Fish community structure varies by location and presence of artificial islands: a case study in Hamilton Harbour, Lake Ontario

Abstract

Abstract  Artificial islands and reefs have been used in the Laurentian Great Lakes for over 40 years as a means of improving aquatic habitat; but research on their efficacy has primarily focused on their ability to increase the abundance of specific sportfish, top predators, or other keystone species. To understand the importance of islands in structuring the whole fish community, we took a holistic approach and analysed the effect of islands, location, and the interaction effect between the two in structuring fish communities in Hamilton Harbour, Lake Ontario using a 30-year electrofishing dataset. The effect of islands varied by location within the harbour, with some species showing a preference for islands in some locations while avoiding them in others. Island communities also tended to have significantly different species compositions, with higher index of biotic integrity scores and species richness, greater numbers of pollution intolerant fishes, centrarchids, and fewer generalist species. However, these results paled in comparison to the level of inter-annual variation in the fish community of the harbour, which has changed markedly over the 30-year time span. Taken together, our results highlight that while island creation can influence the fish community, the type and magnitude of effect will vary based on their distance to other suitable habitats (i.e., location within the system) and the design of the island itself. Further, the noted inter-annual variability emphasizes the importance of considering long time scales (> 10–20 years) when exploring fish community responses to habitat creation. Collectively, these results will help the design of more effective management strategies for restoring fish communities.