Downstream drift of round goby (Neogobius melanostomus) and tubenose goby (Proterorhinus semilunaris) in their non‐native area

Abstract

Several Ponto‐Caspian gobiid species have recently expanded their ranges in Europe and North America. This is the first study to demonstrate passive downstream dispersal (drift) of the round goby (Neogobius melanostomus) and tubenose goby (Proterorhinus semilunaris) in newly colonised areas (River Dyje, Danube basin), a factor that could play an important role in their dispersal. Drift duration (i.e. number of dates on which the species was caught) in round goby was longer than that of both native species and tubenose goby, providing a possible advantage. Size of drifting fish was restricted to a narrow range of 6–8 mm and 5–8 mm for round and tubenose goby, respectively. Drift in both species occurred almost completely during hours of darkness (<1 lux) and fish size did not vary throughout the night. In both species, drift density increased significantly during the first hour after dusk. Round goby density gradually decreased up to dawn, while tubenose goby density varied throughout the night with no clear pattern. Drift of early life stages appears to be an important phenomenon that has not received adequate attention in studies of round and tubenose goby ecology and dispersal.

The drift of early life stages of Percidae and Gobiidae (Pisces: Teleostei) in a free-flowing section of the Austrian Danube

“…This assumption, however, may be too simplified. The increase in DD after dusk is well supported from previous studies (Pavlov et al, 1978;Brown & Armstrong, 1985;Zitek et al, 2004a;Janáč et al, 2013). It appears though that the onset und duration of drift activities during the night is variable and is likely dependent on local factors such as turbidity and others (Pavlov, 1994).…”

“…Note that the total number of individuals is lower than in Table 3, because size measurement was not possible for all specimens Hydrobiologia (2016) 781:199-216 209 This may lead to an advantage of gobiids over most native fishes which inhabit similar habitats and could be one explanation for their high invasive success. Janáč et al (2013) found a similar multimodal and prolonged seasonal pattern of Neogobius in the River Dyje (Czech Republic, Danube Basin), although with a later onset of drift activity. The seasonality of drift intensity found in Proterorhinus matches only partially with other studies.…”

“…In a study in an artificial sidearm of the Austrian Danube, Proterorhinus was the dominant genus and exhibited a slightly bimodal seasonal pattern, with high DD throughout June and very low values in late May and early August (Zitek et al, 2004a). In contrast, Janáč et al (2013) found maximum DD in May and almost no specimens of Proterorhinus after mid-June in the Dyje. Drifting in Proterorhinus seems therefore variable, and continuous spawning may not always occur.…”

“…It is likely that the gobiids were spawning continuously throughout the sampling period, because both mean and minimum sizes of Proterorhinus and Neogobius remained constant throughout May and June and recently hatched individuals were found even at the last sampling days. A prolonged spawning period from approximately April to September is thought to occur for these species (Miller, 2004;Janáč et al, 2013). Note that the total number of individuals is lower than in Table 3, because size measurement was not possible for all specimens Hydrobiologia (2016) 781:199-216 209 This may lead to an advantage of gobiids over most native fishes which inhabit similar habitats and could be one explanation for their high invasive success.…”

“…However, DD varied during the day and maximum values were found at (gobiids), or shortly after (percids), midnight. Janáč et al (2013), who have monitored drift patterns in the River Dyje from sunset to sunrise, found differences in the nocturnal drift patterns between N. melanostomus and P. semilunaris. While the abundance of the former rapidly decreased after a peak 2.5 h after dusk, numbers of the latter varied until dawn.…”