July 22, 2024
By Dr. Hal Schramm
Crappie anglers, like all anglers, want to catch bigger crappies. Many assert that increasing fishing effort, especially the numbers of anglers employing superefficient techniques like spider-rigging, are depleting crappie numbers before they grow to large size. The increasing use of forward-looking sonar like Garmin Panoptix, allowing anglers to target the biggest fish and increase size-selective harvest, adds to the fury.
Fishery managers work hard to satisfy anglers, but crappie populations, both black and white, sometimes seem to defy management. As management efforts increase, however, it’s becoming clear that not all crappie populations are capable of consistently producing slab crappies, while other populations seem able to sustain quality crappies despite high harvest.
Crappie Management Timeline Crappies began to attract fishery management attention in the 1970s. The most frequent problem at the time was what Iowa DNR fishery biologist Larry Mitzner called “small crappie syndrome”—the occurrence of populations composed largely of too-small-to-keep crappies. Many, but not all, of these fisheries were in small impoundments and natural lakes. The prevailing management strategy was to thin the populations, allowing fewer fish to share the finite food supply and grow faster and larger.
This is a common and valid management strategy for several intensively managed freshwater sportfish, but efforts to reduce populations by poisoning (usually with rotenone) or mechanically by trapping or netting were time-consuming, expensive, and would be sheer folly in large waters. And any beneficial effect, if attained, usually was short lived. Some success was achieved by stocking crappie predators like saugeyes, but maintaining an effective predator density is a challenge.
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Managers then turned to prey management to provide more forage to fuel faster growth to larger sizes of the often-abundant crappies. Although limited to waters in the southern half of the United States due to their intolerance of water temperatures below 50°F, threadfin shad was the prey of choice. Unlike the more widespread and cold-tolerant gizzard shad, threadfin shad only grow to 5 or 6 inches. More importantly, threadfin shad from the spring spawn mature and spawn in late summer of the same year, thus providing a steady supply of bite-size energy packets for both small and large crappie s.
Establishing threadfin shad populations achieved some positive results like a 2.5-inch increase in length of age-1 crappies in Osage State Fishing Lake in Kansas, but trials elsewhere failed to achieve beneficial effects. Along the way, some biologists found that zooplankton-chomping threadfin shad competed with and hindered the zooplankton-dependent early life stages of crappies.
In the late 1970s, managers began to think about restricting harvest, the antithesis to the prevailing wisdom of thinning these prolific fish to grow bigger crappies. Crappie population studies by Missouri Department of Conservation fishery biologist Mike Colvin at four large Missouri reservoirs, all heavily fished for crappies, found relatively fast growth (9 inches by age 3) and few fish older than age 3. Angler exploitation rate, the portion of the catchable population removed by angling, was 50 percent for age-2 crappies but jumped to 80 percent for age-3 crappies. Colvin reasoned that the small size structure of the crappie populations resulted from high angler harvest.
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Beginning in 1976, Colvin led a project to evaluate both minimum length limits (MLLs) and reduced harvest limits on five of Missouri’s larger reservoirs. He used a yield-per-recruit model (see the sidebar below on how these models work) to evaluate different harvest restrictions. The model predicted delaying harvest to age 3 would result in fewer crappies harvested, but the yield in weight to anglers and mean size, density, and biomass of crappies in the population would all increase.
Using the model predictions for guidance, creel limits were reduced from 30 fish per day to 10 or 15 fish per day on the test reservoirs. A 10-inch MLL was also implemented on two of the reservoirs. Population responses among the reservoirs varied, partly a consequence of varying recruitment and, subsequently, year-class abundance—but consistent among all reservoirs, the anglers were catching fewer but larger crappies and achieving greater yield (pounds of fish per day) as was predicted by the models.
Survival of crappies increased in the two reservoirs with the MLLs but not at lakes only with reduced creel limits, suggesting length limits were more effective than reduced creel limits. Noteworthy is that growth rate did not decline despite the increased density of crappies, shunning the widely held belief that high abundance limited growth.
But these were large reservoirs, not the small impoundments and natural lakes where overabundance is more likely. A study in 41 Ohio reservoirs found crappie size structure and growth rate increased in large (greater than 2,500 acres) reservoirs but declined in smaller waters after implementation of a 9-inch MLL. Population thinning is still a viable approach for small waters.
An Angler’s Guide to Yield-Per-Recruit Population Models As the name implies, these models estimate how many harvestable crappies are produced by a fixed number of fish recruited to the population. Recruits to the populations are usually estimated as the abundance of age-1 crappies, fish that have survived the larval stage and their first winter, a time of usually high mortality.
The mathematical equations for these population models can be intimidating, but operating them is the job of the fishery scientist. Of importance to the engaged angler, though, is how the essential population variables interact over time to estimate the end result: what harvest regulation produces more large crappies?
