Biology of nonindigenous white perch and yellow bass in an oxbow of the Missouri River.

Abstract

I investigated population dynamics, age and growth, reproduction, and feeding habits of nonindigenous white perch (Marone americana) and yellow bass (Marone mississippiensis) in Browning Oxbow of the Missouri River. I collected 367 white perch and 371 yellow bass from April 1998 to May 1999; trap nets yielded higher catch per unit effort than gill nets or seining. Total catch per unit effort did not vary seasonally. White perch collections were predominantly 'stock (13.0 to 19.9 cm TL) and quality (20.0 to 24.9 cm TL) length fish, with mean relative weights (Wr) of 113 and 93, respectively. Yellow bass were predominantly quality (18.0 to 22.9 cm TL) lengths, with a mean Wr of 100. Male/female sex ratios for white perch and yellow bass were significantly different from 1: 1, with more females than males for both species. Populations of white perch and yellow bass were mainly age-2 and age-3 individuals, and I caught more older females than males for both species. Growth rates were highest in the first two years, and decreased thereafter. White perch and yellow bass successfully reproduced in the oxbow in April and May, as evidenced by gonadosomatic index values and presence of young-of-the*year (YOY). Most age-l male and age-2 female white perch and yellow bass were sexually mature, and males ripened earlier in spring than did females. Fecundity estimates were high for both species, suggesting that white perch and yellow bass might quickly overpopulate this small impoundment, and that stunting could result. Diet of YOY was mainly zooplankton, and adult white perch and yellow bass fed primarily on aquatic insects and fishes. White perch fed heavily on dipterans in spring and summer, but switched to feed on fish in fall and winter. Yellow bass fed heavily on dipterans in spring, summer, and fall, and switched to feed on fish in winter. The nature of white perch and yellow bass diets raises the possibility for competition with indigenous fishes.