woody debris.

Biologists compare these data with the same data from the rest of the slough. They then calculate an index of habitat suitability for the target species, which they use to predict the amount of habitat available as stream flow is reduced. To verify those predictions, researchers plan to monitor changes in abundance of the three species under various flow conditions by sampling fish twice a year at sites with both unaltered and manipulated flows. Biologists block off sample areas with nets and collect fish by electrofishing (a method that stuns the fish but causes no permanent harm). They then estimate the abundance of each species. 

Several more years of fish monitoring and flow experiments remain. The district will be able to refer to this project as it develops and implements minimum flows and levels to prevent unwanted loss of fish and aquatic habitats. As many water management regulations are designed to protect fish and aquatic habitats, the data gathered in this project could aid water management agencies throughout the state and beyond.

FWC Facts:
American eels spend 10 to 20 years in fresh or brackish waters only to migrate hundreds of miles to spawn in saltwater in the Atlantic’s Sargasso Sea.

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