Obstacles
Distinct from salmon and trout, the houting cannot jump or negotiate even small obstacles and will not use fish ladders.
This means that the fish often cannot reach large stretches of the watercourses because of impassable obstacles. Such obstacles are very common in Danish streams, and found at e.g. fish farms and hydroelectric power stations.
Straightening of the watercourses
Nearly all watercourses in Denmark have been straightened – a term that disguises the fact that the process involves deepening, widening and removing of stones, gravel and plants thereby transforming the watercourses into canals. This was done to enable the valleys to be cultivated.
Straightening of the watercourses often leads to unstable conditions and erosion of large amounts of earth and sand from the banks thereby impairing the living conditions for the plants and animals. Also, stone and gravel – i.e. the spawning grounds for the houting - is covered by sand, and the adhesive houting eggs have nothing left to stick to.
Pollution
Pollution among other things hinders the houting eggs development and they may suffocate.
Obstacles for the fry
Water intake at e.g. fish farms hinders the houting fry to freely swim out into the Wadden Sea – or they current may carry the fry into the fish ponds, where the farmed fish eats them.
Drainage
Drainage of meadows that otherwise would be flooded as well as the straightening of watercourses, means that the houting fry lack areas to remain for the first couple of months before they are able to withstand salt water. The fry are literally rushed into the salty sea too early – and dies.
Fishery
Even though the houting are a protected species, the fish are caught as by-catch by fishery - both recreational and professional.