Category Archives: Freshwater Fisheries Research

“Ghost Bass” Caught at Lake Apopka

This nearly white 11-pound bass was shocked this spring on Lake Apopka during electrofishing surveys. Continuing efforts by many agencies, including FWC, are helping to bring this once great fishery back to life. Research monitoring efforts show that much of the south section of the lake has excellent habitat and produces good numbers and size of bass. Bass from highly productive and/or low visibility waters are normally lighter in color, giving this impressive bass its ghostly hue.

Summer Bass Tournament Live-Well Study

By Ted Lange

FWC’s Black Bass Management Plan (BBMP) committed FWC to work with stakeholder groups to mitigate negative public perceptions of club-level bass fishing tournaments.  Negative perceptions identified included bass mortality, crowding at boat ramps and poor boating and angling ethics by some tournament anglers. Stakeholders also expressed positive perceptions of bass tournaments through the BBMP including promotion of fishing as well as teaching ethics and stewardship. Regardless, bass tournaments can be very high profile with potentially hundreds of club tournaments occurring in Florida waters each week throughout the year. FWRI biologists working with Division of Freshwater Fisheries staff are working to better understand and mitigate bass mortality caused by bass fishing tournaments through several projects.

The Summer Bass Tournament Live-Well Study was initiated to assess live-well water quality conditions during summer tournaments when bass are most susceptible to mortality due to warmer water which holds the least amount of oxygen. Study objectives are to 1) educate bass tournament anglers about live-well water quality conditions during summer tournaments, and 2) further refine FWC’s fish care guidelines for best live-well management practices under conditions specific to Florida.

Bass are weighed in.

During year one of a three summer study, FWRI biologists assessed water quality conditions at club-level tournaments (10-30 participating boats) based on anglers preferred practices. In year two, biologists prescribed specific live-well management practices to random tournament boats and evaluated the resultant water quality conditions. In year three, biologists ran controlled experiments with wild caught fish acclimated to hatchery conditions under three varying management practices. Through controlled experiments, blood stress parameters in bass exposed to these management practices were measured, and a post tournament mortality assessment was conducted.

Year one results, focused primarily on temperature and dissolved oxygen (DO), confirmed that competitive anglers manage their live-wells in a variety of ways resulting in a wide range of water quality conditions.  During year two, anglers were assigned specific live-well management regimes which included flow through only (near constant exchange of live-well water), fill and recirculate only (no exchange of water once filled), and fill and recirculate with one exchange of water midday along with the use of salt and ice. Year two results, more intensive and including more water quality parameters, suggested that anglers were reasonably able to maintain adequate levels of DO while minimizing the buildup of ammonia and carbon dioxide in live-well water.  During the summer months, when lake surface temperature can exceed 30 °C, it is critical that those holding fish in captivity to manage live-wells conditions to maintain or even stimulate the recovery of bass during the period of confinement.

FWC staff takes a blood sample from a bass.

During year three, biologists repeated year two studies with wild-caught bass held in the research tanks at the Florida Bass Conservation Center where they underwent a simulated angling event prior to being placed in controlled condition live-wells representing the three management regimes. Stress parameters of glucose, lactate, cortisol, chloride, and osmolality in blood plasma were sampled both pre and post live-well confinement to assess the effects of the live-well environment on bass physiology.  Finally, all bass were assessed for a seven-day period for post tournament mortality.

Blood samples are currently being analyzed by the University of Florida Veterinary Lab and the Ruskin Tropical Aquaculture Laboratory, UF IFAS.  Study results will be utilized in coordination with other study components investigating tournament mortality to update FWC fish care guidelines to provide Florida bass anglers with live-well best management practices that they can readily implement during summer months.

