Crappie Science

Crappies for the most part remain abundant in the face of sustained fishing pressure from lots of avid anglers. And while we might all like to catch bigger crappies, most are eating-size, so it's not a critical concern. Moreover, attempts to improve the size structure of crappie populations with regulations have met with little success. Crappie spawning and recruitment have long been perplexing as well, but as long as they're not scarce, we tend to let nature take its course.

Crappie Biology

Early in the last century, specialists in fish behavior mapped out the basic life history of our two crappie species, noting differences in behavior in reservoirs and shallow lakes, and among waterways at various latitudes. Descriptions of spawning behavior and prey preferences also were conducted, establishing the baseline of information we rely on when planning fishing strategies. Yet, new findings continue.

Spawning Schedule: It all starts with the spawn and readers near southern waters can look for top action this month. But did you know that crappies have been known to switch-hit and spawn in fall?

Over the years, we'd heard reports of bass and crappies spawning in fall, but this had never been scientifically documented until biologists with the Florida Fish and Wildlife Conservation Commission found small juvenile crappies in their fall sampling at Orange Lake. Curious about their origin, they collected more samples and aged the young fish by looking at the daily growth rings on their otoliths.

The 2- and 3-inch crappies they collected in December had hatched between the first and fourth week of October. No good explanation of this phenomenon has been forthcoming, though rising water levels in fall were considered a possible trigger.

Spawning-Site Fidelity: Movement studies have documented fish of several species returning to the same area to spawn year after year. Where fish use the same spawning area each year, protecting that habitat is critical to keep populations healthy.

Toward this end, Nebraska researchers examined whether crappies display spawning-site fidelity at Sherman Reservoir, a 2,850-acre Nebraska irrigation impoundment known for good fishing. They captured crappies in trap nets from 5 coves in May and marked them with color-coded tags over several years.

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Adult crappies demonstrated cove fidelity within and among spawning seasons. Over 80 percent of tagged fish were captured in the same cove during the same spawning season, and over 70 percent were recaptured in subsequent years in the same cove. The researchers concluded that crappies sought specific coves in which to spawn, even when similar coves and substrates were available nearby.

Also of concern for spawning success is a report from the Minnesota DNR about effects of lakeshore development on nesting by black crappie and largemouth bass. On three lakes, biologists noted nest locations and proximity to docks and developed shorelines as well as canopy cover and aquatic vegetation.

Crappies were more likely to nest along undeveloped shorelines with canopy cover and aquatic vegetation. Nests along developed banks were deeper than those found on undeveloped shorelines. Loss of emergent vegetation, which often occurs with development, could cause crappies to spawn in concentrated areas containing preferred habitat. This could lead to weather-induced spawning failure if locations weren't protected from waves or wind, or could lead to overharvest of spawning fish by anglers. Results showed crappies were more vulnerable than bass to shoreline development.

Hybrid Crappies: Investigations in reservoirs containing both black and white crappies have found high incidence of hybridization. For example, over half the fish collected in Douglas Reservoir, Tennessee, were hybrids, as were 21 to 29 percent of fish in Lake Weiss, Alabama.

Hybridization in natural lakes hadn't been examined until age-growth studies in Minnesota found some fish growing unusually fast. Hybrid vigor, the tendency of first-generation hybrids to grow very fast, was suspected in these lakes in the southern part of the state where the two species coexist.

Researchers collected fish from 22 lakes and, using DNA testing, found hybrids in 20 of them. Minnesota DNR biologists had been calling most of these F1 hybrids black crappies, skewing growth rate evaluation Only the first generation showed hybrid vigor, a common situation with animal crosses.

Management

Length Limits: Anglers often rue the good old days when big slabs reportedly were more abundant. For the past 25 years, fishery managers have looked at ways to increase numbers of large crappie. After regulations seemed rather successful in Missouri in the mid-1980s, other jurisdictions evaluated them.

The latest evaluation comes from Minnesota, where anglers and biologists felt length limits might have benefits, due to lower natural mortality and increased longevity of crappies there. On the other hand, slow growth of Minnesota fish might nullify any benefits.