Recruitment adds fish to the population, mortality removes them. Mortality is a result of capture and harvest by anglers (exploitation rate, fishing mortality) and natural causes (natural mortality) like diseases and predation. Starting with, say, 1,000 age-1 crappies, the number is diminished by natural mortality until they reach a harvestable size, at which point the numbers are reduced by natural mortality plus fishing mortality.
In a fishery with a high minimum length limit (MLL), the number of fish available for harvest is steadily reduced by natural mortality for as long as it takes for the fish to grow to legal size. If growth is slow, losses to natural mortality are high and few fish survive to reach the MLL and be harvested. If growth is rapid, natural mortality has had less time to reduce the population, and more fish are available for harvest.
Mortality accelerates due to exploitation when fish surpass harvestable size or the MLL. High levels of exploitation above the MLL also reduce yield, because the fish are harvested before they grow to their potential, what biologists call growth overfishing.
Accurate estimates of growth rate and mortality (natural and fishing) are important for modeling crappie populations. The Modeling Era Population modeling techniques improved and their application expanded in the 1990s. An astute fishery biologist with a laptop computer can now forecast the potential effects of various harvest restrictions. But, and that’s a big but, the variables needed are not easily measured accurately. The various forms of population models rely on estimates of growth rate (the length increment added each year), mortality rates (the number of fish that die from natural and fishing mortality), and the exploitation rate (the proportion of the population removed by fishing).
Growth rates can be accurately assessed from the age of a fish (easily determined from otoliths, bones removed from the inner ear) and the length of the fish at capture. Total mortality rate is easily estimated from statistical analysis of numbers of fish in each age class, but this requires a representative sample, one that collects each age group of fish in proportion to their actual abundance, and assumes constant recruitment. Crappie sampling gears often are size (and, thus age) selective, and crappie populations are notorious for variable recruitment, often resulting in uncertain estimates of total mortality.
Exploitation is estimated by tagging a large number of fish in the population and then relying on anglers reporting all tagged fish caught, a process that takes at least one entire fishing season and requires full cooperation of anglers. Tag reporting rate is often less than 60 percent and results in less certain exploitation estimates.
All told, population models are a useful tool for forecasting trends and evaluating different harvest strategies, but they are not accurate predictions.
Drs. Micheal Allen and Steve Miranda at Mississippi State University rigorously explored crappie population models to evaluate 8- and 10-inch MLLs to improve the size of crappies available to anglers. They assembled all available estimates of white crappie growth, annual mortality, and angler exploitation rates from throughout their range (see the table below). These models predict yield, the weight of crappie harvested. More yield means more large crappies.
Regardless of growth rate, yield was low for both length limits at all rates of exploitation when natural mortality was above 40 percent. For crappies with average growth rate, the 10-inch length limit increased yield when natural mortality was 20 percent, a rare occurrence. For fast-growing crappies, the 10-inch length limit increased yield at 20 percent and 30 percent natural mortality. The take-home from this significant study: high MLLs can improve yield only when growth is fast and natural mortality is low. Studies in Tennessee indicate crappies attaining 10 inches by age 3 is sufficiently fast growth for a 10-inch MLL potentially to be effective.
The models also underscored a common and unsurprising effect of fishing known as “growth overfishing.” Even with fast growth, low natural mortality, and a high size limit, the size of the fish declined as exploitation increased. The more fish that are harvested at 10 inches, the fewer fish will survive to 12 inches, even when natural mortality is low.
There is a hidden bonus from a high MLL when appropriate; that is, in lakes with fast growth rate and low natural mortality. Inconsistent recruitment, for example, a strong year-class followed by one or more weak year-classes, seems to be the norm for many crappie populations. In these lakes, a high MLL, especially if coupled with a reduced creel limit, can extend the presence of the strong year-class and help mitigate the downturn in fisheries that would occur when the weak year-classes enter the fishery.
The trick to effective crappie management is finding the balance between size and yield. The computer makes that easy if the biologists have the time and resources to accurately measure growth rate, mortality, and exploitation. But the angler is the ultimate arbiter of a good regulation. There is no average angler. Some want big crappies and are willing to forego numbers. Others are happy with a cooler of 10-inchers.
But some fisheries are not, due to growth and mortality rates, going to produce 10-inch-plus crappies. A sure recipe for disaster is to implement a size limit intended to improve the size structure of the population, but anglers are catching a lot of crappies just short of the MLL; the anglers are disgruntled, and a usable resource is wasted. And these anglers are more likely to become noncompliant with the regulation, creating enforcement problems.
