Conserving at-risk aquatic species in agricultural drains

Agricultural drains are used to remove water from, and to drain areas such as wetlands to create, arable lands. Surface agricultural drains can be natural waterbodies, typically channelized at field edges, or newly created linear waterbodies. These natural waterbodies are typically modified through mechanically deepening and straightening of channels and grading of banks to form trapezoidal cross-sections, resulting in the loss of riffle-pool sequences and a uniform hydraulic channel gradient. Subsurface (tile) drains are used to bury surface drains and waterbodies, particularly smaller waterbodies in headwater areas of watersheds, to increase the amount of arable land and to reduce erosion and overall maintenance (Stammler et al. 2013). In Canada, nearly 8 million ha of land is drained, and agricultural drains are used extensively across the southern part of the country. In southern Ontario, over 68% of wetlands have been drained by European colonists since the early 1800s (Penfound and Vaz 2022), and there is an estimated 48 373 km of constructed drains (OMNRF 2023). In addition, 15% of all surface watercourses in southwestern Ontario have been buried by tile drains covering 16 000 km² (Stammler et al. 2013), primarily since 1978 (Penfound and Vaz 2022).

Surface agricultural drains require maintenance to maintain flow to prevent flooding of fields, which can impact aquatic organisms and habitat. Drain maintenance typically includes dredging of the stream to remove all impediments to water flow, such as silt, accumulated sediments, and vegetation and return it to its original drain profile. This process typically requires heavy machinery, and, therefore, the removal of riparian vegetation for access to the drain. These activities constitute the removal of riparian and aquatic habitat that is essential for the aquatic organisms living in surface drains (Fig. 1). Conversely, tile drains require minimal maintenance; however, the need for sufficient tile drain outlets often increases the need for regular drain maintenance of upstream surface drains. Tile drains created by burying natural watercourses in headwaters directly destroy aquatic habitat and indirectly influence energy flow throughout the whole watershed by removing autochthonous sources of energy in the headwaters (Blann et al. 2009). The visual impacts on aquatic habitat are clear (Fig. 1), but studies of the impacts on aquatic organisms across a wide range of agricultural drain sizes are limited. In small headwater surface agricultural drains, Ward-Campbell et al. (2017a, 2017b) found that aquatic habitat was largely eliminated by drain maintenance, but the habitat and simple fish and macroinvertebrate communities largely recovered within 2–3 years to those in the drain prior to maintenance, which were likely already degraded compared to the original natural waterbody.

There has been an ongoing conflict between the perceived need for regular drain maintenance and its impact on aquatic habitat and organisms (Stammler et al. 2008). The drain community, consisting of municipalities, drainage engineers, and farmers, have contended that, because drains are constructed, they should not be considered aquatic habitat and, therefore, should be exempt from legal protection (e.g., Fisheries Act 1985). Stammler et al. (2008), using a before-after-control-impact (BACI) survey of drain and natural watercourses, concluded that the ecological function of drains, as measured by aquatic habitat and fish communities, is no different than in similar-sized, adjacent natural watercourses. This result supports recognition and protection of aquatic habitat in drains. However, in Ontario, the drain community further contended that the provincial Drainage Act (R.S.O. 1990) legally required them to maintain drains, in conflict with superseding federal legislation such as the Fisheries Act. Several events characterized this conflict and contributed to changes in the Fisheries Act. In 2011, under the Fisheries Act, Fisheries and Oceans Canada (DFO), prevented the draining of a flooded agricultural field in Saskatchewan because of the presence of spawning Bigmouth Buffalo, Ictiobus cyprinellus, a species of Special Concern in Canada (DeDekker and Kruchak 2011). In the same year, a federal politician toured the Niagara region of Ontario and asked about the excessive costs of mitigating the impacts of drain maintenance in Beaver Creek, an agricultural drain containing Grass Pickerel, Esox americanus vermiculatus, a species of Special Concern in Canada (NEM, pers. obs.; see Case Study 2). In 2012, the Fisheries Act was amended to exclude protection of aquatic habitat unless it was explicitly used by fish species of “commercial, recreational, or aboriginal (CRA)” importance (Hutchings and Post 2013), and species that support CRA fishes, species typically not found in headwater drains. In 2019, a new federal government revised the Fisheries Act to “restore lost protections” for all fishes and fish habitat by changing protection from serious harm to CRA fishes to prohibition against harmful alteration, degradation, and destruction of fish habitat and defining habitat as any waters frequented by fish (Imhof et al. 2021).

