Possible Competitive Effects of Two Introduced Planktivores on White Crappie

Field and laboratory experiments were conducted to investigate possible competitive effects of the introduced species inland silversides (Menidia audens) and threadfin shad (Dorosoma petenense) on the native white crappie (Pomoxis annularis) population in Thunderbird Reservoir, Oklahoma. Field collections of zooplankton and stomach analyses were augmented by laboratory feeding experiments with the introduced planktivores and white crappie, alone and in combination. Field samples indicated that silversides, shad, and crappie, showed positive selectivity (Strauss' L) for Daphnia. Feeding studies in the laboratory corroborated this finding for all species tested individually. However, in feeding experiments, white crappie switched to an indiscriminant diet when in the presence of silversides or threadfin shad. These findings indicate that the introduced planktivores are competing with white crappie and could be a possible contributing factor to the poor growth rates seen in the crappie population of Thunderbird Reservoir.

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