Behavioral interactions between round gobies (Neogobius melanostomus) and mottled sculpins (Cottus bairdi)

We examined territorial behaviors and interactions between two species of benthic clingers, nonindigenous round gobies (Neogobius melanostomus) and relative mottled sculpins (Cottus bairdi). Interactions were observed for 24 h using infrared video photography in the laboratory. Trials were conducted using either a round goby or mottled sculpin resident in a shelter. An intruder (either a round goby or mottled sculpin) was added at random. Fish (fasted for 24 h before each trial) were used only once. Food (Gammarus, amphipods), maintained below satiation levels (estimated from functional feeding experiments), was used to enhance interactions, Over 24 h, amount of time spent in a refuge by a resident round goby did not change when intruders were present (round gobies or mottled sculpins). Time spent in a refuge over 24 h by a resident mottled sculpin was significantly reduced in the presence of a round goby intruder, but not in the presence of a mottled sculpin intruder. Both round gobies and mottled sculpins spent more time outside a refuge during the night than during the day. Resident round gobies and mottled sculpins spent more time in a refuge at night when a conspecific was present and even more time in the refuge when a fish of another species was introduced. The mean number of approaches, chases, and bites by resident round gobies was significantly greater than those of intruders. Mottled sculpin intruders never exhibited any aggressive behaviors (approaches, chases, bites). In cases where mottled sculpins were resident, a round goby intruder exhibited a greater number of acts (approaches, chases, bites) that were more aggressive compared to the resident sculpin (approaches). In nature, the aggressive habits of round gobies will likely result in the demise of mottled sculpins.