Although protections of non-CRA and related fishes and fish habitat were temporarily suspended by the Fisheries Act, 2012–2019, this was not the case for species listed under the Species at Risk Act (SARA), passed in 2002 (Species at Risk Act, SC 2002). SARA prohibits the killing, harming, harassing, capture, or take of listed species (Section 32) and the destruction of their habitat (Section 58). Some, but not all, provinces and territories have similar legislation to assess and protect species at risk (SAR) of extinction (e.g., Ontario Endangered Species Act 2007; ESA). In Canada, many freshwater fish SAR (assessed by COSEWIC [Committee on the Status of Wildlife in Canada] or SARA-listed) are found in areas of high agricultural activity and, hence, agricultural drains, because of both requiring warmer climates (Chu et al. 2015; Anas and Mandrak 2022) and wetlands themselves or their soils when drained. Agricultural impacts are among the greatest threats to freshwater fish SAR (Dextrase and Mandrak 2006; McKelvey and Mandrak 2023), and many fish SAR are wetland specialists greatly impacted by the loss of habitat due to draining for agriculture (Montgomery et al. 2018, 2020). Between 2009 and 2023, only 29 SARA permits related to “drain maintenance” were issued in British Columbia, 1 in Ontario, and 1 in Quebec (SARA Public Registry 2023) despite the extensive overlap between agricultural activities and aquatic SAR in Canada, suggesting that permits may not have always been requested for maintenance in drains with aquatic SAR. Many of the permits issued in BC were for drains in the Fraser Valley, where populations of Threatened Salish Sucker, Catostomus sp. are found, despite drain maintenance being identified as a threat, and mitigation techniques specific to drainage work outlined, in its recovery strategy (Fisheries and Oceans Canada 2020). Additionally, at-risk freshwater mussels occur in some agricultural drains in southern Ontario, but there is limited research on them in this area (T. Morris, DFO, personal communication, 2024). A search of the SARA registry revealed at least one permit to relocate an at-risk mussel, Liliput (Toxolasma cylindrellus) from an agricultural drain in southern Ontario prior to undergoing maintenance activities.

In Ontario, DFO currently manages drain maintenance using a classification system to determine the extent of oversight required (Kavanagh et al. 2017). Drains are classified into six categories (A–F) depending on flow permanency, activity timing window, fish community including sensitive species, and time since last maintenance (Table 1). Sensitive species generally include cold- and cool-water species, sport fishes, species deemed sensitive by the United Staes Environmental Protection Agency, and fish SAR assessed as Special Concern. The authorization (i.e., review and approved activities) of proposed maintenance is based on the municipal drain class. Drains with intermittent flow (Class F) do not require any authorizations for maintenance, drains with permanent flow containing fall or spring/fall spawning sensitive species (Class D) required site-specific authorization from DFO, and all other drains (Class A–C, E) require only class authorization as outlined in Kavanagh et al. (2017). Class B, D, and E drains are classified by the presence of sensitive species, yet only Class D drains and drains with fish or mussel SAR listed as Threatened or Endangered under Schedule 1 of SARA require site-specific authorization from DFO. Fish SAR classified as sensitive species are all spring spawners, except American Eel, Anguilla rostrata, and, if not found with fish and mussel SAR listed as Threatened and Endangered under SARA, the drains in which they are found would be Class E and would only require class authorization. It is not clear how a drain with American Eel, assessed as Threatened but not listed under SARA and listed provincially as Endangered, would be classified. Note that several species (Pugnose Minnow, Opsopoedus emiliae, Silver Shiner, Notropis photogenis, Warmouth, Lepomis gulosus), listed as sensitive species in Kavanagh et al. (2017), are now listed as Threatened or Endangered under SARA and should be removed from the sensitive-species list. For drain classes A–E and “unrated” drains, low-risk activities listed in appendix 3 of Kavanagh et al. (2017) do not require any authorization, only the following of best management practices by the proponent. Fish SAR present in drains can be potentially impacted by drain maintenance if the species is assessed by COSEWIC as at risk, but not listed under SARA; not known to be present due to insufficient sampling (i.e., imperfect detection = false negative); or, class authorizations or best-management practices for low-risk activities are neither followed by the proponent nor enforced by DFO, or do not sufficiently mitigate impacts. Based on the Constructed Drains layer in the Land Information Ontario (OMNRF 2023), 4267 of 113 189 (3.8%) of drain “segments” are not classified, 24 380 (21.5%) segments are classified as N/A, and 29 560 (26.1%) segments are classified as not rated (NR), resulting in a total of 58 207 (51.4%) segments not classified as Class A through F (Table 1; Fig. 2). Kavanagh et al. (2017) indicated that any “unrated” (i.e., not classified, NR, N/A) drain requires a site-specific review; however, if the activities are deemed low risk by the proponent, up to half of the drains in Ontario may be excluded from the application of the drain maintenance guidelines. Importantly, the DFO drain classification does not explicitly address other aquatic SAR such as mussels, arthropods, amphibians, and reptiles, which could be similarly negatively impacted.

