Swimming capacity and behaviour of juvenile round goby (Neogobius melanostomus)

The round goby (Neogobius melanostomus) is an example of an invasive species where the adults are unimpressive swimmers and yet via human activities, they have managed to rapidly invade the Laurentian Great Lakes, the Baltic Sea and many rivers in western Europe. The secondary spread from human-impacted sites has been attributed to adult life stages, despite their poor swimming capacity. However, the swimming capacity of early life stages of round goby has not been considered before. We therefore quantified critical swimming performance (U_crit), sprint swimming performance (U_sprint), burst swimming speeds, and swimming behaviours in newly emerged round goby fish that were between 10 - 25 mm in body length. The average U_crit, U_sprint, and burst speeds of these fish were an impressive 0.22 m/s, 0.34 m/s, and 0.67 m/s, respectively, with the capacity of these early stage juveniles ranging between 41-79% of what has been documented for adults. Notably, fish spent more time actively swimming as current speed increased, while station holding decreased. Taken together, our findings highlight that despite their small size, very young juvenile round goby are not simply passively moved by current and have movement capacities that approach that of the much larger adults. Our study emphasizes the need to consider the swimming capacity of all life stages as this information will better predict dispersal and range expansion and will help to design mitigation efforts to potentially prevent the spread of this and other invasive species.