Assessing the Effects of the East Lake Tohopekaliga Littoral Habitat Restoration on Shallow Water Fish Communities

By Chris Anderson

East Lake Tohopekaliga (ELT) is a 4843-ha mesotrophic lake located in the Kissimmee Chain of Lakes in Osceola County. In the 1960s, water control structures and canals were constructed in the Kissimmee Chain for flood control. These structures stabilized water levels in ELT and the other lakes in the chain, reducing the magnitude of seasonal water level fluctuations. The water level stabilization eventually led to increased accumulation of organic material and excessive growth of invasive aquatic plants that contributed to an accelerated rate of lake succession in ELT. The vast monocultures of invasive aquatic vegetation (e.g., torpedograss Panicum repens and cattails Typha sp.) growing within the littoral zone created and trapped additional organic material and ultimately resulted in the formation and expansion of floating tussocks. Extremely dense vegetation and tussocks resulted in degraded fish and wildlife habitat and limited recreational access for homeowners, anglers and boaters.

Map of East Lake Tohopekaliga, St. Cloud, Florida, depicting the three treatment areas that will be restored and two unrestored control areas.

A lake drawdown and subsequent habitat restoration is set to begin on October 1, 2019. It will be a collaborative effort by FWC’s Aquatic Habitat Restoration/Enhancement subsection (habitat restoration), the South Florida Water Management District (water level regulation schedule changes), and the United States Army Corps of Engineers (overseeing drawdown). Once ELT has been dewatered, FWC biologists will utilize a combination of herbicide treatments and prescribed burning as well as mechanical removal of woody vegetation, tussocks and organic sediment to restore the littoral zone habitat (Figure 1). Herbicide treatments and prescribed burning will be used to control/remove monotypic stands of invasive vegetation (e.g., torpedograss and cattails) along the northern and western shores. Mechanical removal of woody vegetation (e.g., willows Salix sp. and water primrose Ludwigia spp.), tussocks and organic sediments will be completed along the eastern shore. Two areas along the southern shore will not receive any treatment and will be considered control areas. Once the habitat restoration is complete, ELT will be refilled via precipitation during the summer of 2020.

Fish captured in a mini-fyke net.

To evaluate the effects of the restoration, fisheries biologists are assessing potential changes in fish community composition, water quality, and habitat structure/composition in shallow (< 2 feet deep) littoral habitats pre- and post-restoration.  Researchers are deploying mini-fyke nets (MFNs) and dissolved oxygen (DO) logging sondes to sample the fish communities and DO regimes, respectively, in each treatment/control area (18 sites per area, 90 sites per year). Qualitative assessments of aquatic vegetation and quantitative assessments of organic sediment depth are also completed at each sampling site. Pre-restoration sampling will continue until the restoration begins in 2019 and post-restoration sampling will be conducted for at least two years after ELT has refilled.

Mini-fyke net and dissolved oxygen logger deployed in monotypic stand of torpedograss.

In 2016, the first year of pre-restoration sampling, a total of 4,847 fish comprising 26 species were captured across all successfully sampled sites (n = 88). Habitat data from 2016 indicated that the eastern shore (Mechanical Removal and Scraping area; Figure 1) had significantly deeper organic sediments and significantly lower aquatic plant density than the other four treatment/control areas of ELT. The second year of pre-restoration sampling was scheduled for 2017 but was cancelled because precipitation from Hurricane Irma resulted in water levels that were too high to effectively sample the littoral zone. Results from this study will help researchers and managers understand how habitat restorations influence shallow water fish communities, water quality, and habitat structure/composition. Understanding the effects that different restoration actions have on those parameters will provide managers with an idea of how future restorative efforts may influence the ecology of littoral habitats in lakes.

Bar Hopping: Searching for Imperiled Species in the Escambia River

By Kayla Smith and Chelsea Myles-McBurney

Our freshwater fisheries biologists in the panhandle are working on an imperiled species trawl survey in the Escambia River. Crystal darter (Crystallaria asprella), Gulf sturgeon (Acipenser oxyrinchus desotoi), saddleback darter (Percina vigil), pallid chub (Macrhybopsis sp. cf aestavalis), southern logperch (Percina austroperca) and river redhorse (Moxostoma carinatum) are listed as species of greatest conservation need, and are not routinely sampled during long-term fish monitoring surveys. These species share an important aspect of their life history: the use of gravel substrate is required at some point in their lifetime, making them gravel obligate species.

