Health and Condition of Trout in the Norfork Tailwater, Arkansas, Following Hypoxic Periods

Health, feeding, and relative weight of brown (Salmo trutta) and brook trout (Salvelinus fontinalis) were assessed seasonally at 2 sites on the Norfork tailwater, Arkansas, to evaluate effects of hypoxic water discharges from Norfork Dam. The upper site was immediately below Norfork Dam and subject to low (<6 ppm) dissolved oxygen (DO) in water releases during summer and fall. Dissolved oxygen recovers to ≥6 ppm before reaching the downstream control site. During fall, the health of brook and brown trout was significantly lower at the upstream, low DO, site than at the downstream, normal DO, site, and at both sites during the spring, normal DO period. Feeding rates of brook trout were also found to be reduced during the low DO period at the upper site. Relative weight was significantly higher for brown trout during the normal DO period in spring probably due to food availability during winter. Current efforts to maintain 4 ppm DO in hydropower discharges from Norfork Dam reduce the occurrence and severity offish kills; however, these efforts are insufficient to provide for trout health or prevent economic losses resulting from a direct loss offish or reduced angling success.

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