Working Over Time

By Justin Hill

Long time no read. It’s been many moons since my last research blog. Rest assured, I have been working hard bringing the science to folks all over the Facebook-o-sphere and webiverse.

FWRI researcher measuring a largemouth bass collected during a routine electrofishing trip.

The Fish and Wildlife Research Institute’s Freshwater Fisheries Research section began a Long-Term Monitoring Project for Florida’s lakes in 2006. Our primary objective is to track freshwater fisheries trends over time, using standardized methods that ensure the integrity of the data collected across the state. This information can then be used to assess the overall health of Florida freshwater fisheries, direct research efforts and make management decisions. Each year, we collect data on the fish community, sport fisheries and aquatic habitat of more than 30 lakes and rivers. We add the information to a large database where it is available for use in future studies or evaluations conducted by us and fisheries managers. As of 2014, the database contains nearly one million fish data observations from 25,000 samples, and the number will continue to grow as the project expands.

Fish Collection Methods

A variety of methods are used to sample freshwater fish communities in the Long-Term Monitoring Project. The type of equipment used depends on the target species, sampling location and habitat. Here is a breakdown of the sampling gears we use and what we have found so far:

Electrofishing is used to collect fish in shallow water, 2-6 feet, during fall. Each year since 2006, we have collected electrofishing samples from at least 30 lakes throughout the state. In that time, we logged 119 different fish species with an average of 21 species found in any given water body. The types and numbers of fish we 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 any invasive species present and are they influencing the fish community?

The most common species observed are two major sport fishes: bluegill and largemouth bass. They are collected in nearly every system, every year. Along with an important prey fish, threadfin shad, these three species make up about 50 percent of the total fish collected.

Fyke nets are long, stationary nets with a lead extending to the lake’s edge designed to direct fish through two chambers and a funnel into a final collection chamber. Each summer, we sample approximately 10 to 15 Florida lakes with these nets and collect an average of 24 fish species. Many of these species are food for sport fish and indicators of the overall health of a freshwater system. To date, the most common fish collected were eastern mosquitofish and warmouth. Other common species included:

FWRI biologist retrieving a fyke net after a 24-hour sample.

• bluefin killifish
• bluegill
• brook silverside
• brown bullhead
• dollar sunfish
• Florida gar
• golden topminnow
• least killifish
• redear sunfish
• Seminole killifish
• swamp darter

Gill nets are tall stationary nets used to sample in deeper water where pelagic (open-water) species such as shads and black crappie are found. The nets are comprised of 25-foot panels of varying mesh sizes designed to collect fish of various sizes and body shapes. Gill nets were officially added to the project in 2009 and have been used in 26 lakes throughout the state.

Biologists recorded the following from 2008 to 2012 using gill-net sampling:

• Collected nearly 50,000 fish, representing 25 species.
• The smallest number of species (8) was collected in lakes Eloise (Polk County), Santa Fe (Alachua County) and Deer Point (Bay County).
• The largest number of species (20) was collected in Farm 13/Stick Marsh (Indian River County).
• Gizzard shad and threadfin shad were the most abundant species collected in the nets, accounting for approximately 80 percent of the total catch by number.
• Black crappie and bluegill were not as abundant as shad, but were observed in almost every lake sampled.

Currently, the use of gill nets has been suspended from the Long-Term Monitoring Project, in favor of the other sampling methods listed above. Following a recently published study using fish community data, researchers found that gill nets, for the amount of effort expended, collect fewer species than electrofishing and fyke nets. However, biologists will continue to use gill nets to target certain pelagic species, including channel catfish and striped. In addition, unlike the other gear types, gill nets are typically lethal, so other methods are preferred when the option is available.

FWRI researcher pulling in a floating gillnet.

Importance of Monitoring Data

Using the above methods, biologists monitor and measure the following:

• species diversity – an index of the number of species and abundance of each that make up a community
• species richness – a component of species diversity that represents the number of different species present in the community
• catch rate – an index used to estimate the relative abundance or density of fish, and can include values for all fish (total catch rate) or groups of fishes (e.g., catch rates of sport fishes or nonnative fishes)

The long-term monitoring project is another opportunity for scientists to research, monitor and record the history of the freshwater fish communities that are valuable resources to the state of Florida. State, federal and academic personnel use the data collected to develop management strategies and conduct related research as scientists produce a more complete picture of long-term trends.

A.D.D permitting, I have all sorts of new stuff headed your way. For some sneak peeks, remember to follow FWRI on Facebook at

No related items found.