Tests of artificial substrata as nursery habitat for young fish



Recruitment areas for freshwater fish are often negatively affected by eutrophication and physical disturbances. Vegetated areas, which are important nursery habitats, are reduced and water turbidity increased. As a method of compensation, we tested artificial substrata for young-of-the-year fish. The structures were made of spruce bundles, with and without surrounding nets, and placed in a hyper-eutrophic very turbid environment and in an undisturbed area with clear water. Both habitats were devoid of submerged vegetation. Young fish abundance in treated areas was compared with adjacent reference sites. In the clear water area, the abundance of all investigated species – perch, pike, bream, silver-bream and roach – was higher in areas with artificial refuges. A similar response was evident for cyprinids in the turbid environment. High abundance of pikeperch and ruffe appeared in the hyper-eutrophic test area. Neither of these species, nor perch, was attracted to the artificial refuges. The lack of response in perch and pikeperch suggests that the importance of structural refuge decreases in very turbid water for these species. Of the two methods tested, spruce bundles with surrounding nets generally attracted most young fish, implying that the nets further increased the refuge capacity by reducing predation risk. The conclusion is that artificial habitats could improve recruitment habitats and that protective devices can increase refuge capacity.