State agency restores a struggling fishery, answers a few questions
Many crappie populations are notoriously erratic — one or maybe two strong year-classes are often followed by one or more weak year-classes.
This variability has been attributed to reservoir water levels during and after the spawn, the amount of water flowing through the reservoir at different seasons, availability of food, and predation, possibly even by the previous year-class of crappies. In general, crappie abundance is determined by the spawn and survival of the young-of-the-year.
It would seem that crappie stocking could be used to smooth out the dips in recruitment, but stocking to supplement crappie populations has generally been unsuccessful. White crappies stocked into Lake Chicot and six 140- to 1,250-acre impoundments in Arkansas failed to increase crappie abundance. Evaluations of crappie stocking in several Tennessee reservoirs achieved mixed results.
But success was achieved in North Carolina’s Lake Hickory.
The problem
Lake Hickory, a 4,100-acre impoundment in western North Carolina, had historically supported a popular black crappie fishery. Supporting anglers’ complaints, North Carolina Wildlife Resources Commission biologists documented a steady decline in trap-net catches of black crappies from a peak of 8.3 fish per net night in 1999 to 0.4 fish per net night in 2006.
Factors known to affect crappie populations in other waters — hydrology, changes in primary production, loss of spawning habitat, and angler harvest — did not seem to be at play. Biological data pointed to a lack of crappie recruitment. To restore the popular fishery and to test whether crappie recruitment was the problem, the NCWRC began stocking black crappie in 2007.
The approach
The target stocking rate was 20 crappies per acre, or 80,000 per year. The fish were stocked in late summer at approximately 2 to 2½ inches long. The actual stocking rate during 2007 to 2012 varied from 5 to 25 fish per acre, averaging 15 fish per acre.
All fish stocked were marked by immersion in an antibiotic, oxytetracycline, that is incorporated into bony tissue, including otoliths used to age fish and assign year-class, and fluoresces when the marked tissues are illuminated with ultraviolet light. This process allowed biologists to identify stocked fish and evaluate the survival and contribution of the stocked fish to the black crappie population up to several years after stocking.
Crappie were sampled with trap nets in the fall. Fish were measured, counted and otoliths removed for aging and detection of marks signifying stocked fish.
The results
Across all six years, marking success was 96% to 100%. Initial survival after stocking (24-hour survival) was greater than 96% in four years and greater than 79% in the other two years.
The contribution of the stocked crappies — the proportion of stocked fish in fall trap-net samples — varied among stocking years, but stocked crappies were present in almost all samples and across all age-classes. In more than half the age-specific samples, stocked crappies were at least 50% of the crappies collected.
The stocked crappies increased the trap-net catch rates by 29% to 41%.
Although not a component of the study, the reported results suggest a positive correlation between the number of crappie fingerlings stocked and contribution to a year-class. The higher contributions to a year class occurred in the years of higher stocking
Angler catch rates were not monitored after stocking began (an unfortunate shortcoming), but comments from Lake Hickory crappie anglers and guides support increased crappie catches after stocking began.
Lessons learned
Unlike most other crappie stocking efforts that reported no or inconsistent benefits, this stocking effort can be considered successful. And the benefits were evident year after year. Why?
Introduced alewife and white perch may be part of the problem. Both of these non-native fish were illegally introduced into Lake Hickory in the late 1990s or early 2000s. Both fish are potential competition for native fish, and both are also potential predators of young crappie. Alewife, in particular, heavily consume larval fish. Expanding populations of these invasive species could account for the rather sudden decline in black crappies in Lake Hickory. The increase in crappies from stocking, especially since the crappies stocked were about 2 inches long and less vulnerable to the introduced predators, further implicates these unwanted invaders.
And, indeed, if competition and predation by alewife and white perch is interfering with crappie recruitment, stocking advanced-size crappie is an appropriate solution. Unfortunately, both of these introduced fish will be impossible to remove, making stocking advanced-size crappies an expensive and long-term burden on NCWRC.
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