Supplementary Material 1 Mean ± SE fish density (number/100m2) estimates based on 3-pass snorkel surveys conducted at each of the 24 sampling sites.

Site name / Site numbera / Coordinates / Fish species / Dispersal barrierc
Latitude / Longitude / Redfin / Kurper / Galaxias / Trout
Amandel / 1 / 33˚44.197' S / 19˚06.820' E / 7.43 ± 0.61 / 0.51 ± 0.00 / 0.68 ± 0.34 / - / -
Bobbejaans / 2 / 33˚25.783' S / 19˚17.000' E / 13.30 ± 0.28 / - / - / - / -
Buffelshoek / 3 / 33˚27.514' S / 19˚36.813' E / 16.51 ± 2.43 / 6.11 ± 2.95 / - / 2.45 ± 0.40 / -
Du Toits / 4 / 33˚43.485' S / 19˚06.747' E / 72.29 ± 24.52 / - / - / - / we
Groothoek / 5 / 33˚43.028' S / 19˚09.667' E / - / - / - / 102.32 ± 7.36 / -
Hartmanskloof / 6 / 33˚24.525' S / 19˚27.172' E / - / - / - / 7.85 ± 3.72 / -
Houtboskloof / 7 / 34˚00.412' S / 19˚13.322' E / - / - / - / 40.79 ± 5.90 / -
Jan du Toit / 8 / 33˚25.647' S / 19˚39.774' E / 1.36 ± 0.34 / 0.51 ± 0.29 / - / 0.85 ± 0.17 / -
Kaaimansgat / 9 / 33˚25.103' S / 19˚27.160' E / - / - / 2.46 ± 0.63 / 0.72 ± 0.14 / -
Klip / 10 / 33˚52.138' S / 19˚20.819' E / - / - / - / 61.71 ± 5.13 / -
Kraalstroom / 11 / 33˚46.243' S / 19˚09.199' E / - / - / - / 21.51 ± 1.62 / -
Krom / 12 / 33˚46.124' S / 19˚08.955' E / 0.84 ± 0.17 / - / - / 1.01 ± 0.00 / -
Molenaars trib.b / 13 / 33˚41.618' S / 19˚11.300' E / - / - / - / 3.51 ± 0.40 / -
Morainekloof / 14 / 33˚43.478' S / 19˚06.746' E / 2.25 ± 0.16 / 0.80 ± 0.16 / - / 1.93 ± 0.00 / -
Raaswater / 15 / 33˚58.791' S / 19˚16.743' E / - / - / - / 1.30 ± 0.00 / -
Sandspruit / 16 / 33˚42.987' S / 19˚09.683' E / 23.79 ± 5.15 / 11.32 ± 2.77 / 82.69 ± 20.85 / - / we
Stettyn / 17 / 33˚56.374' S / 19˚10.129' E / 0.41 ± 0.20 / - / 51.93 ± 3.49 / - / db
Tierhok / 18 / 33˚48.702' S / 19˚18.917' E / 196.71 ± 29.10 / - / - / - / wa
Tierkloof / 19 / 33˚29.151' S / 19˚31.755' E / 21.51 ± 2.03 / 6.09 ± 3.06 / - / - / db
Tierstel / 20 / 33˚56.362' S / 19˚10.112' E / 103.00 ± 6.87 / 12.63 ± 0.83 / 0.66 ± 0.17 / - / wa
Titus trib.b / 21 / 33˚55.210' S / 19˚19.758' E / 16.49 ± 2.36 / 19.59 ± 2.29 / - / - / we
Waaihoek / 22 / 33˚50.215' S / 19˚15.483' E / 9.65 ± 0.79 / - / 6.83 ± 1.04 / - / wa
Wolwekloof / 23 / 33˚24.738' S / 19˚29.885' E / 136.08 ± 18.88 / 6.69 ± 0.30 / 0.17 ± 0.17 / - / -
Wolwenberg / 24 / 33˚25.323' S / 19˚26.633' E / 92.36 ± 6.94 / 8.77 ± 1.55 / - / - / wa

a Site numbers correspond to the numbers in Fig. 1

b Unofficial site name

c “we” = weir, “wa” = waterfall, “db” = dry/braided reach