Effects of environmental variation on stocking success of an endemic black bass species in the Chattahoochee River, Georgia

Abstract

In 2003, the Georgia Department of Natural Resources and the National Park Service initiated a five-year shoal bass stocking program below Morgan Falls Dam in the Chattahoochee River, Georgia with a goal of rehabilitating population abundance to historic levels and to provide further sport-fishing opportunities. Shoal bass were marked with oxytetracyline (OTC) and stocked as juveniles at one of two size classes (Phase I [~25 mm, TL] and Phase II [~60 mm, TL]) in spring (April - June) each year (2003-2007). Contribution to the adult population was evaluated by collecting adult shoal bass with boat electrofishing from 2007-2011 and viewing their otoliths for the presence of an OTC mark. Stocked shoal bass dominated the total sample of adult fish collected (62%) and most of these fish (41%) were stocked at the larger size class. Based on results from multiple regression modeling, age-3 shoal bass catch-per-unit-effort was positively related to mean size at stocking and spring water temperatures. Natural mortality of shoal bass in this population was low (20%) with increased longevity (14 years) and low growth rates. After stocking, juvenile shoal bass growth was greatly reduced, which was visible on the otolith as a constricted daily growth increment. Daily rings subsequent to the natural mark were constricted and difficult to discern resulting in underestimated ages depending on stocking location. Shoal bass and largemouth bass tended to be older and grow faster at warmer, more downstream sites. Overall, the five-year shoal bass stocking program was successful in increasing shoal bass abundance in the Chattahoochee River below Morgan Falls Dam, but demonstrates the effects of an unnaturally cold environment on warmwater fish species.