Assessing occupancy of freshwater fishes in urban boat slips of Toronto Harbour

Abstract

Hardening of natural shorelines in urban aquatic ecosystems can result in a loss of fish habitat and productivity. The north shore of Toronto Harbour (Lake Ontario) has been converted to hardened boat slips for commercial, industrial and recreational purposes, but its potential utility as fish habitat has not been evaluated. The objective of this study was to determine whether fish frequented and utilized four slips in the Inner Harbour of Toronto. Two western boat slips are adjacent to some natural features and have undergone some rehabilitation to increase the complexity of aquatic habitat (i.e. addition of large substrate, overhead cover, and in-water structure). In contrast, the two eastern slips are deeper and more influenced by the turbid Don River. We assessed the timing and duration of occupancy within all four slips for seven fish species using acoustic telemetry. In just under a year, tagged fishes spent a limited amount of time in any one slip. However, there was evidence for increased use at the two western slips by Northern Pike (Esox lucius) in spring, which is likely linked to the proximity of these slips to a known spawning area. Overall, there was no reliable evidence that the majority of the seven adult fish species evaluated frequented either the western or eastern slips. Despite efforts to track and tag a variety of species, insufficient detections prevented a detailed assessment of habitat selection for the majority of species of interest. A more detailed study of the spatial ecology of these fishes is therefore needed to understand the scale of their habitat use and inform the design of habitat rehabilitation projects for hardened shorelines.

Keywords:

• acoustic telemetry
• hardened shoreline
• multi-species
• spatial ecology

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Acknowledgements

The authors thank all of the Toronto and Region Conservation Authority employees that have helped with field work (Adam Weir, Pete Shuttleworth, Brian Graham, Ross Davidson, Emily Morton, and the rest of the TRCA team).

Funding

This study was funded by NSERC, Great Lakes Sustainability Fund, Toronto and Region Remedial Action Plan, Great Lakes Fishery Commission, Ontario Ministry of Research and Innovation, Ontario Ministry of Natural Resources, the Canada Research Chairs program, Fisheries and Oceans Canada, and the Great Lakes Action Plan.

Supplemental material

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

References