Urban planning for fishes: untangling a new project’s effects from old infrastructure and regional patterns

Abstract

Urbanization has altered fish communities in many ways. However, as cities expand and redevelop, it is challenging to assess the impacts of new projects given existing alteration. We investigated how new and old infrastructure alters fish communities over a 4-year period in Metro Vancouver, British Columbia (Canada). We compared fish communities from a stream altered by a new rapid transit rail line and seven reference sites over 4 years, from before to after construction. We provide evidence that new and old projects depress the density, species richness, and diversity of fish communities. During and after construction, sections of the altered stream had one fewer species and lower density compared with preconstruction and reference streams. Streams without existing culverts had more species and greater diversity than those with culverts, but only in some years. Diversity was lower in 1 year of the study across all streams. We argue that most monitoring in Canada is insufficient to detect the incremental changes that new projects may cause and suggest improvements in monitoring and protecting reference streams.