FWC biologist preparing to implant an acoustic telemetry tag into a bass at Kingsley Lake.
FWC biologist preparing to implant an acoustic telemetry tag into a bass at Kingsley Lake.
FWC biologist preparing to implant an acoustic telemetry tag into a bass at Kingsley Lake.
FWC biologist preparing to implant an acoustic telemetry tag into a bass at Kingsley Lake.
FWC biologist conducting radio telemetry searches at the Harris Chain of Lakes.
FWC biologist releasing a tagged bass at the Harris Chain of Lakes.
FWC biologist cradling a bass recovering from being implanted with a radio telemetry tag at the Harris Chain of Lakes.
Largemouth bass commonly reach sizes in Florida that dwarf those in many other parts of the world where they are native or introduced. This trend is in part due to the long growing season in a warm subtropical climate and the natural fertility of Florida’s abundant freshwater lakes, but largely due the unique genetics of largemouth bass in Florida that allow many of them to grow to epic sizes. Their genetic character is distinct enough that FWRI geneticists advocate they are separate species (Micropterus floridanus) from largemouth bass native to the rest of North America (M. salmoides). Thus, catching trophy bass, or at least having the chance to catch one, is a major component of the attraction and allure to freshwater fishing in Florida.
To promote trophy bass fishing and conservation in Florida, the Florida Fish and Wildlife Conservation Commission (FWC) launched TrophyCatch in 2012. TrophyCatch rewards anglers for catching, documenting and releasing trophy bass while engaging anglers as citizen scientists who help the FWC build a long-term dataset of where and when trophy bass have been caught across the state. Trends or anomalies in these data may help steer FWC’s research biologists to develop new studies on largemouth bass or other species.
Kingsley Lake emerged from the TrophyCatch data as an unexpected and prolific producer of some of Florida’s largest bass. These bass were thought to be unusually old, and FWC biologists hypothesized their size and age might be linked to the lake’s unusual depths, which exceeds 40 feet deep across much of the lake’s offshore waters. If the water column at Kingsley Lake underwent thermal stratification during summer, bass there might be able to select temperature zones that maintain their metabolism closer to optimal levels compared to bass in shallower lakes that grow excessively hot, top-to-bottom, during much of the summer. Researchers working at the Harris Chain of Lakes (HCOL) had similar interests of learning more about trophy bass behavior and longevity. Communication among biologists led to hypotheses regarding differences between Kingsley Lake and lakes, such as those on the HCOL, that were more representative of Florida’s shallow-vegetated waterbodies.
Based on those discussions, FWC biologists developed two telemetry studies to learn more about the life history of bass in Florida and how these fish interact with their environments. Biologists specifically targeted the largest and oldest segment of the population because trophy bass are revered by anglers. One of the goals in this study was to document differences in lake characteristics and how the large bass behave to better understand the factors associated with Kingsley Lake bass living longer and growing to larger maximum sizes. By better understanding some of the environmental and habitat conditions that are linked to trophy bass occurrence at Kingsley Lake and HCOL, FWC can better manage fisheries for trophy bass across the state.
FWC biologists used two types of telemetry tags – acoustic and radio – to track the movements of bass. At HCOL, bass were collected by boat electrofishing, which temporarily immobilizes fish in freshwater so they can be netted. At Kingsley Lake, biologists collect bass via hook-and-line sampling. For both types of telemetry tags, biologists surgically implanted them into the body cavity of study bass. The tags were about the size of an AA battery, so the incisions were less than one inch long and required 3–4 sutures to close. What distinguished the two types of telemetry tags used was the way that they transmitted information to biologists. Because of Kingsley Lake’s smaller size (1,700 acres), biologists used acoustic telemetric tags there and were able to install a grid of acoustic receivers that covered the entire lake. The acoustic tags also included depth and temperature sensors, which provided near-continuous depth and temperature recording for tagged fish during the study. Collecting these data required biologists to routinely retrieve the receivers and downloaded the tag detection logs. Bass at lakes Eustis (one year) and Dora (four years) were implanted with radio telemetry tags because these two lakes were much larger and radio telemetry allows for much faster searching when relocating tagged bass. The radio tags contained a sensor that measured temperature and one that monitored movement and would alert biologists if the bass died and ceased moving. There, biologists conducted weekly searches to find all radio tagged bass and recorded GPS locations, temperature and habitat data for each one.
