Science Advisory Report 2016/056

Evaluation of habitat restoration activities for species at risk fishes within Crown Marsh (Long Point Bay)

Summary

• Crown Marsh is a freshwater coastal wetland located in Long Point Bay, Lake Erie. It has been invaded by common reed (Phragmites australis), an invasive perennial reed species, which has led to reductions in native wetland plants and open-water habitat and has indirectly impacted taxa dependent upon these habitat features, such as fishes.
• To rehabilitate Crown Marsh, common reed was mechanically removed to create open-water ponds. However, the extent to which the constructed ponds act as ecological traps (i.e., preferred areas that have disproportionally high natural mortality or reduced fitness), with negative effects on fishes currently listed under the federal Species at Risk Act (SARA), was unknown.
• Fisheries and Oceans Canada (DFO) and the Ontario Ministry of Natural Resources and Forestry (MNRF) undertook a 3-year monitoring study to determine fish use and habitat quality of the constructed ponds.
• The constructed ponds were utilized by species at risk such as Grass Pickerel (Esox americanus vermiculatus), Lake Chubsucker (Erimyzon sucetta), Pugnose Shiner (Notropis anogenus), and Warmouth (Lepomis gulosus). These were found at low abundances in the newly constructed ponds. Inner Long Point Bay is listed as critical habitat for Eastern Sand Darter (Ammocrypta pellucida) and Spotted Gar (Lepisosteus oculatus), but these species were not captured in any pond throughout the study.
• The constructed ponds had no significant difference in species richness compared to reference ponds. There were significant differences in community composition between constructed and reference ponds. Reference ponds had a more stable fish community among years sampled.
• Based on the wetland fish index (WFI) assessment, where a score less than 3.25 indicates a degraded wetland, and a score greater than 3.25 indicates a healthy wetland, all of the constructed and reference ponds achieved a score greater than 3.25 indicating good wetland health.
• All of the ponds sampled had a connecting channel to Long Point Bay. Water remained in the channels throughout the year, providing fishes with access in and out of the ponds.
• The constructed ponds acted as nursery habitat for fishes. Twenty three young-of-year (YOY) and juvenile fishes were detected in the newly constructed ponds, including the four species at risk.
• Newly constructed ponds were shallower than the reference sites. Due to the observed high water temperatures in the summer, low dissolved oxygen concentrations, and the possibility of complete freezing in the winter, it is suggested that to satisfy restoration objectives from an at-risk fish perspective, the ponds should be constructed with a gradient with the greatest depth at the mouth of the connecting channel so fishes can exit the ponds during low water periods.
• It is recommended that a permanent channel be maintained for each pond to ensure fishes are able to enter and exit the ponds as needed based on seasonal influences. This will help promote the survival of fishes and prevent the ponds from functioning as ecological traps.
• Lake Chubsucker requires a minimum area for population viability (MAPV) of 100 ha. The current amount of area dredged is 84 ha, which would not support the MAPV of Lake Chubsucker if connections between the ponds and Long Point Bay are not maintained. If further dredging occurs, and the proposed target of 50:50 open water to emergent vegetation in Crown Marsh is reached, the MAPV for Lake Chubsucker will be achieved. The current amount of open water does support the Pugnose Shiner MAPV as it requires 5 ha.
• Population-level parameters for at-risk fishes utilizing the restored ponds were not considered in this study. Future work should be completed on the composition of fishes in channels, movement patterns of fishes, and prevalence of species at risk in piscivore diets. This will help develop a population model as it relates to population trajectories and extinction thresholds to further determine the net benefit of the ponds to species at risk and determine to what extent the ponds facilitate predation mortality. Also, a more refined description of the timing and spatial distribution of spawning and habitat use by YOY and juvenile fishes within the ponds and connecting channels is needed to help refine maintenance and dredging timing windows.
• This report describes studies conducted within ponds in the Crown Marsh in Long Point Bay. Pond creation projects have been undertaken throughout Long Point Bay, both within and outside Crown Marsh. Findings from this study would be applicable to pond creation projects within Long Point Bay, outside the Crown Marsh area.

This Science Advisory Report is from the May 4, 2016 Evaluation of habitat restoration activities for species at risk fishes within the Crown Marsh (Long Point Bay). Additional publications from this meeting will be posted on the DFO Science Advisory Schedule as they become available.

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