Historical changes in the fish communities of the Credit River watershed

Abstract

Watersheds in southern Ontario are of high conservation concern due to their diverse fish communities, productive environments, and threats from numerous anthropogenic stressors. The Credit River watershed, located west of the Greater Toronto Area, has over 60 fish species, and multiple stressors including urbanization, climate change, and aquatic invasive species. This study examines fish community change in the Credit River watershed. Historical fish datasets collected in the watershed from 1954 to 2015 were analyzed to examine richness patterns, temporal trends in species distributions, and faunal similarity at the site and sub-watershed levels. Species richness increased over time at the site and sub-watershed level, displaying predictable richness patterns due to anthropogenic introductions and changes in sampling methods. Species distribution patterns remained largely stable over time with decreases in some species (e.g. Redside Dace) and increases in others (e.g. Largemouth Bass). Faunal similarity also increased over time at the site and sub-watershed level, indicating that the fish communities in the Credit River are homogenizing.

Keywords:

• conservation
• richness
• homogenization
• stressors

Acknowledgements

We would like to thank: Henry Regier for his insight into the 1954 sampling methods; Credit Valley Conservation, and Jon Clayton, Phil Bird, and Deborah Martin-Downs in particular, for providing historical fish datasets used in this report and for their continued guidance on this project; and the Mandrak Lab at the University of Toronto Scarborough for their help throughout this project. The NSERC CREATE Great Lakes program provided funding.

Supplementary material

Supplementary data for this article can be accessed on the publisher’s website.