Besides water temperatures collected from the actual tagged fish locations, researchers collected temperature and oxygen profiles at fixed sites for each lake during the summer months.
The study at Kingsley Lake has been completed, but biologists plan to continue tagging more trophy bass at the HCOL and are considering transitioning the focus to Lake Apopka, which has recently experienced substantial gains in habitat and fishing effort.
Biologists confirmed that bass at Kingsley Lake reach exceptionally old ages for bass in Florida. Age estimates for several bass found dead and donated by lake residents were 14–16 years old. Conversely, bass aged from Lake Eustis, Dora and other lakes within the HCOL had a maximum age of 11 years old. Although researchers don’t have evidence that Kingsley Lake has higher growth rates, a greater average longevity may allow large bass more years to grow and a subset of trophy bass to reach sizes that are almost never achieved at the HCOL. For example, the TrophyCatch database includes 17 bass caught over 13 pounds at Kingsley Lake (1,700 acres) compared to zero bass over 13 pounds caught at the HCOL (76,000 acres). Therefore, longevity is an important factor in bass attaining trophy sizes over 13 pounds.
Key differences between the two waterbodies may help unlock the mystery of Kingsley Lake bass living to much older ages. Mapping of the lakes revealed that nearly 50% of Kingsley Lake’s area had depths of 24 feet or greater, with a maximum depth of 82 feet; compared to Lake Dora, which has a maximum depth of 15 feet. Water quality monitoring at each lake revealed that the water column had thermal stratification at Kingsley Lake compared to Lakes Eustis and Dora where the temperature and oxygen did not decline substantially with depth. Information from tagged trophy bass showed that bass at Kingsley Lake do sometimes select for cooler layers within the water column. This was most prevalent during late spring and early summer and may be advantageous for bass recovering from spawning season. Compared to the telemetered bass at the Harris Chain of Lakes, Kingsley Lake bass inhabited cooler water 90% of the time, and temperature differences were most pronounced in spring and early summer, when Kingsley Lake bass averaged about 4°F cooler temperature. This temperature difference was a little less than biologists expected, but much of Kingsley Lake’s deepest and coolest water becomes devoid of oxygen by mid-summer, reducing the overall available thermal refuge. Studies have found (including FWC telemetry work) that bass endure the most stress and mortality during post-spawn and summer months in Florida. With bass at Kinsley Lake having access to and using the cooler strata of water during this season of high stress, it is likely this results in reduced natural mortality each summer; allowing for higher longevity to attain larger maximum size.
Although the sample sizes are low and mortality was not the primary objective at Kingsley Lake, researchers did observe much higher annual mortality at Lakes Eustis and Dora (87%) compared to Kingsley Lake (20%). At Lakes Eustis and Dora, researchers confirmed the fate for 48 tagged trophy bass and 29% were caught by anglers which resulted in a total of 17% fishing mortality (combination of harvest and release mortality). Natural mortality at the HCOL was 70% and of those that died from natural mortality or release mortality, all besides 1 died from April through September. This study helps confirm the high mortality season for trophy bass in Florida as water temperatures approach 90°F; along with providing more evidence how refuge from these extreme conditions during the hot summer months may affect mortality rates.
This research was funded by boaters and anglers through the federal Sport Fish Restoration Program. The FWRI Freshwater Fisheries Research biologists who led this study worked closely with Division of Freshwater Fisheries Management biologists. Camp Blanding Joint Training Center allowed the researchers access to Kingsley Lake through U.S. military property.
Results from this study could inform future fisheries or habitat management actions. Habitat use patterns could help fisheries managers determine the best placement for offshore fish attractors or help prioritize areas and habitats for restoration activities. Knowledge of the value of thermal refuge in deep lakes could be used to seek additional lakes with bathymetry and water column stratification similar to Kingsley Lake to create angler access or pursue trophy bass management strategies. FWC could promote the habitat use patterns documented in this study to anglers, making them more informed of bass behaviors and perhaps leading to more angling success.