Biology of Age-1 and Older Yellow Perch in West-Central Minnesota Lakes

Despite their importance in fish community dynamics, segments of yellow perch Perea flavescens ecology in west-central Minnesota lakes remain unknown. The objectives of this study were to determine population structure, population dynamics, adult yellow perch seasonal ontogeny in diet, and if age-1 and 2 yellow perch used larval fishes as a source of prey. Results from spring trap netting in 1999 indicated that yellow perch in the four study lakes exhibited slower growth than the Minnesota statewide average and rarely reached total lengths of 20 cm. Yellow perch relative weight Wr values were consistently 80 or below, and at the time of sampling (prespawn) should have been at their maximum Wr for the year. Seasonal food habits for adult yellow perch were collected in May, August, and October by electrofishing. Samples were collected from Lakes Blackwell and Freeborn in 1999, while samples were collected from Lakes Brophy and Louise in 2000. In addition, winter samples were collected from Lakes Brophy and Freeborn in February of 2000 under the ice using gill nets and angling. Both mean percent by number, an indicator of prey diversity, and mean percent by weight, a general indicator of energy intake, were calculated for each month. Macroinvertebrates were usually the primary (% by number) prey item selected by yellow perch \u3c20 cm, while prey fishes were commonly the primary (% by weight) prey source for yellow perch ≥ 13 cm. Fish consumption was observed in yellow perch as small as 6 cm. while yellow perch \u3e1 3 cm consumed fish on a regular basis. Prey fish selection varied considerably by season. During the spring, the primary two prey fishes consumed were brook sticklebacks Culea inconstans and johnny darters Etheostoma nigrum. Lepomids became the primary fishes consumed during late summer, fall, and winter months, likely because age-0 lepomids had reached lengths that made them vulnerable to predation by yellow perch. Adult yellow perch were classified by length groups: length group 1 (\u3c1 30 mm), length group 2 (1 30-1 99 mm), and length group 3 (≥200 mm) so resource overlap could be evaluated. Diet overlap between the length groups was low despite all yellow perch being collected from the littoral zone. Diets of age-1 and age-2 yellow perch were determined weekly during May and June and every third week during July and August in 1999 and 2000. Macroinvertebrates were usually the primary (% by weight) prey item selected but at times zooplankton was the primary prey source. Linear electivity values revealed that when zooplankton was selected for, cladocerans were usually selected over copepods. Though prey fishes were rarely utilized as the primary prey source they did appear in diets on a consistent basis. Larval fish consumption was observed by both age groups but was never a substantial part of the diets. Consumption of fish eggs by both age groups was also observed. Ultimately, results from this study can improve our understanding of the role of yellow perch predation in complex littoral fish communities. Regardless, our results provide a step toward understanding the complex nature of yellow perch-bluegill interactions in complex natural lake fish communities