Bullhead and streams

The present-day character of the Krkonoše river system is closely related to the geomorphological evolution of the mountain range. With few exceptions, the directions of the major watercourses of the Krkonoše roughly follow the original valley basins of the Tertiary levelled topography.
According to the climate-hydrological classification of rivers, the Krkonoše rivers as well as all other Czech rivers belong to the so-called Central European (Oder) type, characterised by maximum flow rates in spring when the snow melts and minimum flow rates in summer when the evaporation is the greatest. Generally speaking, the Krkonoše are not a particularly significant water storage area. The low absorbing capacity of the Krkonoše rocks and mostly soft weathered rocks are offset by the relatively high precipitation rates and high forestation rates, but the small footprint of the mountain range and its catchment areas result in a high oscillation of flow rates in the rivers, manifested by dangerous floods during abundant rain periods and very low flow rates during longer dry periods.
The Krkonoše are the headwaters of the Czech Republic’s largest river, the Elbe, but it drains only about a third of the Czech side of the mountain range immediately. Still within the Krkonoše, it accepts the larger tributaries Bílé Labe (larger than the Elbe itself at the confluence) and the Dolský brook; it accepts other rivulets from the Krkonoše, the Malé Labe and the Čistá, only in the foothills, at Hostinné. The eastern third of the mountain range is drained by the Úpa, whose most important tributaries are the Zelený brook, Malá Úpa and Lysečinský brook. Waters from the western third of the mountain range flow into the Jizera, whose most important tributaries in the Krkonoše are the Mumlava, Rokytnický and Vejpálický brooks and the Krkonošská Jizerka.
Is the European bullhead really in trouble?
The European bullhead (Cottus gobio) is a relatively widespread species of the Czech Republic’s submontane watercourses, particularly those with a natural hydromorphology. The Red Book of the Czech Republic evaluates the fish species as near threatened (NT); it a specially protected species in the “endangered” category.
The tiny fish is one of the subjects of protection of the Krkonoše SCI. It lives in the sub-catchment areas of the Jizera, Elbe and Úpa. Its presence is currently confirmed in the Jizera, Jizerka, Rudník, Elbe, Vápenický brook, Malé Labe, Čistá, Malá Úpa and Úpa. The quantities of each sub-population differ, depending primarily on the condition of the habitat.
The habitat of the European bullhead is fast-flowing, well-oxygenated watercourses with sufficient hiding capacity. The bullhead does not have a swim bladder, so it only moves by dashing at the bottom, where it seeks for hiding under larger stones and boulders, or in the root systems of littoral trees or aquatic macrophyta stands. The bullheads reproduce earlier than other fish species in streams, mostly in March, when the females lay eggs under stones; the males then take care of the eggs. The bullheads are mainly threatened by impaired water quality as well as changes to stream hydromorphology affecting flow and reducing hiding capacity, changes in hydrological conditions. The species protection therefore consists chiefly in protecting the watercourse habitat.
A constant and unresolved problem is modifications to watercourses in the form of insensitive canalisation and development of migration barriers, which significantly restrict the growth of populations of aquatic and water-bound organisms. That is why the project will focus on passability and revitalisation of parts of watercourses selected in the preparatory stage.
Problems that are currently evolving include artificial snowing in sports resorts and the connected effects on the flow rates in winter (in the Elbe catchment area in particular). Another long-term problem is the exploitation of the energy potential of surface waters for electricity generation in small hydropower plants The gradually improving water chemistry (e.g., in the Jizera catchment area) permits return of original species to their former sites.
The Krkonoše SCI is inhabited by several thousand individuals.
According to incomplete information, the population status in the Krkonoše SCI is stable in some areas, particularly at the edges of the area and in project areas (e.g., in small hydropower plant bypasses), but it is vulnerable. The species has a significant potential for population improvement.