Category Archives: Freshwater Fisheries Research

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.

Small Lakes Stocking Study

By Nick Trippel and James Kramer      

A live prey-reared fish collected one year post-stocking during sampling on Lake Orienta

Biologists determined a need to do a head-to-head stocking comparison of live prey-reared vs. pellet-reared advanced fingerling Florida Bass Micropterus floridanus.  Eight small lakes (<100 ha) were selected for this study. In February of 2015, 45,791pellet-reared fish were microwire tagged in the right cheek. In May 2015, 42,102 live-reared fish were microwire tagged in the left cheek.  Both groups were stocked at a rate of 124 fish/ha. It was determined that the cost to raise fish was $0.38/fish for pellet-rearing and $0.30/fish for live prey-rearing.

James Kramer sampling Trout Lake one year post-stocking

Population estimates for stocked fish at one year ranged from 0 to 259 fish remaining for pellet-reared fish and 0 to 175 fish remaining for live prey-reared fish. Survival of live prey-reared bass ranged from 0% to 1.8%, and survival of pellet-reared bass ranged from 0% to 2.6%. The percent contribution of pellet-reared fish ranged from 0 to 16% and contribution off live prey-reared fish ranged from 0 to 41%. Combined numbers for both treatments of stocked fish to the total bass population ranged from 0% in Crystal Lake to 47% in Hardee Lake 4. These results are for one year post-stocking, but if similar for year two, when fish recruit to the fishery, it appears that survival is similar between the two treatments.  It also appears that lake selection to stock may be more important than rearing technique at the hatchery. Managers should focus stocking efforts on lakes with low adult abundance, low recruitment, and abundant forage.

New Species of Amphipod Discovered

By Mike Poniatowski

A new species of Amphipod was discovered in a sample as a part of the EPA’s National Coastal Condition assessment in 2015. Sediment was collected by FWRI researcher Dr. Paul Carlson and his team from the Wakulla River in northwestern Florida. Ten specimens (5 male and 5 female) were retained from the sample and examined by EcoAnalysts, Inc.

This new species, Hyalella wakulla, is most closely related to H. Azteca. One of the most abundant amphipod species in North America, H. azteca is the type species for a complex made up of cryptic species. H. wakulla is the first formally described species of Hyalella from Florida.

Assessing Temperature and Depth Selection of Trophy Bass: a Case Study at Kingsley Lake

by Drew Dutterer

In December 2015, FWC researchers launched a unique bass telemetry study at Kingsley Lake, in Clay County. Kingsley Lake stands out for two reasons — it is exceptionally deep for a Florida Lake (max depth 82’, ~300 acres ≥ 40’ deep), and it is home to an abundance of exceptionally large Florida Bass (Micropterus floridanus). Each year dozens of trophy bass, equal or greater than 8 lbs, have been reported from Kingsley to TrophyCatch, FWC’s citizen-science, trophy-bass conservation program. The lake has produced 14 of the program’s Hall-of-Fame bass(≥ 13 lbs), more than any other of Florida’s 7,700 waterbodies; and four of the top five heaviest bass documented by the program were from Kingsley.

A FWC researcher makes an incision to implant an acoustic telemetry transmitter into the body cavity of a Kingsley Lake bass.

The working hypothesis that attempts to explain Kingsley Lake’s unique bass population is the thermal stratification of the water column offers a cool-water refuge to bass during summer. Therefore, their metabolism is mediated, which could lead to faster growth, lower natural mortality or both. The researchers’ primary objective is to confront this hypothesis by implanting trophy bass with temperature- and depth-sensor acoustic transmitters and recording their spatial, depth, and temperature selection patterns for two years.

This bathymetric map of Kingsley Lake was generated from sonar recorded by FWC researchers at the start of this project. The contour lines show three-foot depth increments. The maximum depth is 82 feet, and most of the internal sub-basin is ≥40 feet deep.

