Assessment of the conservation status of endemic sculpin Cottus haemusi (Cottidae) in the river Vit (Danube Tributary), northwest Bulgaria

Cottus haemusi (Marinov and Dikov, 1986. Acta Zool. Bulg. 3, 18–23) is an endemic fish species that is restricted to the upper tributaries of the river Vit, Northwest Bulgaria. After its discovery in 1986, no further investigation of the C. haemusi population has been conducted. The aims of the present study were to determine its current population status based on the distribution, abundance and size structure of the C. haemusi population and to analyse the main environmental parameters of its habitat. Five upland tributaries and the main river were examined in low-water periods in 2009 and 2010. Two-pass electrofishing surveys were performed at 14 sites to estimate species presence, abundance and size distribution. C. haemusi was only detected in two tributaries of the river Vit: Kostina and Toplja. The current investigation failed to find the species at previously recorded sites. The total distribution area of this species is estimated to be 16 200 m2. The observed abundance of the Vit sculpin ranged from 5.6 to 8.4 individuals·100 m–2, with a mean of 7.0 individuals·100 m–2. Investigation of the size structure revealed the relatively low contribution of one-summer-old individuals. Microhabitat preferences did not differ significantly from other European cottidae species. Only a higher percentage of cobbles distinguished sites with sculpins from those without. The restricted distribution and loss of the bullhead population from some localities in the river Vit could be explained by human disturbance and the deterioration of natural habitat. Several protection measures are discussed