First description of redds of the only non‐introgressed population of a critically endangered salmonid in a stream vulnerable to droughts

Abstract

AbstractLocation, dimensions, substrate and depth of the redds of the only non‐introgressed population of the critically endangered Mediterranean trout Salmo cettii Rafinesque 1810 were investigated over 2 days, in January–February 2021, in a reach located in the headwaters of Tellesimo stream, Sicily. The habitat type (pool, riffle and glide) was identified for all the 13 redds observed; lengths, widths, depths and substrate size were measured in a sample of them. Eighty‐five percent of the redds were located in pools and 15% in glides; no redd was found in riffles. The median total redd length was 80 cm (range: 43–580 cm; n = 11), and the median total area was 0.20 m2 (range: 0.01–2.09 m2; n = 11). The median size of dominant substrate in pot was 0.65 cm (range: 0.20–2 cm) and in tailspill 1.25 cm (range: 0.50–2.00 cm). Redds were found at median water depth of 27.5 cm (range: 12–98 cm). These results represent the first description of the characteristics of the spawning nests of this autochthonous salmonid.