No 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.

Background: Acoustic transmitters are widely used to obtain information on the spatial ecology of fish and other aquatic animals. Some transmitters contain pressure sensors to estimate depth, which are factory-calibrated before being sold and have a specified range of error. Our goal was to assess the accuracy of these pressure sensors and the factory calibrations to assess whether researchers should conduct additional calibrations prior to use in the field. To evaluate error, we conducted calibrations on ten acoustic transmitters with pressure sensors (obtained from Vemco-Amirix Ltd.) both in the laboratory (pressure chambers at Hammond Bay Biological Station and Carleton University) and in the field (based on lowering tags to known depths in Toronto Harbour and Experimental Lakes Area). Slopes, intercepts, and R 2 values of researcher-calibrated sensors were compared to the factory-calibrated values to contrast calibration methods and identify directional biases. To estimate the effects of temperature on sensor performance, we calibrated the same sensors at varying temperatures and compared slopes, intercepts, and R 2 values. Finally, we evaluated external effects (i.e., water temperature, salinity, and atmospheric pressure) on sensor output through simple modeling exercises to better understand potential sources of error. Results: A significant difference was found among the slopes and R 2 values of the four calibration events, whereas no difference was found among the intercepts. There was also a significant effect of calibration water temperature on slopes, intercepts, and R 2 values. External effects should be taken into consideration when interpreting biological data as they have an effect on hydrostatic pressure thereby affecting the reported depths (1.77 m shallower to 6.47 m deeper than standard conditions). Conclusions: Nonetheless, we did not find sufficient evidence to support the need for additional calibrations beyond those provided by the manufacturer as they did not markedly increase the accuracy of depth estimates.

Every year billions of dollars are being spent on rehabilitation activities in hopes of improving the state of degraded ecosystems. In this thesis, I considered the practical aspects of acoustic telemetry for studying habitat enhancement and investigated the effectiveness of habitat enhancement initiatives in Toronto Harbour by comparing fish habitat use of six species in two enhanced slips to two non-enhanced slips. During spring, Northern pike were found to spend more time in the enhanced slips compared to the nonenhanced slips. All other species did not spend significantly different amounts of times across the slips. When Largemouth bass and Northern pike were experimentally displaced in the enhanced slips, they left within 29 hours suggesting that the enhanced habitats did not provide substantial direct benefits to adult fish in this study. Overall, telemetry studies with good experimental designs are considered valid tools for management.iii