Category Archives: Freshwater Fisheries Research

Assessing temporal and spatial trends in fish assemblages within spring runs of the St Johns River basin

By Phillip Parsley

Springs in the middle St. Johns River basin are known for their clear water, intrinsic beauty and unique wildlife viewing opportunities.  Every year tourists and residents spend countless hours swimming in headspring pools or paddling down spring runs enjoying the breathtaking scenery of wild Florida.  However, recent natural events as well as anthropogenic influences have altered our perceptions regarding the health and vulnerability of some of these springs. Researchers and stakeholders have started to notice that lush aquatic vegetation has been replaced by dense algal mats and fish abundances have drastically reduced and been replaced by exotic fish species as habitat and water quality deteriorates.

While numerous studies exist that describe water quality of springs in the St. Johns River basin and include information on plant and invertebrate communities, information describing the fish communities of these springs is lacking.  In order to better understand the complexities of these fish assemblages, primary goals of this project were to determine an efficient sampling protocol for eight springs and their associated spring runs in the St. Johns River basin that will provide baseline data on community fish assemblages; and to document the presence of exotic fish species utilizing springs and how their abundances may change seasonally.

Figure 1. Locations of study springs within the St. John’s River Basin.

The springs and their associated runs in this study are Alexander Springs, Gemini Springs, Juniper Creek, Rock Springs, Salt Springs, Silver Glen Springs, Spring Garden (also known as DeLeon Springs), and Wekiva Springs (Figure 1). 

FWC standardized river sampling protocols were followed as closely as possible. However, some of the spring runs contained areas of dense aquatic macrophytes and a standard electrofisher boat was not practical.  An airboat electrofisher was used instead in these types of areas to avoid the unnecessary destruction of critical vegetation.  Also, a smaller boat we called the “mini-shocker” (Figure 2) was used in Rock Springs Run due to the narrow nature of the run and shallow areas where an electrofishing boat could not access.

A total of 406 sites spread across the eight study springs have been sampled since this project began in March 2019.  204 sites were sampled during the first round of sampling in summer 2019 collecting a total of 21,933 fish comprising 59 different species.  202 sites were sampled in winter 2019-20 and this netted 15,705 fish and 56 different species.  As one may expect, Bluegill (14.9% of total combined catch), Redbreast Sunfish (13.7%), Spotted Sunfish (12.6%), and Largemouth Bass (6.3%) were the most common sportfish encountered as far as total abundance.  Largemouth bass also comprised over one-fourth (25.3%) of the total percent biomass across all samples, with Bowfin (19.3%), Florida Gar (8.8%), and Lake Chubsuckers (8.7%) the next highest contributors.

Figure 2. “Mini-shocker” boat used to sample Rock Springs Run.

Five exotic fish species were collected during both rounds of sampling.  Blue Tilapia (n=153), Brown Hoplo (n=23), Dimerus Cichlid/Chanchita (n=4), Vermiculated Sailfin Catfish (n=62), and Walking Catfish (n=6) were all found to occur in multiple spring runs, however, they only represented 0.7% of the total catch and 4.3% of total biomass, both very miniscule portions of the entire sample.  Standard electrofishing procedures do not appear to be the best method for capturing an accurate representation of the numbers of exotic fish species occurring in the springs so in the future utilizing alternative methods could provide us with better information. 

The Bluenose Shiner (Figure 3), a state listed threatened species, was collected in Rock Springs Run and the Wekiva River.  Isolated populations of this species occur in the St. Johns River Basin and this fragmentation makes it vulnerable to extirpation from this region.  Finding this species in some of our study waterbodies was a positive and brainstorming is already underway as far as future research projects that could contribute to better understanding how best to conserve this species.

Figure 3. Bluenose shiner collected from Rock Springs Run.

Through days of field work over the past year we believe we have developed efficient sampling procedures for our study systems.  By using those protocols, we now have extensive sampling that yielded a total of 37,638 fish and 63 different species.  Calculating similarity indices between sample seasons will help us better analyze how these community assemblages may change in each spring as well.  Hopefully, the data collected in this study can provide future researchers insights and direction on the best way to make decisions regarding the health and viability of these springs as unique ecosystems. 

