Assessing impacts of the Roanoke River Flood Reduction Project on the endangered Roanoke logperch
May 2005 - April 2011
- Corps of Engineers
The United States Army Corps of Engineers (USACE) has contracted with the City of Roanoke, VA to carry out the Roanoke River Flood Reduction Project (RRFRP), a suite of channel modifications. The United States Fish and Wildlife Service (USFEW) has required the USACE to monitor populations of the federally endangered Roanoke logperch (Percina rex) prior to and during construction to estimate the effects of incidental take during the course of the project. The USACE contracted with Virginia Tech and the Virginia Cooperative Fish and Wildlife Research Unit to conduct the pre-construction monitoring, which began in 1992 and continued intermittently through 2003 (see Ensign and Angermeier 1994, Ensign et al. 1999, Galbreath et al. 2001, Roberts and Angermeier 2004). The primary goal of the pre-construction monitoring was to obtain baseline data on population density of Roanoke logperch, habitat quality, and water quality at selected sites within the RRFRP reach prior to initiation of construction activities. The RRFRP is now in its construction phase, which is expected to take 4-5 years. This phase requires a revised monitoring protocol. In particular, based on analyses by Rosenberger and Angermeier (2003) and Roberts and Angermeier (2004), the USFWS recommended several changes in the previous monitoring protocol, including a) constraints on when electrofishing should be conducted, b) developing census methods for young-of-year (YOY) logperch, and c) collecting data to enhance understanding of logperch stock-recruitment relations. The goal of monitoring now is to assess the response of the logperch population and habitat quality to construction activities. PROJECT OBJECTIVES: Primary objectives are as follows: 1) estimate population density and distribution of Age-1+ Roanoke logperch in the RRFRP construction reach (CR) and in a reference reach (RR); 2) estimate population density and distribution of Age-0 logperch in CR and RR; 3) quantify and map the availability and distribution of habitat suitable for Age-1+ logperch in CR and RR; 4) quantify the availability and distribution of habitat suitable for Age-0 logperch in CR and RR; 5) describe the microhabitat use of logperch, 6) measure water quality in CR and RR; 7) explore logperch population dynamics; and, 8) describe detection-of-impact methods to be used in construction monitoring phases. PROGRESS: Impact calculations based on Age-1+ logperch population density indicated compliance of the RRFRP with its incidental take permit during 2010, the fifth year of construction-phase monitoring. Age-1+ logperch density in 2010 was similar to 2009 and lower than it had been in previous years, but was within previously-observed limits. Few Age-0 logperch were captured during electrofishing surveys, but visual surveyors recorded substantial numbers of Age-0 logperch. Differences between these two methods may be attributable to unmeasured environmental factors that reduced Age-0 fish abundance between the visual and electrofishing sampling periods. SuitableAge-1+ and Age-0 logperch habitats were present in amounts typical of other years. Underwater observations in fall provided new microhabitat-use data that could be used in the future to assess changes in habitat-use patterns as a result of the RRFRP, as well as to refine HSI models. Water quality was normal during the study period. Since the onset of construction in 2006, most measured variables have exhibited means and variances similar to those estimated during the pre-construction period, and few directional trendshave been observed. Age-1+ logperch density and habitat availability, water quality, Age-0 habitat availability, and patterns of microhabitat use have exhibited similar fluctuations in the construction and reference reaches, both before and after the onset of construction. Compliance with the RRFRP’s incidental take permit therefore has been maintained during the Phase-B period. The most concerning change between project phases, which coincides with the onset of construction, is the sustained trend of low estimated Age-0 logperch production over the Phase-B period. It is unknown whether this trough of recruitment is related to RRFRP activities, but the fact that low recruitment has been observed both in the construction and reference reaches suggests that it is not. Additional analyses were undertaken to explain interannual variation in logperch abundance using biotic and abiotic predictor variables. Length-frequency analysis of cohort production indicated that recruitment is cyclical, with strong cohorts occurring only infrequently. Regression tree models indicated that Age-0 abundance was negatively related to the magnitude of high streamflows during their first spring but positively related to the magnitude of low streamflows during the previous winter. Similarly, regression-tree models indicated that summer and fall Age-1+ logperch abundance was higher in years exhibiting lower, less variable spring streamflows but higher winter low flows. Spring flood patterns appear to be a key factor driving logperch population dynamics. However, flushing flows during winter may also be important for scouring sediment from feeding and spawning habitats.