Proposed maintenance of drains with SAR may also require provincial permits. The Ontario Ministry of Environment, Conservation, and Parks (MECP), responsible for administering the provincial ESA, indicates that impacts to SAR and their habitat should be avoided where possible but, if the impacts cannot be avoided, “many drainage projects may be able to shelter under the conditional exemption in Section 23.9 of O. Reg. 242/08” (MECP 2021). Furthermore, “projects that involve repair, maintenance, and improvement work under the Drainage Act may fall under this exemption and, if the exemption applies and conditions in the exemption are satisfied, are exempt from some prohibitions under the ESA (e.g., Drainage Act Section 74 or 78 requests)” (MECP 2021). In 2021, the Office of the Auditor General of Ontario concluded that permit applications to harm SAR are always approved and that, in 2020, 96% (893) of approvals to harm SAR and their habitats were conditional exemptions (OAG 2021); therefore, there is a high probability that any drainage project that impacts SAR would be granted an exemption to proceed. A search for other provincial and territorial policies regarding managing SAR in agricultural drains yielded policies, publicly available online, for only Alberta and British Columbia. The publicly available Drainage Management Guide (British Columbia Agriculture Council 2005) identifies drainage environmental concerns and best management practices, but does not mention SAR, likely because of a publication date soon after the enactment of SARA. However, the Stewardship Centre for British Columbia has an excellent, but not legally binding, drainage maintenance and stewardship document that addresses protecting fish SAR (Pearson et al. 2018).

The objectives of this paper are: (1) to identify the current challenges to protecting aquatic SAR in agricultural drains; (2) to identify potential conservation actions that can be undertaken to protect and restore aquatic SAR and their habitat in agricultural drains using three case studies as examples; and (3) to provide recommendations on how to better conserve and protect aquatic SAR in agricultural drains in the future.

Little Bear Creek is a tributary of Lake St. Clair located in Chatham-Kent, southwestern Ontario (Fig. 2). In 1886, the creek was excavated to function as an agricultural drain and has since undergone drain maintenance (major repairs and improvement) in 1919 and 1972. To date, because of drain maintenance, most of the stream has been mechanically straightened and has minimal bank stabilizing vegetation or riparian buffer.

Despite these modifications, Little Bear Creek supports a diverse assemblage of 61 fish species, including several species protected by the federal Fisheries Act and SARA and the Ontario ESA: Blackstripe Topminnow, Fundulus notatus (Special Concern SARA and ESA), Lake Chubsucker, Erimyzon sucetta (Endangered SARA and ESA), Grass Pickerel (Special Concern SARA and ESA), Pugnose Minnow (Threatened SARA and ESA), and Pugnose Shiner, Notropis anogenus (Threatened SARA and ESA) (Wiklund 2015). Little Bear Creek serves as critical habitat for Pugnose Shiner (Fisheries and Oceans Canada 2012) and is home to several at-risk reptiles, amphibians, plants, birds, and insects.