Understanding the Gravidity of the Situation: Developing a Calendar of Freshwater Mussel Reproduction

By Susan Geda and Lauren Patterson

Freshwater mussels within the family Unionidae are one of the most imperiled groups of animals in the world. Of the 61 species that occur in Florida, 60% are endemic to Florida river basins and over 25% are listed under the endangered species act. To aid freshwater mussel management efforts, the FWC Freshwater Mussel Conservation Program (FMCP) implements standardized sampling for the long-term monitoring of mussel populations statewide.

An important aspect of long-term monitoring is understanding reproductive requirements of target populations. Freshwater mussels possess an extremely unique life cycle, requiring a phase of parasitism during larval development that uses freshwater fish as hosts. Glochidia (larvae) are brooded in the female mussel’s gills, undergoing several developmental stages. Once mature, the mussel creates a shockingly accurate lure to mimic prey of host fish. When the fish bites, glochidia burst from the mussel and attach to the fish’s gills. Glochidia then transform into juveniles and drop off into the sediment, hitchhiking into new habitat. This process, as well as the migration of some fishes, is often mediated by water temperature. Therefore, as global temperatures rise, so does the probability that mussel and fish host distributions will not overlap during reproductively active intervals. When the timing of these natural phenomena no longer coincides with historical spawning seasons, species and the ecosystems that they support often fail to withstand the repercussions.

Collaborative efforts between FMCP and the U.S. Geological Survey resulted in publication of a non-lethal protocol for assessing gravidity (reproductive stage) in freshwater mussels. The protocol standardizes field and laboratory methods, a necessity considering previous studies classifying stages of larval development lack consistency. Uniformity of developmental stages allows results to be compared among all occurrences and species, enabling FWC biologists to develop the Freshwater Mussel Gravidity Almanac (FMGA), an online research tool for compiling and visualizing gravidity information collected using the published protocol. Being able to conceptualize when mussel species are brooding mature larvae throughout the year will help managers and biologists identify trends and data gaps, determine when to collect mussel broodstock, monitor impacts of climate change, and inform management decisions regarding fish and invertebrate populations. Thus, FMGA will facilitate future research, conservation and recovery efforts.

In the coming months, the FMCP will publish and integrate over ten thousand gravidity records collected since 2015. Conclusions drawn from the FMGA will become more robust as the dataset expands. Hence, this is where we ask for your help! Records of gravidity observation can be submitted through our desktop webpage or mobile application. Links for both can be found on the FMGA home page where the gravidity calendar and collection data are hosted. Once a submitted record and associated identification are validated, it is incorporated into the interactive gravidity calendar. The protocol includes visuals and character descriptions for differentiating each stage of development, and the phone application is user-friendly. Field surveys, long-term monitoring projects, and museum collections all present opportunities to contribute data and broaden the FMGA for a wider body of interest. Adoption of crowdsourcing projects like the FMGA will provide a more accurate understanding of population dynamics and further the conservation of these highly imperiled and extraordinary organisms.

Problems Equal Opportunities

By Ryan Henry and Andy Strickland

Hurricane Michael made landfall in the Florida Panhandle in October 2018. With sustained winds of 160 mph, Hurricane Michael was the strongest hurricane to hit the Florida Panhandle since record-keeping began in 1851. The east side of the eyewall swept up through the Chipola River drainage, resulting in the destruction of many small towns along the way. Heavy winds and rain destroyed much of the riparian zone, compromised sewage systems and flushed many, low-oxygen, swamp areas. Subsequently, several fish kills were reported on the Chipola River in the days following Hurricane Michael.

Young of the year shoal bass collected from the Chipola River.

The Chipola River is home to the only known population of naturally reproducing shoal bass (Micropterus cataractae) in Florida. They are listed as a species of greatest conservation need by the Florida Fish and Wildlife Conservation Commission and have historically been found in a 30-km stretch of the Chipola south of Marianna. Following Hurricane Michael, water levels remained high and unable to be sampled for nearly seven months. When water levels receded, a Shoal Bass abundance survey was conducted. This was the first sampling event targeting shoal bass on the Chipola River since fall 2017, when 361 individuals were collected. During four sampling events in May 2019, only 33 adult shoal bass were collected. This is a 91% decrease in catch compared to the most recent sample before the storm. Subsequent sampling in August and October also showed very low numbers of adults, though some reproduction for 2019 was documented.

