American Fisheries Society Symposium 87: 2019 Repatriation of Guadalupe Bass in the Blanco River, Texas: A Case Study in the Opportunistic Use of Drought as a Fisheries Management Tool STEPHAN MAGNELIA*, GORDON LINAM, RYAN MCGILLICUDDY, KEN SAUNDERS, AND MELISSA PARKER Texas Parks and Wildlife Department Post Office Box 1685, San Marcos, Texas 78667, USA TIMOTHY BIRDSONG Texas Parks and Wildlife Department 4200 Smith School Road, Austin, Texas 78744, USA DIJAR LUTZ-CARRILLO, JÁNAYE WILLIAMSON Texas Parks and Wildlife Department 505 Staples Road, San Marcos, Texas 78666, USA RACHAEL LINDSEY RANFT1 The Nature Conservancy 23345 Bat Cave Road, San Antonio, Texas, 78266, USA TIMOTHY BONNER Texas State University, Department of Biology/Aquatic Station 601 University Drive, San Marcos, Texas 78666, USA *Corresponding author: [email protected] 1Current address: Eco-vative Associates 223 Paisano Drive, Victoria, TX 77904, USA 1 2 Magnelia et al. Abstract.—Repatriation of Guadalupe Bass Micropterus treculii was un- dertaken in the Blanco River, Texas, after extirpation due to hybridization with non-native, introduced Smallmouth Bass Micropterus dolomieu. In summer 2011, much of the river was reduced to a series of disconnect- ed, enduring pools due to severe drought. Electrofishing and seines were used to remove Smallmouth Bass from fifty-two enduring pools in a 24-km reach of the river upstream of a natural fish passage barrier. After the removal effort was completed, stockings of non-introgressed, hatchery- produced Guadalupe Bass fingerlings (n = 316,016) were initiated in spring 2012 when river flows returned. Successful recruitment of wild, naturally-produced Guadalupe Bass was documented in fall 2014 and 2015. In the reach where Smallmouth Bass were removed, only Guada- lupe Bass were detected, despite a historic flood event in spring 2015, which provided an opportunity for upstream movement of Smallmouth Bass and Guadalupe Bass x Smallmouth Bass hybrids past the barrier. Introduction a result of hypolimnetic dam releases (Ed- wards 1978) and hybridization with SMB Guadalupe Bass (GB), the official state (Littrell et al. 2007; Bean et al. 2013). Since fish of Texas, is endemic to streams that 1990, Texas Parks and Wildlife Department originate in the Edwards Plateau ecoregion (TPWD) restoration efforts have included a of central Texas, including portions of the genetic refuge restoration strategy (Araguas Brazos, Colorado, Guadalupe and San Anto- et al. 2008, 2009; Caudron et al. 2011), where nio river basins (Figure 1; Curtis et al. 2015). SMB are not stocked in any location that pro- They inhabit spring-fed streams, with larger vides it access to GB populations whose ge- individuals associated with moderate depths netic purity is to be maintained or restored (1.0 m) and slow current velocities (<0.05 (Garrett 1991). Despite this effort, the pro- m/s) downstream from riffles with instream portion of SMB and GB × SMB hybrids (hy- cover such as log complexes, boulders, and brids) within some streams has been shown undercut banks (Edwards 1980; Perkin et al. to continually increase until Guadalupe Bass 2010; Curtis et al. 2015). Juveniles initially are extirpated (Littrell et al. 2007; Bean et al. seek swift habitats, but transition to deeper 2013; Fleming et al. 2015). In response to the depths and moderately flowing eddies as they threat of additional extirpations of GB popu- near age-1 (Edwards 1980; Curtis et al. 2015). lations, TPWD initiated the Guadalupe Bass They are a highly sought after sport fish for Restoration Initiative (GBRI) (Birdsong et al. river anglers (Thomas et al. 2015) and also a 2010; Garrett et al. 2015) in 2010. species of conservation concern (Hubbs et al. The Blanco River is located along the 2008; Texas Parks and Wildlife Department eastern edge of the Edwards Plateau ecore- 2012) due to decreased stream flow (Hurst gion in south-central Texas in an area com- et al. 1975), reservoir construction (Edwards monly referred to as the Texas Hill Country. 1978), habitat degradation, and hybridiza- The watershed (Figure 1) is within the his- tion with nonnative Smallmouth Bass (SMB) torical range of GB and is of high ecological (Edwards 1980). Extirpation of GB has oc- importance given that it hosts 36 species of curred in portions of their historical range as conservation concern including five species Repatriation of Guadalupe Bass in Texas: Drought as a Fisheries Management Tool 3 Figure 1. Distribution of Guadalupe Bass including historical and introduced populations. Map adapted from Curtis et al. 2015. of fish (TPWD 2012). The watershed is also a initiated in the Guadalupe River headwaters priority for conservation investments by The in 1992 intended to reduce hybridization and Nature Conservancy (TNC) who has estab- genetic introgression of wild populations of lished relationships with a network of land- GB (Fleming et al. 2015); however, because