Some anglers want big crappies, even if the trade-off is catching fewer fish, while other anglers are happy to catch and harvest numbers of smaller crappies for a fine meal. Unlike some reservoirs in Mississippi where 11- and 12-inch MLLs have proven effective, evaluations of 9- or 10-inch MLLs were found either ineffective at improving crappie size or provided insufficient gains to be worth implementing in Alabama (10-inch MLL), Florida (10-inch MLL), Georgia (9-inch MLL, black crappies), Minnesota (9-, 10-, and 11-inch MLLs, black crappies), Ohio (10-inch MLL), Nebraska (10-inch MLL), South Dakota (9-inch MLL), Tennessee (10-inch MLL), and Wisconsin (9-inch MLL).
And there is no average crappie population, even within the same state. Growth, exploitation, and natural mortality rates vary, as shown in the table. No doubt, harvest restrictions tailored to each population may improve the size of crappies caught in some waters, but estimates of the vital rates necessary to evaluate lake-specific regulations are costly to obtain and subject to change over time.
In 1985, Texas Parks and Wildlife Department (TPWD) biologists Dr. Richard Ott and Mark Webb tested and found a 10-inch MLL 25-fish daily bag limit effective on three reservoirs. That regulation was subsequently expanded statewide and, so far, has been effective.
Undoubtedly the fisheries have changed in the 25 years since Ott and Webb’s study, but TPWD biologists remain comfortable with the 10-inch MLL 25-fish bag. After compiling input from biologists statewide, TPWD regional supervisor Marcos DeJesús shared that with natural mortality exceeding 40 percent in most lakes, benefits of a higher MLL are unlikely. Right now, the statewide 10-inch MLL is working, and fish population and fishery declines have not been observed.
Establishing Fishing Regulations: The Florida Model Once upon a time, fishing regulations were established by decree, sometimes based on the inclinations of well-meaning but not necessarily well-informed fishery commissioners or, starting 4 or 5 decades ago, by trained fishery biologists. But this “government-knows-best” practice has been replaced by a process that listens to anglers.
In 2019, the leadership of the Florida Fish and Wildlife Conservation Commission (FWC) recognized the need to review the regulations for the state’s popular black crappie fisheries as part of a comprehensive Fisheries Management Plan. They followed a prescribed protocol. Similar processes are used to promulgate regulations in other states.
Step 1: A management team of fishery managers and scientists, law enforcement, and human dimension specialists was created to oversee the process.
Step 2a: Anglers were asked multiple questions about their fishing preferences; for example, attitudes about current regulations, sizes they want to catch, and acceptable bag limits. Input from a diversity of anglers was obtained via mailed and online angler surveys, during creel surveys, and at announced public meetings (virtual meetings in 2020). Importantly, there was no “agenda;” anglers were not asked to comment on regulations already proposed or considered “biologically necessary.”
Step 2b: Concurrent with seeking angler input, biological data were compiled and analyzed to measure a spectrum of variables needed to fully evaluate the effects of different length and daily bag limits on angler catch and crappie population sustainability.
Step 3: The management team integrated the angler input and biological findings to determine the best regulation that ensured sustained crappie populations and accommodated anglers’ preferences. Through this process, completed in 2021, the management team recommended that no change in the current regulation (no minimum length limit, 25 fish daily limit) would best satisfy the greatest number of anglers.
Step 4: The management team’s recommendation was submitted to the Division of Freshwater Fisheries Management leadership for approval. In August, 2021, the recommendation of no change in regulation was approved.
Step 5: The Division then reported back to anglers to explain how their information was used and why FWC made the decision they made.
Because “no change in regulation” was recommended, the process ended after Step 5. If, however, a regulation change was recommended, two additional steps would have been necessary.
Step 6: Additional public input would be sought via public meetings to measure anglers’ support and opposition to the regulatory change.
Step 7: The proposed regulation and the anglers’ input would be submitted to the FWC’s seven appointed commissioners for acceptance or rejection.
Looking Ahead Despite what appears to some anglers to be unsupportable harvest of crappies, larger lakes and reservoirs continue to provide excellent crappie fisheries with minimal harvest restrictions. Anglers seeking large crappies in smaller waters will be forced to remain in search mode, fishing different lakes until you find the one with a strong year-class just reaching large size—and then trying to keep it a secret.
Bernard Williams, an outdoor communicator and a crappie addict who spends many days on Mississippi’s hyper-productive crappie waters, asserts that there’s a growing practice of releasing truly big crappies and maintains that the smaller crappies are far better eating. How widespread is this new behavior among the usually highly consumptive crappie crowd? Change is always possible.
In-Fisherman Field Editor Dr. Hal Schramm is former leader of the USGS Mississippi Cooperative Fish and Wildlife Research Unit at Mississippi State University. An avid angler and educator on fishery conservation and fishing topics, he frequently contributes to In-Fisherman publications.