In 2012, the Municipality of Chatham-Kent submitted a drain maintenance request under the provincial Drainage Act to repair and improve the functionality of Little Bear Creek drain (including excavation of accumulated sediments and removal of trees and brush in the creek channel; Fig. 1a). This proposal triggered a process that would ultimately illustrate the complex nuances that arise when habitat that supports fish SAR also serves as an agricultural drain.

Montgomery et al. (2018) developed a six-step modelling-based approach to assess the potential impacts of proposed maintenance on two fish SAR, Pugnose Shiner, and Blackstripe Topminnow. Species surveys were conducted under a DFO License to Collect Fish (LCF) and SARA permit and reviewed and pre-approved by DFO’s Animal Care Committee. Species-specific habitat modelling was used to relate species abundance and presence/absence with submerged aquatic vegetation (SAV). Then, a spatially explicit habitat model was used to predict the current distribution of SAV throughout the creek and the loss of suitable habitat under multiple drain maintenance scenarios (altered channel widths and depths). This crucial step was made possible by having access to detailed proposed drain maintenance plans and underscores the value of intentional cooperation with proponents throughout this process.

The impact of drain maintenance was measured by two main variables: change in habitat quantity (the total area of suitable habitat) and fragmentation (distance between biologically important habitat patches). Both variables were assessed on multiple time scales to evaluate how dredging would impact the system temporarily and permanently (based on the ability of vegetation to regrow or not). Predicted suitable habitat was compared to the minimum habitat for population viability (derived from existing population viability analyses; Malcolm 2015; Venturelli et al. 2010) and distances between habitat patches were compared to biologically relevant parameters such as body size and home range.

By quantifying the impacts of maintenance through time at both individual and population levels, mitigation recommendations were tailored to various stages. For example, Montgomery et al. (2018) recommended reducing the proposed depth and width dredged to avoid disjunct habitat patches that would make access to SAV for predator avoidance and spawning difficult for Pugnose Shiner and recommended offsetting and compensation to occur within the generation time of Pugnose Shiner (2–3 years) to reduce the permanent loss of habitat to a level that would support a viable population.

To date, this project has not been authorized by DFO and the work has not been completed. However, extensive brushing of riparian vegetation was undertaken in 2019 (FM, pers. obs.), which has the potential to increase erosion and, consequently, increased turbidity, and stream temperatures.

If data or resources are limited, broadly applicable recommendations for drain-maintenance mitigation (e.g., timing windows, fish-exclusion techniques, and relevant pathways from Coker et al. 2010) offer a minimum measure to address the potential harm to aquatic species, including fish SAR. This case study demonstrates that system/species-specific modelling exercises allow for recommendations to be appropriately tailored to support long-term recovery and survival. However, the project was limited by lacking a standardized BACI survey to validate model predictions. Future projects should incorporate early communication with proponents and other stakeholders to jointly curate context-specific, active mitigation efforts to conserve at-risk fishes in agricultural drains.

Beaver Creek flows into Black Creek, a tributary of the Niagara River (Fig. 2). Approximately 9.2 km of the main branch of the Beaver Creek is designated as a Municipal Drain under the Ontario Drainage Act (Province of Ontario 1990). For over a century, drainage work has occurred throughout portions of the creek, including 1890 construction of the Zavitz drain, 1895 improvement of the outlets for the Schooley, Baer, and Zavitz ditches, and 1903 channel dredging/straightening and brush removal to increase channel flow velocity. Historical drain maintenance of Beaver Creek was justified as “necessary” and a “valuable improvement” from the wetland habitat that was perceived as “an unsightly appearance…in a more or less unsanitary condition” (Ross 1902).

