Table 3 Sampling sites and number of specimens in the morphometric study.

1

Stream Broel between Broel and Winterscheidt, North Rhine-Westphalia, Germany; 50°47'N 7°20'E

48

48 Stream Broel sculpins

2

Stream Broel south of Broel, North Rhine-Westphalia, Germany; 50°47'N 7°19'E

48

42 Stream Broel sculpins; 1 BI Hybrid

3

Stream Broel at Mueschmuehle, 200 m above outlet into River Sieg, North Rhine-Westphalia, Germany; 50°47'N 7°18'E

130

26 Stream Broel Sculpins; 45 BI Hybrids; 13 Invasive Sculpins

4

River Sieg at Allner, below outlet of Stream Bröl, North Rhine-Westphalia, Germany; 50°46'N 7°18'E

36

2 Stream Broel Sculpins; 16 BI Hybrids; 2 Invasive Sculpin

5

Stream Wahnbach, Outlet into River Sieg at Seligenthal, North Rhine-Westphalia, Germany; 50°47'N 7°16'E

4

1 Invasive sculpin

6

Stream Pleis, outlet into the River Sieg at Niederpleis, North Rhine-Westphalia, Germany; 50°46'N 7°12'E

5

5 Invasive sculpin

7

River Sieg at Muehlenbach, North Rhine-Westphalia, Germany; 50°47'N 7°10'E

35

19 Invasive sculpin

8

Stream Naaf, Outlet into River Agger, North Rhine-Westphalia, Germany; 50°51'N 7°14'E

48

1 Stream Naaf sculpins;

9

Stream Naaf at Kreuznaaf, 200 m above outlet into River Agger, North Rhine-Westphalia, Germany; 50°51'N 7°14'E

48

30 Stream Naaf sculpins

10

Stream Naaf southeast of Hausdorp, North Rhine-Westphalia, Germany; 50°52'N 7°16'E

48

45 Stream Naaf sculpins