Researchers implanted transmitters into 10 Kingsley Lake bass ranging in size from 9 to 13 pounds in December 2015 and January 2016. By combining frequent transmitter measurements (every 90 seconds), a lake-wide acoustic receiver array, and post-processed signal triangulation, the researchers will maintain near-continuous three-dimensional tracking of telemetered bass. Conditions throughout the water column available to bass will be recorded continuously through a series of temperature and dissolved oxygen loggers.

In the end, researchers will have extremely detailed data showing how members of Kingsley’s unusual bass population relate to their environment regarding temperature and depth. Ultimately, this study aims to reveal more information about how environmental factors influence bass growth, furthering our understanding of bass biology and bioenergetics.

Influence of Lake Productivity on Nearshore Fish Communities and Dissolved Oxygen Patterns

by Chris Anderson

net in water
A shallow, vegetated area in Lake Kerr (low productivity) where fisheries biologists deployed a mini-fyke net and dissolved oxygen logger to evaluate the influence of lake productivity on fish community composition and dissolved oxygen regimes.

During the summer of 2015, fisheries biologists deployed mini-fyke nets (MFNs) and dissolved oxygen (DO) loggers in four Florida lakes to assess the influence that lake productivity has on fish community composition, dissolved oxygen regimes, and habitat structure in shallow, vegetated areas of lakes. The four lakes evaluated were Lake Kerr (low productivity), Lake Dorr (medium productivity), Johns Lake (high productivity), and Lake Trafford (very high productivity). For each lake, the same 18 sites were evaluated during two sampling events to assess temporal variability of fish community composition and DO data collected at each site. The MFNs and DO loggers were deployed overnight, and the DO loggers were programmed to collect water temperature, DO, and conductivity data every 15 minutes. Additional environmental data was documented for each site including aquatic plant density and organic sediment depth. Once the MFNs were retrieved, biologists identified, counted, and measured all fish species collected.

people in lake with net
Biologists deploying mini-fyke net in a littoral zone site on Johns Lake.

Our results showed that fish community composition was similar between sampling events within lakes, but differed among lakes. Within lakes, duration of hypoxia (DO < 2 mg/L) did not differ between sampling events. However, higher productivity lakes (Johns and Trafford) had longer durations of hypoxia than lower productivity lakes (Kerr and Dorr). Differences in environmental data (e.g., aquatic plant density and organic sediment depth) were detected among lakes but rarely between sampling events within lakes. Understanding how lake productivity influences fish communities, DO regimes, and habitat in near-shore lake environments is important for effective aquatic resource management and policymaking.

Evaluating Florida’s Morone Stockings 
with Genetics 

by Ted Alfermann 

two men holding large fish
FWC fisheries biologists holding a 26 lb. female striped bass collected below Lake Talquin Dam
Picture credit: Ted Alfermann

Each spring, FWC researchers, managers, and hatchery personnel coordinate broodfish collection, spawning, and stocking of Morones (i.e., White Bass, Striped Bass, and their hybrids).  Fish are stocked in rivers and lakes from Pensacola to West Palm Beach, providing anglers the opportunity to catch some of the biggest and hardest fighting freshwater game fish in the state.  The success of the Morone stocking program is evident by the seasonally-popular fisheries they produce – but can we make it better?

FWC fisheries biologists currently have two research projects aimed at improving hatchery efficiency and making fishing better for the public: (1) determining hatchery contribution to White Bass year class strength in the Ochlockonee River above Lake Talquin, and (2) determining which stocking sites most contribute to the Striped Bass fishery and broodstock collections below Lake Talquin Dam.  Genetic information taken from fin clips of broodstock and fin clips from offspring in subsequent years will be used to determine results.  With hatchery pond space becoming more limited, biologists hope to better understand how often stockings are needed, where successful stockings occur, and what number of fish are required to produce quality fisheries.

Stocking will continue in 2016, covering nine rivers and 22 lakes across the state.  By offering anglers the chance to catch a diversity of game fish species and getting young anglers hooked on fishing with our hybrid bass stockings at Youth Conservation Center Network lakes, the Morone stocking program seeks to further the case that Florida is the Fishing Capital of the World now and in the future.