Addition of structural complexity - contrasting effect on juvenile brown trout in a natural stream

• Published in: Ecology of freshwater fish 2015-10, Vol.24 (4), p.608-615
• Main Authors: Höjesjö, Johan, Gunve, Elin, Bohlin, Torgny, Johnsson, Jörgen I.
• Format: Article
• Language: English
• Subjects: biomass; brown trout; density; density dependent; Ecology; Ekologi; Fish; habitat complexity; Trout
• ISSN: 0906-6691; 1600-0633
• DOI: 10.1111/eff.12174

In a field experiment, we examined the effects of structural complexity in the form of added artificial plastic plants and shredded plastic bags on growth and abundance of juvenile brown trout (Salmo trutta). Just after emergence, the added complexity had a positive effect on the density, biomass and condition factor of young‐of‐the‐year (0+) brown trout. This difference in density was not present six weeks later. In contrast, both young‐of‐the‐year and older brown trout generally tended to be larger in the simple habitat. Hence, our data suggest that increased complexity initially is beneficial for young‐of‐the‐year individuals probably due to lower risk of predation and increased densities of prey. However, as density increases in the complex environment, it may induce negative density‐dependent effects, here reflected in smaller sized fish in the complex environment. This might force fish to redistribute to habitats with lower densities of conspecifics as they grow larger. We propose that habitat complexity can increase survival of yearlings in early phases and thereby also affect the overall population structure of brown trout in natural streams.