Sampling Freshwater Fish Communities with Electrofishing

Biologists use electrofishing to monitor near-shore fish communities in Florida’s lakes.

Biologists with the Fish and Wildlife Research Institute (FWRI), as well as other FWC divisions, use a variety of methods to sample freshwater fish communities, depending on the target species, sampling location and habitat.

Electrofishing is a widely used sampling method that stuns fish for a short period of time. This technique allows researchers to handle specimens for data collection and return them safely to the water. As part of FWC’s long-term monitoring program, biologists use electrofishing to sample 25 different locations within a lake each fall. Every fish is identified, counted and measured. The types and numbers of fish they collect can answer a lot of questions about the fish community, for example:

• Is there enough prey for our big game fish to eat?
• Are there too many small fish and not enough big fish for our anglers to catch?
• Is the fish community evenly balanced, or is it made up of only a few species?
• Are there are any invasive species present and are they influencing the fish community?

Each year since 2006, FWC biologists have collected electrofishing samples from at least 30 lakes throughout the state. In that time, they logged 129 different fish species with an average of 25 species found in any given water body. Some of these species are observed every year. Biologists call these typical species. The most common of these species are two major sport fishes: bluegill and largemouth bass. They are collected in nearly every system, every year. Bluegill and largemouth bass, along with an important prey fish, threadfin shad, make up about 50 percent of the total fish collected.

Looking at this list of common fish species reveals several interesting facts about Florida’s fish communities.

Saltwater Species

Species like the Atlantic needlefish, common snook, hogchoker, and ladyfish, can be found in freshwater bodies that have a connection to the ocean. Some species, like the American eel, actually enter freshwater systems as part of their lifecycle. This species will grow and mature in freshwater, then migrate to oceanic waters to spawn.

Exotic Species

Some fish species are not native to Florida and only live here because humans transported them. Brown hoplo and suckermouth catfishes, which are commonly sold in the aquarium trade, often become established in Florida systems when owners release their pet fish in a local waterway. The most common non-native fish that biologists encounter is the blue tilapia, which is found in nearly 40 percent of lakes each year.

Dinosaurs

Among the typical species are several very old species. Gars and bowfin are living remnants of a prehistoric group of fishes that inhabited our waters over 100 million years ago. Both species have the ability to gulp air at the surface and get oxygen from their swim bladder, allowing them to live in very low oxygen conditions.

Florida’s freshwaters are full of interesting fishes that fill specific roles in our aquatic ecosystems, but their interactions with each other and their environments can be difficult to describe. Biologists at FWC use long-term monitoring data to learn more about these interactions and predict how future changes may impact these fish communities.