Radio‐tagged, hatchery‐reared guide fish: a method for uncovering information about rare or cryptic fishes

The behaviour and habitat selection of many fish species render them cryptic, difficult to observe, capture or study, and ultimately, poorly known (Bruton 1995). The cryptic nature of such species leads to uncertainty as to the status of local populations or even whether a population is present within a system. This uncertainty imposes difficult challenges on resource management agencies tasked with managing such species in the face of continued anthropogenic alteration and destruction of aquatic habitats (Bruton 1995; McKinney 1999). Often, data on which to base management or conservation efforts or to determine critical habitat for protection are non-existent, and generating these data can be expensive and time consuming. Occasional serendipitous discoveries can help inform this process, but this approach is unreliable. Robust redhorse, Moxostoma robustum (Cope), offers an excellent example of the difficulties uncertainty imposes on conservation of cryptic species. Robust redhorse is a large catostomid native to medium to large rivers along the south Atlantic coast but is currently known only from three drainages in North Carolina, South Carolina and Georgia (Cooke, Bunt, Hamilton, Jennings, Pearson, Cooperman & Markle 2005). Stocked populations have been established both in additional drainages and in other portions of the Altamaha and Savannah. This species was first described by Cope (1869), but the description and the fish were lost to science for 121 years until the fish was rediscovered in the Oconee River in central Georgia in 1991 (Ruetz & Jennings 2000; Cooke et al. 2005). Robust redhorse probably went unnoticed for such a long time because of a combination of habitat selection (viz. robust redhorse occupying difficult-tosample riverine habitats; Grabowski & Isely 2006), restricted range because of dam construction, population decline and a historic neglect on the part of fisheries agencies towards non-game species such as suckers (Cooke et al. 2005). Robust redhorse spends most of its time in deep (>2 m) water in association with large woody debris along the outer edge of riverbends (Grabowski & Isely 2006). This habitat is difficult to sample effectively with standard methods such as electric fishing (Bayley & Austen 2002). As a result, early efforts to determine the status of this species in its historic range were hampered, and new data about the species habitat use and distribution were acquired with the occasional capture of one or two individuals (DeMeo 1997, 1998, 1999, 2000, 2001). Radio-telemetry of wild individuals played a major role in assessing the movement patterns and habitat use of known populations of robust redhorse in the Savannah River (Grabowski & Isely 2006) and the Pee Dee River (R.J. Heise, personal communication). Further, telemetry has been instrumental in locating previously unknown populations by successfully directing sampling efforts to locations occupied by this species and allowing for the identification of spawning aggregations. In this paper, the use of radio-tagged hatchery-reared guide fish to direct sampling efforts to capture resident fish and to identify