A crystal darter, freshly plucked from the Escambia River.

Prior to this project, only 11 crystal darters have been collected on the Escambia River since the 1970s. Crystal darters are known only to occur in the northern-most reaches of the Escambia River and little information exists on their distribution and habitat use. Using a mini-Missouri trawl, crystal darters and the other species mentioned above were targeted over gravel and sand bars. Since 2016, 357 trawls were conducted successfully. A total of 37 species were collected including five of the target species for the project. Although crystal darters are relatively rare, a total of 29 were collected during two years of sampling. These 29 individuals were all tagged using visual implant elastomer to determine if recapture was occurring.

Trawling was conducted both during the day and at night; however, researchers found that night trawling was much more successful at capturing crystal darters. In addition to the increase in crystal darters, researchers also captured a river redhorse, which had not been documented in the Escambia River since 1976. This individual was implanted with an acoustic tag and released. The movement of this fish will be monitored using Vemco VR-2 receivers to estimate site occupancy and assess population trend.

Apple Snails and Snail Kites

By Jenn Bernatis, Ph.D.

Changes in Florida’s freshwater ecosystems over the decades have had a myriad of impacts on native species. Now, we are looking at the possibility of relying on an invasive snail, Pomacea maculata, to support the federally listed Snail Kite (Rostrhamus sociabilis plumbeus). Snail Kites feed almost exclusively on Apple Snails, but population declines in the native Florida Apple Snail (Pomacea paludosa) appear to be occurring in traditional kite nesting areas. Over the last 12 years, the invasive P. maculata (Island Apple Snail) has spread throughout the state becoming an alternate food source in many systems where Snail Kites nest. Many of these nesting sites are manipulated for a variety of reasons, yet definitive impacts on the snails and birds remains uncertain.

East Lake Tohopekaliga is a nesting site for Snail Kites and home to both the Florida Apple Snail and Island Apple Snail. The lake is slated for an extensive restoration including draw-down, scraping and removal of sediment, and vegetation treatments. This system has provided state and federal researchers with the opportunity to monitor both snail and bird activity pre-restoration, during restoration, and post-restoration. The data collected during this period will provide much-needed data that can be used in determining future restoration activities at sites with Apple Snails.

At this time four sampling events, two summer and two winter, have been conducted. These sampling events use a combination of throw traps, transects, wading, snorkeling, and scuba diving to locate snails. More than 800 sites have been sampled around the lake ranging from 0.25 m to 2.25 m deep. More than half of the snails collected have been in depths greater than 0.75 m. The majority of the sites with snails have some sort of vegetation, either emergent or submersed, but a few snails have been collected at sites with no vegetation. More snails have been collected in the summer, as this is also peak reproductive period than in the winter. This finding demonstrates conclusively that snails utilize deeper water and that Apple Snail surveys need to focus on a range of depths and not just the shallow marsh areas.

Tracking the snails long term will provide information critical to dealing with Apple Snail populations. Although invasive Apple Snails are economically and potentially ecologically damaging, they are serving a critical role as a food source for the Snail Kite. Understanding the movement patterns and use of the water column by Apple Snails will allow managers to better anticipate the impacts on Snail Kites and adjust management plans accordingly. Likewise, the research will provide information that may be of use in developing snail eradication programs. Previous tactics have included draw-downs in an attempt to kill the snails through desiccation. This is not an applicable approach as it is known that invasive Apple Snails can survive out of the water for at least a year. The question that will be answered is, “Are the snails burying?” which they are capable of, or “Are the snails following the water?” at which point the draw-down will have minimal impacts on Apple Snails. If the snails bury, and scraping is part of the proposed activity, then reintroducing the Apple Snails, preferably the native, may need to be considered in locations with Snail Kite nesting history. Ultimately, this study will fill in missing data gaps on snail ecology and provide necessary information when working with systems with Apple Snails and particularly those with Snail Kites.

