Invasion strategy and abiotic activity triggers for non-native gobiids of the River Rhine

Abstract

The 24 hour activity patterns of three non-native gobiids (round goby Neogobius melanostomus, Western tubenose goby Proterorhinus semilunaris and bighead goby Ponticola kessleri) were assessed over 46 consecutive months between 2011 and 2014 from their occurrence in the cooling water intake of a nuclear power plant on the River Rhine, Germany. In total, 117717 gobiids were identified and classified. The occurrence of all three species varied strongly between sampling years, and species-specific activity triggers were identified. The activity of juveniles of all three gobiids species was positively temperature dependent while adult tubenose goby activity appeared to be negatively temperature dependent. Increasing fluvial discharge in the adjoining main river stimulated the activity of juvenile round goby but inhibited activity of adult tubenose goby. Except for adult bighead goby, activity was also structured by time of day, but with no uniform mean. Meteorological factors such as precipitation, air pressure and duration of sunshine hours had little or no influence on gobiid activity. On selected rare occasions, mainly at night, all three species exhibited pulsed swarming behaviour, with thousands of individuals recorded in the intake water. Round goby swarms exhibited both the highest intensity and the largest swarming individuals, suggesting a potential competitive advantage over tubenose and bighead goby. Electric fishing surveys in natural river stretches corroborated this observation. Negative effects on the native fish fauna were apparent only for the bullhead, Cottus gobio.The activity triggers identified offer a unique insight into the invasion mechanisms of these ecosystem-changing non-native gobiids.

Abiotic triggers for sea and river lamprey spawning migration and juvenile outmigration in the River Rhine, Germany

“…Weibel). Long-running electric fishing surveys in this part of the river have recorded large numbers of non-native gobiids in recent years (between 2008 and 2015) (Baer et al, 2017), but not one single adult lamprey. In the present study, PMf individuals were only recorded between March and May.…”

“…Abstracted cooling water is regarded as coming from the mainstreaming water body of the Rhine (Baer et al, 2017), although it is actually taken from an artificial lake connected with the river, with the intake located some 300 m from the main channel. Abstracted cooling water is regarded as coming from the mainstreaming water body of the Rhine (Baer et al, 2017), although it is actually taken from an artificial lake connected with the river, with the intake located some 300 m from the main channel.…”

“…The study area, the structure of the cooling water intake and the sampling mechamism are explained in detail in an earlier paper (Baer et al, 2017). The following outline contains information essential for understanding the procedure in general terms.…”

“…The main channel of the Rhine adjacent to the NPPP is approximately 220 m wide, with an average depth of 3.75 m and a yearly average discharge of 1,265 m³/s. Abstracted cooling water is regarded as coming from the mainstreaming water body of the Rhine (Baer et al, 2017), although it is actually taken from an artificial lake connected with the river, with the intake located some 300 m from the main channel. Water is drawn from the full water depth of the lake and transported through different barracks, at the end of which fishes, crustaceans, plant material and debris are removed by 12 vertical screens with a square mesh size of 1 mm.…”

“…In total, about 6.5 million fish were collected (Baer et al, 2017). Of 46 identified fish taxa, 33 are considered autochthonous, constituting 84.6% of the natural fish fauna of the Rhine (n = 39), while 13 are allochthonous (Baer et al, 2014).…”