Science Advisory Report 2016/046

Assessment of the impacts of an agricultural drain maintenance project on aquatic species at risk in Little Bear Creek, Ontario

Summary

• Proposed drain maintenance in Little Bear Creek, Ontario may negatively impact fishes currently listed under the federal Species at Risk Act (SARA), and/or their Critical Habitat.
• A macrophyte survey, bathymetry survey, and fluvial geomorphology survey were conducted on Little Bear Creek and provide relevant information used to predict the impacts of drain maintenance on fish species at risk.
• Trawling surveys, including both benthic and pelagic trawls, were conducted in Little Bear Creek across three time periods: summer, fall, and early winter to determine the abundance of fish species at risk, and to assess the effectiveness of the proposed timing window on mitigating exposure of species at risk to direct impacts of drain maintenance.
• Based on trawling surveys of Little Bear Creek, fewer fishes are expected to be directly affected by maintenance activities during the winter than the fall. The timing window (August 1–March 15) is outside spawning and egg incubation periods, yet not likely to avoid the early-rearing period for Pugnose Shiner and Blackstripe Topminnow (Fundulus notatus) or direct impacts to young-of-the-year fish species at risk.
• There is 0.032 km² of predicted suitable habitat, which exceeds the minimum area for population viability (MAPV) of 0.015 km² for Pugnose Shiner and 0.003 km² for Blackstripe Topminnow.
• Two drain maintenance scenarios were proposed for dredging of Little Bear Creek, the initial proposal and a revised proposal that had a reduced area proposed for dredging. Under both the initial and revised drain maintenance scenarios, 19% of suitable habitat in Little Bear Creek will be permanently lost. Temporarily lost suitable habitat will be 40% and 42% for the revised and initial drain maintenance scenarios, respectively. If regrowth of temporarily lost habitat does not occur, the suitable habitat that remains will be less than the MAPV for the Pugnose Shiner.
• To minimize the impacts of drain maintenance in Little Bear Creek, the most relevant mitigation pathway from Coker et al. (2010) is the dredging pathway (link 11–1 and 11–8).
• Habitat loss should be compensated through habitat gain of suitable habitat quality, and made accessible to the species within the first 2–3 years after impact (considering a generation time of 2 years and a maximum age of 3 years).
• For timing windows to be effective, dredging should occur when risk of direct mortality to fishes is lowest and outside the timing of spawning, egg incubation, and early rearing, which occurs in spring and early summer. Timing windows should be set based on biological information as opposed to dates.
• Macrophtyes removed from areas where the post-maintenance depth will be < 1.425 m are expected to grow back 1–2 years after drain maintenance. Future research should include post-maintenance vegetation surveys to better understand regeneration trends of aquatic macrophytes following drain maintenance activities.
• Due to a lack of bathymetry farther than 11 km upstream, there are no quantitative predictions of suitable habitat in these areas. Further research should incorporate drone work (previously conducted by DFO’s Fisheries Protection Program) on Little Bear Creek to supplement missing data.

This Science Advisory Report is from the May 11, 2016 regional peer review of the Impacts of an agricultural drain maintenance project on aquatic species at risk in Little Bear Creek. Additional publications from this meeting are posted on the DFO Science Advisory Schedule.

Complete document (PDF, 847 KB)

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