Post-Hurricane Impacts on the Middle St. Johns River

By Earl Lundy

Hurricane Irma had a definite impact on Florida, with over 2/3 of its counties feeling some of its effects. Biologists from the DeLeon Springs Freshwater Fisheries Lab have been monitoring conditions on the lakes and selected stretches of the middle St. Johns River since the storm subsided.

To start with, U.S. Geological Society (USGS) gages recorded river levels rose 3 to 6 ½ feet above normal water levels, depending on location. What was unique about Hurricane Irma was that it took so long for water levels to recede: three months out, water levels in some areas are still above their normal levels. While it took three months for waters to recede when hurricanes hit the state in 2004, that was with three hurricanes hitting the St. Johns River basin. Hurricane Irma was just one hurricane.

The high waters brought several issues. First, it flushed vegetation and debris out of area swamps and low-lying areas and set up a Biological Oxygen Demand (BOD) that contributed to lowered dissolved oxygen levels. Fish generally need a minimum of 2.0 mg/L of dissolved oxygen (DO) in the water, else a fish kill is imminent. FWC biologists, along with the Army Corps of Engineers, measured oxygen levels at several points along the St. Johns River and DO levels ranged between 0.09 and 1.5 mg/l due to the associated

impacts from Hurricane Irma. As was to be expected, dead fish of several species were observed. Recent community sampling activities have recorded dissolved oxygen levels more in line with historical levels, indicating that oxygen levels have rebounded.

Dead fish of various species at a St. Johns River boat ramp.

Further, runoff from terrestrial sources brought a lot of particulate matter into the river. This increased the turbidity and lowered light penetration, minimizing plant growth and oxygen production by submerged plants. Dark, tannin-stained waters that were flushed out of the local swamps also added to the shading effect and prolonged the time it took for regular oxygen production to resume. Secchi readings of lakes during community sampling have been one-half to one-third of historical levels. Discussions with local anglers indicated most of the fish caught have been higher up in the water column than they are normally found. While fish are being marked at deeper depths, it seems they are feeding higher, possibly due to an inability to see bait or lures.

Also, the winds Hurricane Irma brought caused A LOT of wave action, wave action that uprooted submerged and emergent plants. Biologists have observed large rafts uprooted plants in the lakes and river sections they are monitoring, mainly American Eelgrass Vallisneria americana, a native submerged freshwater tape-grass that provides valuable nursery habitat for sportfish, and refugia for various freshwater forage fishes. An additional stressor on what submerged aquatic vegetation is left will be the more turbid waters. High turbidity can prevent light from penetrating to submerged aquatic vegetation, causing the plants to cease photosynthesis and rely on dissolved oxygen in the water for respiration – dissolved oxygen that is initially at low levels after a storm. This can result in further loss of submerged aquatic vegetation due to oxygen deprivation. We’ve observed a loss of vegetation in most of the lakes we’ve surveyed so far, which was expected. We won’t begin to know the true extent of the loss of vegetation until water levels recede and the waters begin to clear. Further information will be gathered when the Long-Term Monitoring crew performs its vegetative surveys this summer. We’ll be able to compare the before and after surveys to better understand how much vegetation was lost. However, if past hurricanes are any indication, the lakes and river will bounce back, possibly taking a few years, but they will bounce back.

Trophy Bass Photo Analytics

By Drew Dutterer

TrophyCatch—FWC’s trophy bass conservation and citizen-science program—relies on photographic documentation of a bass’s weight for program qualification. Originally, the program required participants to photo document both weight and length of entrant bass to qualify for Lunker and Trophy levels and Hall of Fame level bass required on-site verification by a Florida Fish and Wildlife Conservation Commission (FWC) biologist. But due to concerns over excessive program participation guidelines, TrophyCatch has since transitioned to requiring only a single weight-documentation photograph for all three tiers of recognition. This simplification reduced handling of bass, reduced their time out of water, and made it easier for anglers to participate. However, by lifting the requirement of length-documentation photos, it left
TrophyCatch biologists with less information to help verify reported weights of entrant bass.