Since our initial survey, a few management actions have been implemented. In June, an Executive Order suspending the harvest of shoal bass on the Chipola River was issued. At the recent Commission meeting in October, suspension of harvest for shoal bass on the Chipola River was proposed as a rule and is pending public comment. In addition, we began to collect adult shoal bass to send to the Blackwater Fisheries Research and Development Center to serve as brood stock for supplemental stocking. Currently, 19 shoal bass are being held at the hatchery facility. Fin clips have been sent to the genetics lab in Saint Petersburg to be tested for genetic purity. A multiyear stock enhancement study is slated to begin in spring of 2020. Additional research to evaluate changes in river habitat before and after the storm is also anticipated.

Dorsal Spine Excision and Acute Survival of Largemouth Bass in Florida

By Summer Lindelien

In Florida, Largemouth Bass (LMB) are mainly aged by interpreting annular rings (i.e., annuli) deposited in sagitta otoliths, but extraction can only be accomplished via lethal dissection. Development of non-lethal aging techniques would be a stepping-stone for new research. For example, FWC partners with bass anglers through TrophyCatch, tournaments, and tagging studies which largely, if not explicitly, involve catch and live-release of LMB. Incorporating a non-lethal aging method in these activities would increase the breadth and application of data collected by anglers and scientists; thus, it would be a vital tool for LMB management and conservation in Florida.

Our current non-lethal aging investigations are focused on dorsal spines III–V. Dorsal spines are accessible, easy to remove and process, and when cross-sectioned they can provide relatively precise and accurate ages. The initial step towards implementation was to evaluate the assumption of non-lethality of dorsal spine removal. The objectives of our study were to 1) determine the effects of dorsal spine excision on LMB survivability, and 2) determine if LMB size affects survival following dorsal spine excision.

To evaluate survival after dorsal spine removal, we collected 36 wild LMB across a range of sizes (30–57 cm total length; TL). For positive fish identification, we implanted each LMB with a passive integrated transponder tag and associated them with a weight (g) and TL (mm). After transporting the LMB, we randomly established them in six identical 1200-gallon outdoor tanks where they acclimated for a week. Next, we removed dorsal spines III–V (n = 18) with a pair of cutting pliers and surgical scissors. During the experiment, each tank was occupied by three LMB with excised dorsal spines and three with no excised dorsal spines (i.e., controls). We fed LMB a mixture of wild-caught crayfish, tadpoles, and Bluegill, which were evenly apportioned among tanks at each feeding.

An FWC biologist removes dorsal spines III-V on a largemouth bass.

Over the 35-day study, no mortalities were observed for LMB with excised dorsal spines, and experiment-wide survival was 0.94. Survival was not affected by LMB size, so we proceeded to look for differences in survival between groups without the effect of TL. Ultimately, survival was not different between excised and non-excised LMB (p = 0.15). Despite LMB being fed throughout the trial, all fish exhibited a significant decrease in weight after the study (p < 0.001). On average, LMB lost 105 g, but there was not a significant difference in weight loss between treatment groups. The areas of excision healed with no visible wounds or sublethal effects; however, we noted some LMB with potential handling sores on other parts of their bodies. Consequently, proper care and handling of fish should be kept in mind moving forward with this non-lethal aging technique.

Our current research is focused on continued validation of dorsal spine aging accuracy and precision in LMB across a diverse suite of Florida waterbodies: Lake Griffin, Stick Marsh/Farm 13 Reservoir, Fellsmere Reservoir, L-67A Canal, Escambia River Marsh, and Apalachicola River. As our accuracy is better documented, removal of dorsal spines likely will be taught to fisheries biologists and citizens who handle trophy-bass (≥ 3.63 kg) frequently, allowing an avenue for collection of age data without sacrificing bigger LMB.

FWC biologists designed and constructed an aeration system for 36 largemouth bass held in six 1,200 gallon tanks during a 35-day survival experiment.

“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.