In 2005, the Town of Fort Erie retained a Drainage Engineering firm and an Environmental Consulting firm to prepare an updated Preliminary Report under Section 10 and Section 78 of the Ontario Drainage Act (R.S.O. 1990). Specifically, the Preliminary Report (K. Smart Associates Ltd. 2011) was to determine the repair and improvement required for the Beaver Creek Drain and the Outlet Drain, determine what was required to update a 1903 Engineer’s report on the Beaver Creek Drain (Ross 1902) to allow for future maintenance of the Beaver Creek Drain, and determine what was required to address the environmental concerns relating to maintenance work on the Beaver Creek Drain and the Outlet Drain. One major environmental concern was the presence of species protected by the federal Fisheries Act and SARA and the Ontario ESA, including Grass Pickerel (Special Concern SARA and ESA) and unspecified freshwater mussel species. Overall, there are 37 fish species known from Beaver Creek (Colm and Mandrak 2021).

The channel works recommended as a part of the Drainage Engineer’s Preliminary Report (K. Smart Associates Ltd. 2011) consisted of drain-maintenance activities (channel dredging to establish a favourable gradient and vegetation grubbing to reduce channel friction; Fig. 1b) with Natural Channel Design (NCD) elements (Urban and Environmental Management Inc. 2011). NCD elements were integrated into the proposal to mitigate overall impacts of drain maintenance on Grass Pickerel populations and their habitat. Channel form was restored at key locations via activities that included culvert removal and floodplain reconnection via rocky-ramp installs. NCD mitigative elements included the creation of five deepened online pools, three partially connected (offline) pools or pocket wetlands, littoral shelves on two-stage trapezoidal channels, and the use of cabled large woody structures throughout 988 m of thalweg distance in the Main or west branches. Additionally, an area downstream of the engineered reach was amended using natural weirs (aka rocky ramps or Newbury weirs) to reconnect an entrenched channel reach (former forested wetland complex) to its abandoned floodplain, thus restoring channel to riparian overbank mobilization functioning. In this reach, a constricting box culvert was removed and a partially off-line pool/wetland with littoral shelves was installed. The east branch of Beaver Creek was left in its natural state and acted as a control reach.

To determine the potential impact of drain-maintenance and NCD-based reconstruction activities on Grass Pickerel habitat and abundance, BACI surveys were conducted (LCA Environmental Consultants 2011; Glass et al. 2021). Fish surveys (tagging of Grass Pickerel and seine sampling) were completed in 2009 and 2010 to generate baseline data prior to drain maintenance work in late 2011 and early 2012. DFO continued to monitor Grass Pickerel “post-maintenance”, through this period and into 2013 and again in 2015. Species surveys were conducted under the DFO LCF and reviewed and pre-approved by DFO’s Animal Care Committee. BACI results showed that Grass Pickerel populations declined from 2009 to 2013, throughout both the control and altered channels (Fisheries and Oceans Canada 2021a). This result highlights the importance of a well-planned pre- and post-construction monitoring program to avoid misinterpreting potential impacts and to reduce uncertainty. Despite overall population declines, Grass Pickerel recolonized the reconstructed section of Beaver Creek, which had higher relative abundance than control sites post-maintenance (Fisheries and Oceans Canada 2021a). The creation of deeper pools likely mitigated the cumulative effects of habitat alterations in 2011 and drought in 2012. However, it is unclear whether Grass Pickerel were dispersing from other reaches of the creek into the reconstructed section, or if increased production is occurring in the reconstructed section (Fisheries and Oceans Canada 2021a).

This case study demonstrates that proactively responding to drain-maintenance activities through incorporating NCD elements such as mitigation (e.g., creation of pool refuge habitat) and restoration (e.g., floodplain reconnection, removal of box culvert) techniques can limit the negative impacts to vulnerable fish SAR. NCD features (such as those that maximize channel complexity, allow submerged aquatic macrophyte to establish, create or re-establish functioning floodplains, or reconnect abandoned floodplains) should be incorporated into maintenance activities in drains with Grass Pickerel and other fish SAR present. This case study underscores the value of incorporating not only mitigation, but also restoration, techniques with drain-maintenance work through close collaboration with stakeholders and biologists. Looking forward, practitioners, stakeholders, and biologists should anticipate future maintenance work and proactively incorporate techniques that build resiliency into systems so vulnerable species like fish SAR can better withstand future maintenance work.

