Bias from Age-grouping Black Crappie by Length-frequency as Compared to Otolith Aging

Eighteen hundred and thirty-four black crappie (Pomoxis nigromaculatus) were collected from the St. Johns River, Florida, in late winter and early spring, 1982 to 1985. Differences in numbers and growth rates of males and females collected were not significant (P > 0.05). Fish were separated into age groups using length-frequency distributions and by counting annuli on otoliths. Only 2 distinct age groups were discernible by length-frequency analysis, whereas 6 to 8 groups were identified by otolith aging. Mean lengths of age groups obtained from lengthfrequency were overestimated 3 of the 4 study years when compared to otolith aging. Length range overlap from otolith aged groups varied from 15.2% to 100% and averaged 69.3%. Year class overlap occurred as early as years I and 2 and indicated a bias when relying on length-frequency evaluation alone.

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