Researchers with the Minnesota DNR chose 4 study lakes, where 9-, 10-, and 11-inch minimums were imposed, and sampled other lakes with no special regulations (only the statewide 10-fish bag limit) for comparison. Although data from 15 years were evaluated, improvement was noted in only one case.

In a couple lakes, illegal harvest could have negated any benefits of the regulations. But at the lake where no illegal harvest was detected, size structure did not improve. Nearby reference lakes continued to produce better fishing.

Water Level Management: Crappies build nests in shallow bays and male fish guard eggs and fry, so low water levels might hurt recruitment, the process of refilling the ranks of catchable fish. Water level rises prior to the spawn may be beneficial, flooding shoreline cover and adding nutrients that boost zooplankton that then feeds larval crappies.

Researchers at Auburn University have conducted several investigations of hydrological effects on recruitment of black and white crappies in Alabama reservoirs. The relationships were complicated but in impoundments with short retention times (fast flows through the reservoir), wet winters that raised water levels and increased discharge rates through mid-April encouraged strong year-classes, although there were exceptions.

Research on Ohio reservoirs suggested, in contrast, that fertility was most closely related to crappie recruitment. More fertile lakes tended to produce more crappies. There didn't seem to be a relationship with water levels, although fluctuations were less than in Alabama impoundments and retention times were longer, making these waters function more like natural lakes.

So crappies remain somewhat inscrutable for fishery managers, as well as for anglers planning a spring outing. Good conditions — slowly rising and warming water, mild weather, and light wind — mean lots of fish and some slabs. But drop the temperature, throw in a northwest wind, and lower water levels and you scratch all day for a handful of fish.

Make the most of good bites, releasing fish not needed for a dinner or two and particularly the largest fish. Each angler can contribute to keeping populations strong by selective harvest, urging biologically based regulations, and working to maintain optimal habitat in natural and less natural waters.

Recruitment Puzzle

Management Notes — Crappies are notorious for inconsistent year-class strength. Some lakes and reservoirs produce strong year-classes only every 3 to 4 years. As these crappies grow to catchable size, fishing is temporarily great until natural mortality and harvest take their toll, then fishing declines. Some waters have more consistent annual production of fewer crappies, while others regularly produce many young leading to high-density slow-growing populations.

Year-class strength is set by reproductive success and recruitment, the process by which fish are added to the catchable population. Spawning success in crappies is tied to habitat quality, as well as environmental conditions during the spawn and egg development, such as water level and weather.

Once crappies hatch, several factors affect survival during the first year of life, such as availability of food for the young, predation, temperature and wind, and hydrological conditions. High water levels, high reservoir discharge, reservoir productivity, predator density, and zooplankton abundance have been correlated to survival of young crappies. Recruitment also has been shown to be related to spawning stock size in some instances.

Highly variable year-class strength is challenging to fishery managers because these types of populations are unpredictable and generally don't respond well to harvest regulations. However, some control over crappie populations has been obtained through manipulating water level, cover, predator density, and by imposing length and creel limits. Relationships between recruitment and spawning stock size suggest that regulations may improve recruitment in fisheries where low numbers of spawners limit production.

Rob Neumann

Size Affects Catchability

Anglers are best at catching middle-size crappies, according to a tagging study in 3 states by researchers at Mississippi State University.* Dr. Steve Miranda and Brian Dorr tagged about 3,000 black crappies and a similar number of whites, ranging from 8 to 16 inches, in 5 bodies of water.

Tag returns from anglers showed the lowest catch rate for small fish of both species, gradually increasing from 8 to 12 inches, with catchability declining for the biggest crappies. Crappies from 10 to 13 inches were most likely to be caught. Small white crappies were particularly elusive and the largest black crappies also evaded anglers. Fishing tackle and method, and differences in behavior and habitat among different sizes apparently affected catch rates.

For fishery managers, the results provide information for setting length limits. To cut harvest substantially, a protected slot-length limit of 10 to 13 inches should be effective, while a length limit of 10 inches may be ineffective, at least in the region studied.

*Miranda, L. E., and B. S. Dorr. 2000. Size selectivity of ­crappie angling. N. Am. J. Fish. Mngt. 20:706-710.