Example of photo documentation

This led FWC researchers to begin investigating alternative methods of verifying length and weight of trophy bass. Using photographs, they developed techniques now referred to as trophy bass photo analytics. In a nutshell, biologists use an object of known size in the photo (e.g., a standard 12-inch ruler) to scale dimensions within the focus of the photo, which can then be applied elsewhere in the shot. Similar to existing equations that use length and girth to estimate a bass’s weight, trophy bass photo analytics allows biologists to measure a bass’s length, body depth, or cross-sectional area in a photo, and these values can then be input into linear models that estimate weight.


TrophyCatch Photo Analytics

The trophy bass photo analytics models are informed by data from nearly 200 bass that were photographed, weighed, and measured in the field by biologists during 2014–2015. To make sure that these methods were applicable to bass of nearly all sizes, they included bass from 2.2–13.1 lbs; however, 65% of the bass were ≥ 8 lbs, since the project’s focus was to help verify weights of trophy bass.

Obviously, the accuracy of these techniques is largely dependent on the quality of the photo. The bass must be centered in the photo and perpendicular to the axis of the shot. If parts of the bass are angled toward or away from the camera they cannot be accurately scaled. As well, an object of know dimensions must also be centered and at the same focal depth in the photo as the bass. However, when all these conditions have been met, trophy bass photo analytics generates reasonably accurate estimates of bass size. For bass used in the study, our models estimated empirical total length to within ±30 mm for 85% of the observations, and we can estimate the weight to within ±500 g 79% of the time.

At this time, TrophyCatch submission approval team has incorporated trophy bass photo analytics as a tool in its submission validation process. If photo composition meets the criteria for the technique and if the validity of the submission is dubious, the process has been applied, and results have given the approval team greater confidence in approving or not approving some bass. In the future, the TrophyCatch team will be considering amending rules for photo documentation that ensure more submissions fit photo analytics criteria, especially for larger bass, which receive that greatest visibility and prizes.

Golden Shiners: We Don’t Know What We Don’t Know

By Scott Bisping and Andy Strickland

Golden shiners, Notemigonus crysoleucas, are one of the most popular, non-sportfish species in Florida and are greatly utilized among bass anglers throughout the state. Anglers trying to persuade the sometimes stubborn Florida bass to bite, often turn to golden shiners as the bait of choice. Of the 6,257 of submissions in the Florida TrophyCatch program (, 1,741 (28%) were caught on “natural bait” (primarily golden shiners). Golden shiners can be purchased at bait and tackle shops, where the price can range from $10-$26 per dozen depending on size and availability. Golden shiners at tackle shops are typically wild, and caught by commercial fisherman in public and private waters throughout the state. Harvest of wild shiners is largely unregulated, only requiring a commercial fishing license ($25) and a fish dealer’s license ($40) for commercial fisherman to harvest and sell golden shiners. There are no size or daily bag limits for commercial shiner fishermen, with no restriction on the size of cast net they can throw while fishing. In addition, recreational anglers who want to catch their own golden shiners to use as bait have no size or daily bag limit.

A typical monthly sample of golden shiners prior to otolith extraction.

Such liberal regulation of a species with considerable economic value raised concerns with researchers. Research biologists had no data with regards to age and growth of the species. Thus, researchers designed a project to determine if golden shiners could be accurately aged using otoliths, and attempted to validate annulus formation. Lake Jackson (Leon County) was the study lake selected for this project. Golden shiners were collected by boat electrofishing using a SmithRoot model GPP 7.5 with direct pulsed current at 120 pulses per second, 1,000 volts (@ 6-8 amps). Golden shiners were collected monthly over a 12-month period. All fish were collected within 5 days of the middle of each calendar month. We determined an individual total length (mm) for each fish collected in addition to collecting the lapillar otoliths. The lapillar otoliths were removed from each individual by cutting through the ventral side of the cranial region. Once removed, the otoliths were cleaned, air dried, and stored in glass vials until they were processed. An attempt was made to collect 1-3 dozen golden shiners each month and follow a specific cohort over a 12-month period to ensure that annulus formation occurred only once per year.

