Round goby predation on smallmouth bass offspring in nests during simulated catch-and-release angling

Round goby Neogobius melanostomus first appeared in Lake Erie in 1993 and now occur in extremely high densities in some areas. As known nest predators, round goby currently pose a threat to nest-guarding smallmouth bass Micropterus dolomieu. We conducted manipulative experiments to evaluate the combined effects of round goby predation and catch-and-release angling during 1999-2001 in the Bass Islands, Lake Erie. We quantified how many smallmouth bass Offspring were consumed by round goby when nest-guarding smallmouth bass males were present, removed, and recovering from angling-related stress. In 10 h of video observations, we only saw one instance of round goby consuming smallmouth bass offspring while the nest was guarded. Upon removal of nest-guarding smallmouth bass, round goby quickly entered unguarded nests (4.3 round goby/min for nests with unhatched embryos and 1.8 round goby/min for nests with hatched embryos). During experimental catch-and-release angling, round goby consumed an average of 2,000 unhatched embryos before the guardian male returned, but postreturn offspring losses were minimal while the male recovered from angling stress. For an average smallmouth bass nest in the Bass Islands, round goby could consume all offspring from an unguarded nest in about 15 min. Round goby predation and smallmouth bass angling combined to reduce survival of smallmouth bass embryos, but we did not observe round goby consuming free-swimming larvae or juveniles. If the number of surviving smallmouth bass embryos drives adult population size, managers should consider angling regulations that reduce interference with nesting males, thus limiting the deleterious effects of round goby.