owners interested in wildlife conservation of state fish hatchery production resource (TNC 2016). Furthermore, the Blanco River constraints, supplemental stocking of GB in is at high risk for habitat alteration due to its the Blanco River was abandoned after 1995 location just west of the Austin-San Antonio (G. Garrett, TPWD retired, personal com- urban corridor (Crawford et al. 2016). These munication), and the apparent extirpation of factors would have otherwise propelled the GB from the Blanco River was subsequently Blanco River to be considered as a priority documented in 2005 (Littrell et al. 2007). for the GBRI; however, stockings of SMB in The continued persistence of SMB and the Blanco River in 1977 and 1980 resulted in hybrids in the Blanco River following GB GB × SMB hybridization and genetic intro- extirpation provided evidence of the suit- gression (Garrett 1991). By 1991, 30% of the ability of stream habitats to support SMB in micropterids collected from the Blanco River the long-term. Bean et al. (2013) observed were genetically identified as GB × SMB variable levels of GB x SMB hybridization hybrids (Morizot et al. 1991). Supplemental in streams where nonnative SMB had been stockings of 80,014 genetically pure GB fin- introduced, with the highest levels of hybrid- gerlings occurred in the Blanco River in 1994 ization found in streams where SMB persist- and 1995, a conservation strategy that was ed long-term. Fisheries managers believed 4 Magnelia et al. that supplemental stockings of GB, such as forts might be effective. The objective of this those made in the Guadalupe River (Fleming project was to implement an isolation man- et al. 2015), would likely be an ineffective agement strategy (Novinger and Rahel 2003) repatriation approach in the Blanco River in and establish a self-sustaining population of the absence of SMB removal. Furthermore, pure GB upstream of the barrier, through re- a large-scale removal program for SMB and moval of SMB and hybrids, and repatriation hybrids did not seem feasible, so efforts to re- of GB through stocking. patriate GB to the Blanco River were deemed futile. Repatriation Area Description This perspective changed in 2011, a time during which most of Texas experienced The Blanco River is intermittently fed exceptional drought conditions (National by shallow springs and seeps, and in some Drought Mitigation Center et al. 2016). Re- reaches the channel gains water, while in cord high temperatures from June through others water is lost to the aquifer through August combined with minimal precipita- the karst landscape (Slade et al. 2002; Wier- tion contributed to record low stream flows man et al. 2010). Although streamflow was throughout much of the State (Winters 2013). absent during the summer of 2011, these The Blanco River was reduced to a series of springs as well as approximately 90 low- disconnected enduring pools. Conditions ap- head dams and low-water crossings influ- peared to offer an opportunity for the targeted enced the amount of water (i.e., number of removal of SMB and hybrids seeking refuge enduring pools and depth of those pools) that in those pools. Opportunistic removal of in- remained. While the entirety of the Blanco vasive fish species that aggregate as a result River and its tributaries were considered of weather conditions has been suggested for the repatriation effort, for planning pur- as an effective population control strategy poses the river was divided into four distinct (Shepard et al. 2014; Koizumi et al. 2017). reaches (Figure 2). A limitation of this strategy for the Blanco Reach 1 was the upper 38 km of the River was a constant source of SMB and hy- mainstem Blanco River and tributaries from brids known to persist within the San Marcos the headwaters to a low-head dam just down- River, a spring-fed river that had stable flows stream from the city of Blanco (Figure 2). throughout the 2011 drought. The Blanco This reach was highly fragmented with 37 River is a tributary of the San Marcos River low-head dams and 17 low-water crossings. (Figure 1), and in the absence of an effective It also contained 36 main channel small im- barrier to upstream fish movement, we be- poundments, many of which still held large lieved that SMB and hybrids would eventu- areas of water during summer 2011. The low- ally move upstream and recolonize upon the er 6 km of this reach entering and in the city return of normal flows. However, data from of Blanco was characterized by a series of past fish collections revealed a discontinuity 10 consecutive impoundments. While some in the Blanco River fish assemblage upstream of these were dry others had as much as 2–3 from a gorge containing a series of waterfalls ha of water remaining (Figure 2). The lower (Texas Game and Fish Commission 1957; portion of this reach is reported to be a gain- Bean et al. 2007). It was thought this natu- ing reach (Wierman et al.