More than 400 golden shiners were sacrificed for the project in 2015-2016. A total of 180 golden shiners that were sacrificed represented the 2013 year class. We performed a marginal increment analysis for the 2013 cohort by calculating an index of completion (C) for each otolith where (C = Wn/Wn – 1, where Wn is the width of the marginal increment on the distal edge of the otolith and Wn – 1 is the width of the most recent complete increment. Otolith measurements were taken with a microscope eyepiece on a direct horizontal plane. The marginal increment analysis validated that golden shiners form one annulus per year. The index value (C) was highest from January through March and lowest in May and June, indicating that annuli were deposited during April and May. We recommend the use of lapillar otoliths for aging golden shiners to determine population characteristics including annual mortality, growth, and recruitment. This information could be used to better understand golden shiner populations and potential impacts from an unregulated fishery.

Trophy Bass Tagging Study

FWC biologists are busy collecting data on trophy-sized largemouth bass in Florida lakes. In addition to the data our scientists collect, much of what we learn about these large bass come from recreational anglers who participate in the TrophyCatch Florida Program. TrophyCatch serves as both an angler recognition program and a crowd-sourced data collection mechanism for trophy bass in Florida. Our new video highlights the work biologists and other stakeholders are doing to study and manage trophy bass in the state. 

Year-Round Use of Silver Glen Springs by Striped Bass and Hybrid Striped Bass

by Andrew Marbury

The St. Johns River (SJR) was historically home to the southern-most native population of Atlantic strain Striped Bass. However, natural reproduction of this stock was likely low compared to more northern rivers and was thought to have ceased completely by the 1970’s. Since the FWC and USFWS have stocked both Striped Bass (Morone saxatilis) and Hybrid Striped Bass (M. chrysops x M. saxatilis) into the system as a means of replacing this bygone fishery.

While these species are wide-ranging and can tolerate the mild water temperatures of winter, the Florida summer brings extremes that confine Morones to cool water refuges such as freshwater springs.

The view from above the 40-foot deep “chimney” at Silver Glen Springs. While few in number, Morones have been found to utilize this area in the winter as well as the summer.

Years of directed electrofishing and snorkeling surveys have led FWC biologists to believe that the “chimney” spring boil at Silver Glen Springs (SGS) holds one of the largest summer aggregations of Morones. In the past, researchers gauged the abundance and health of these fish through snorkel surveys at SGS from May to August, while utilization of the spring was at its highest. While not recorded, it was assumed that as temperatures in surrounding waters cooled in the fall, the fish would emigrate from SGS to the productive waters of the SJR.

To test this hypothesis, Morone residence has been recorded year-round at SGS since May 2016. Surveys involved snorkeling with underwater cameras in the summer months and the use of waders and an extendable “camera pole” throughout the winter. Typical summer aggregations (> 1,000) were present through October 2016 with fish health depreciating noticeably over this time, likely due to the lack of forage in the spring boil. By November 2016, numbers fell significantly to around 100 individuals but surprisingly, have remained at this level throughout the entire winter (through March 2017). Interestingly, fish health has improved over this time, suggesting some level of foraging.

An FWC biologist uses an underwater camera attached to a telescoping pole to get an abundance estimate of Morones at the “chimney” boil at Silver Glen Springs.


We will continue to monitor seasonal fluctuations of Morone abundance to determine when the majority of fish immigrate back to SGS. A telemetry study has been proposed for 2018 to determine both the temporal and spatial movements of Morones throughout the SGS and SJR systems. This should help to answer questions regarding residence time and foraging efforts while in thermal refuges, ultimately better informing managers on the feasibility of Morone stocking programs.