Natural shorelines support greater diversity and abundances of fishes than armoured shores along Chicago's waterways

Abstract

Abstract Shoreline armouring is one of the most ubiquitous alterations to aquatic systems globally. Armouring and hardening to prevent erosion and maintain land uses reduce or eliminate habitat complexity that softer and more natural, vegetated shorelines offer. The effects that shoreline armouring has had on biodiversity of coastal and estuarine communities are well studied, while studies in freshwater systems remain sparse. Data collected during a large‐scale long‐term fish survey with high spatial resolution from the Invasive Carp Regional Coordinating Committee's Monitoring and Response Work Group were re‐analysed to assess the effects that bulkhead versus natural shorelines have on fish diversity and abundance. Lengths of bulkhead, natural and riprap shoreline were calculated within 300 m of each sampling location, which occur every 100 m throughout the Chicago Area Waterway System. Water depths of each sampling location were also classified into deep (>6 m), mid‐range (4–6 m) or shallow (<4 m) to account for potential variations in gear efficiencies. Fish species richness and abundance increased with increasing proportions of natural shoreline, which can be contrasted with stronger (i.e., steeper slope) decreases as proportions of bulkhead shorelines increased. The results show strong evidence for the negative effects of shoreline armouring of freshwater ecosystems and are consistent with those shown in coastal ecosystems studies. As cities continue to encroach on freshwater systems, greater emphasis on maintaining natural riparian shorelines and ecoengineering hardscapes will increasingly be important for freshwater conservation.