Influence of protected riparian areas on habitat structure and biodiversity in and at small lakes managed by recreational fisheries

Protected areas are a common management tool to conserve habitats and species by controlling access and disturbances by humans. Whenever protected areas result in restricting access to riparian zones in lakes, they may have positive effects on habitats and taxa beyond fish by lowering influences of trampling or boating on plants, by reducing the degree of human-induced disturbances to sensitive taxa such as birds, and by reducing fishing effort. However, especially in small freshwater systems knowledge about the functioning of protected areas that cover only parts of the lake shorelines is limited. We studied small gravel pit lakes in Germany where recreational fishing clubs have voluntarily assigned no-access riparian protected areas on parts of the lake shorelines and examined outcomes for habitat quality, plants, fish and bird populations. A total of 15 lakes were sampled, and we assessed habitat structure and abundance of plants, and fish within and outside protected areas and bird abundance at the lake scale, relying on standardized sampling methods. After controlling for confounding environmental factors related to lake morphology, age, nutrients, and land use, we detected positive contributions of small-scale riparian protected areas on habitat structure, riparian vegetation, local fish abundance and abundance of sensitive songbirds at the lake-scale, but we found no effects on aquatic vegetation and on disturbance-sensitive waterfowl species. Scale-restricted riparian protected areas voluntarily assigned by recreational fishing clubs can have positive outcomes for habitat quality and biodiversity, particularly by reducing trampling and access to anglers and other recreationists. Moreover, through provision of key habitat for young fish, small-scale riparian protected areas can also benefit fish abundance and in turn recreational fisheries.