Rondeau Bay, a coastal wetland along the north shore of Lake Erie, Ontario, Canada, is an aquatic species-rich area stressed from several dominant anthropogenic threats, including wetland loss due to drainage, extensive agricultural activities throughout the watershed, and invasive species (Fig. 2). The wetlands in the bay are faced with a variety of threats caused by agricultural practices (e.g., wetland drainage, nutrient runoff) and the presence of invasive species known to degrade habitat suitability (e.g., Common Carp, Cyprinus carpio, European Common Reed, Phragmites australis). To maximize agricultural productivity on the northeast corner of Rondeau Bay, several agricultural drains with adjacent pumping stations were created in the 1900s, including the McLean Drain in 1925, Holdaway Drain in 1941, Bates-Bloomfield Drain in 1980, and Branch 1 Drain in 1967 (B. Chevalier and K. Tippin, personal communication, 2023) (Supplemental material, Fig. S1).

The bay is a provincially significant wetland and a proposed freshwater key biodiversity area (WCS 2021), with 81 fish species (including 13 SAR), 7 turtle species (6 SAR), and 22 mussel species (13 SAR) found in Rondeau Bay and the surrounding wetlands (OMNRF and Ontario Parks 2012). The agricultural drains have been identified as critical habitat for federally listed fish SAR, including Spotted Gar, Lepisosteus oculatus (Endangered SARA and ESA) and identified as potential habitat for several other fish, turtle, and mussel SAR including Warmouth (Special Concern SARA; Endangered ESA).

To combat the conservation challenges that Rondeau Bay is facing, and to promote the conservation and recovery of aquatic SAR, St. Clair Region Conservation Authority has proposed restoration activities for the creation of drain-adjacent wetland habitat through the conversion of agricultural fields back to wetland habitat and the removal of European Common Reed to expand and diversify wetland habitat within existing agricultural drains. To create 2.4 ha of Spotted Gar spawning habitat, agricultural fields adjacent to the main channel of the McLean Drain were retired in 2022 and connected to the main channel flowing into Rondeau Bay in 2023 (Fig. 1c). Furthermore, the clearing of 27 ha of European Common Reed in the municipal drain starting in 2023 will create more habitat available to Spotted Gar and other fishes in the bay.

A BACI survey (Underwood 1992) is being implemented in four municipal drains, the restoration area where Spotted Gar spawning habitat will be created, and a large open-water area adjacent to the McLean Drain (Fig. 1c). The current distribution of fish SAR and their habitat will be assessed to inform restoration activities and to monitor the effectiveness of restoration through the comparison of degraded control sites (drains and degraded wetlands) with the impact (restoration) site. Species surveys were conducted under the Ontario LCF (100584, 1102792) and SARA permits (22-PCAA-000027, 23-PCAA-00003) and reviewed and pre-approved by the University of Toronto’s University Animal Care Committee.

Both at-risk fishes, Spotted Gar and Warmouth, were found in agricultural drains and adjacent open-water areas with shallow, moderately vegetated habitat that seasonally progressed to highly vegetated, consistent with their known habitat requirements (COSEWIC 2015; Fisheries and Oceans Canada 2021b). Specifically, in 2022, several life stages of Warmouth were detected in all sampling locations except Branch 1 and Holdaway drains. In 2023, Warmouth was only detected in the McLean Drain and adjacent open-water area. In 2022 and 2023, adult Spotted Gar were detected in all sampling locations except for the restoration area, which likely could not be accessed by larger bodied Spotted Gar. Capture of larval Gar in 2022 and 2023 (Supplemental material, Table S1) indicates that Spotted Gar are successfully reproducing in all areas except for the open-water and restoration areas.

