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Recruitment of Juvenile Striped Bass in the Roanoke River, North Carolina, as Related to Reservoir Discharge
Author(s) -
Rulifson Roger A.,
Manooch Charles S.
Publication year - 1990
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/1548-8675(1990)010<0397:rojsbi>2.3.co;2
Subject(s) - morone saxatilis , fishery , juvenile , environmental science , hydrology (agriculture) , bass (fish) , hydroelectricity , streamflow , geography , discharge , drainage basin , ecology , geology , biology , geotechnical engineering , cartography
A multiagency committee was established to examine potential effects of reservoir management and hydroelectric power activities in the lower Roanoke River, North Carolina, on downstream resources and their users. Striped bass Morone saxatilis was selected as a key species because of the extensive long‐term data base on spawning activity and nursery utilization established in the late 1950s. Specifically, the juvenile abundance index (JAI) values for young‐of‐year striped bass in Albemarle Sound (1955–1987) were compared to preimpoundment (1912–1950) and post‐impoundment (1955–1987) flows of the Roanoke River during the spawning season (1 March–30 June). Recruitment was best (JAI > 5.0) for years in which river flows were low to moderate (5,000–11,000 ft3/s) and was poor (JAI < 5.0) when flows were very low (3,900–8,100 ft 3 /s) or high (10,000 ft 3 /s or greater) during spawning season. Additionally, the average flow pattern for good recruitment years (JAI > 5.0) most closely resembled preimpoundment flow conditions. Preimpoundment flow patterns were used to develop a recommended flow regime for the lower river (1 March–30 June) to maintain reservoir discharge between the historical 25% and 75% quartiles of the daily flow (i.e., between the 25% low–flow value [Q1] and 75% high‐flow value [Q3]). A modified (negotiated) flow regime (1 April–15 June) accepted by the U.S. Army Corps of Engineers and a public utility was used in regression analyses to characterize patterns in postconstruction reservoir management. Briefly, the number of days during a season that reservoir discharge stayed within the historical (negotiated) Q1–Q3 bounds has decreased significantly over time, indicating that the manner in which the reservoir system is managed has changed throughout the years. Similarly, JAI values have declined with time, especially for the period 1977–1987, when the 10–year average was only 0.81. The JAI values were divided into four categories (< 1 1.0–4.9, 5.0–9.9, and ≥ 10); analyses indicated that the years of lowest JAI values were also those with the fewest days in which river flow was within the Q1–Q3 bounds. Striped bass egg viability showed similarly declining trends: for the period 1960–1969, viability was 90% and flows stayed within the Q 1–Q3 bounds over 50% of the days; during and after 1978, mean egg viability was less than 50% and days within the Q1–Q3 bounds averaged 27%. The committee's recommendations for a controlled flow regime resembling preimpoundment conditions were accepted by the U.S. Army Corps of Engineers and the public utility for 4 years (beginning in 1989), during which studies will be conducted to monitor the outcome. The flow regime allows the new set of conditions to operate within the guidelines of the original license from the Federal Energy Regulatory Commission.