Fig 1.
Study area at the upper Danube River between Austria and Germany.
Study area with four representatively chosen rip-rap sampling stretches covering a recent round goby invasion along the headwater reaches of the upper Danube River in Bavaria, southern Germany. The consecutive numbers in grey rectangles denote two pioneering and two longer established (sub-)populations: a newly colonizing (sub-)population at a recent “invasion front 2014” (sampling stretch #4, first record: August 2014), a former “invasion front 2010” (sampling stretch #3, first record: September 2010) and two established sub-populations from an “established area” (sampling stretches #1 and #2, first record before 2007). The Danube basin and the location of the study area within the drainage area are highlighted. Filled black circles denote important cities along the Danube River.
Table 1.
Sampling design and location of river stretches.
Fig 2.
Total length of adult round gobies and the most frequent native fish species in 2010, 2011 and 2015 at four sampling stretches along the upper Danube River.
Total length (LT in mm) of a) adult invasive alien round gobies (LT > 5 cm) and b) native barbel and chub at four sub-populations from the established (first record before 2007; stretches #1 and #2) and pioneering area (invasion front 2010 (stretch #3) and the invasion front 2014 (stretch #4)) in the upper Danube River, Bavaria southern Germany.
Table 2.
Population dynamics in N. melanostomus and bycatch at three areas (stages) of the invasion.
Table 3.
Comparison of performance indicators of N. melanostomus at population level (sampling 2015).
Table 4.
Comparison of performance indicators of N. melanostomus at specimen level.
Fig 3.
Nonmetric multidimensional scaling of N. melanostomus performance metrics.
Nonmetric multidimensional scaling (NMDS) of N. melanostomus population-specific performance metrics calculated from point-abundance sampling data (autumn 2010, 2011 and 2015) in the upper Danube River, Bavaria, southern Germany. Dissimilarity-distances between 14 samples from four river stretches were calculated using the squared euclidian distance and displayed in green (“established area” with stretches #1 and #2), yellow (“invasion front 2010”, stretch #3) and red spots (“invasion front 2014”, stretch #4). The spot labels are encoded with sampling stretch number, river side (r = right, l = left) and year of sampling. LT(f), LT (m), LT(j), MT(f), MT(m), MT(j), K(f), K(m), K(j), proportion of females and catch data (mean CPUE and frequency of occurrence of (i) N. melanostomus, (ii) Barbus barbus and Squalius cephalus (combined) and (iii) other fish species) from the corresponding sampling sites were used as variables (stress = 0.05).
Table 5.
Comparison of N. melanostomus first record data.
Fig 4.
Spatio-temporal invasion performance: Neogobius melanostomus along the upper Danube River.
Spatio-temporal performance of four Neogobius melanostomus (sub-)populations (stretches #1 to #4) in the upper Danube River displayed by length-frequency histograms (white bars = juveniles, grey bar = females, black bars = males). Fish data are based on point abundance sampling of electrofishing in autumn 2015 in the upper Danube River, Bavaria, southern Germany. The time since invasion in years is displayed within each panel in brackets and means the difference between sampling time and first record.
Fig 5.
Five years of invasion–Temporal population dynamics of Neogobius melanostomus at the invasion front 2010.
Five years of invasion at the invasion front 2010 (IF2010): Length-frequency-histograms displaying the temporal dynamics of the N. melanostomus population at stretch #3 from first record (introduction, 2010) to first appearance of juveniles, i.e. successful reproduction (establishment, 2011) until mass development (spread, 2015) with white bars = juveniles, grey bar = females, black bars = males. Fish data are based on point abundance sampling of electrofishing in autumn 2010, 2011 and 2015 in the upper Danube River, Bavaria, southern Germany.