While restoring connectivity between agricultural drains and adjacent wetland habitat is an important step, successful restoration initiatives must ensure good quality habitat to maximize reproduction and avoid creating an ecological sink. In this case study, access was restored, but high turbidity levels in the open-water area (2022 average: 33.9 Nephelometric Turbidity units (NTU), 2023 average: 25.6 NTUs) may have prevented successful reproduction, as Spotted Gar hatch-rate success is known to decrease by 24% under turbid conditions (five NTUs) (Gray et al. 2012). Additionally, the presence of aquatic invasive species (AIS) can play a role in reducing the suitability of reconnected habitat. For example, Common Carp increase turbidity and decrease vegetation in wetland ecosystems (e.g., Lougheed et al. 1998; Peterson et al. 2022), thus their presence in Rondeau Bay may greatly alter restoration sites that serve as Spotted Gar spawning habitat (McAllister et al. 2023).

Despite the restoration of connectivity resulting in the emergence of more complex, dense aquatic habitat, and higher species richness and abundance (DR, pers. obs.) (Supplemental material, Table S2), the presence of many invasive plant species, such as European Common Reed, Flowering Rush, Butomus umbellatus, and European Frog-Bit, Hydrocharis morsus-ranae, and the invasive leuciscid-dominated fish community, suggest that the newly created area is currently a degraded wetland with low ecological resilience. Thus, connecting naturalized wetland habitat, enhancing wetland habitat prior to restoring connectivity, or the more rigorous selection of newly connected sites that are less degraded, paired with AIS exclusion techniques, should be incorporated into future restoration initiatives to create ecologically resilient habitats suitable for native species (such as Spotted Gar and Warmouth) at risk of impacts from agricultural drains and other habitat degradation. Furthermore, monitoring this study, and others like it, into the future would allow for a more comprehensive understanding of how the aquatic community responds over time to the newly created habitat.

The creation of new habitat and the restoration of existing habitat within, and adjacent to, municipal agricultural drains present an opportunity to develop resiliency and compensate for future ecological impacts by restoring, creating, or enhancing habitat, referred to as habitat, or conservation, banking (Hunt et al. 2011). While maintaining ecosystem functioning, the prevention of wetland loss and development of ecological resiliency are also proactive measures to maintain good ecosystem function in the face of climate change (Moomaw et al. 2018). Because restored wetlands do not function as well as natural wetlands (Meli et al. 2014), an emphasis should be placed on protecting natural wetlands for habitat banking before restoring them. In the cases where proactive habitat banking is conducted through the enhancement or restoration of degraded agricultural drains and adjacent land, activities that promote environmental variation, maintain hydrological connectivity, or preserve biodiversity hotspots should be considered with the use of basin-wide assessment and analyses (Grantham et al. 2019).

The first case study, modelling potential impacts of drain maintenance in Little Bear Creek, highlights an adaptive framework to minimize impacts of habitat alteration using ecological modelling approaches. The case study in Beaver Creek, demonstrates integrative techniques that can be used to actively mitigate drain maintenance and use the opportunity to undertake additional restoration work, resulting in a net gain of habitat. The third case study, restoration of agricultural lands and drains in Rondeau Bay, moves beyond mitigation toward innovative, pre-emptive techniques to build resilient systems that may inevitably face challenges associated with fish SAR living in agricultural drains. While these reactive, active, and proactive measures can help to balance management needs of fish SAR and agricultural drains, we have additional recommendations to achieve long-term aquatic ecological function, productivity, and biodiversity.

The paradox of managing a waterbody governed by two acts that have contradictory requirements (one to protect species’ habitat from destruction, the other to alter it significantly) will likely be an ongoing issue in southern Ontario, given the high concentration of aquatic SAR (Mandrak and Cudmore 2010; Chu et al. 2015; Anas and Mandrak 2022) and agricultural land/development (Snell 1987; Ducks Unlimited Canada 2010). Although not necessarily the result of conflicting legislation, similar antagonisms are undoubtedly occurring in other areas in Canada with aquatic SAR in agricultural areas. Lessons learned from Ontario offer an opportunity to improve management of these systems elsewhere. Additionally, more research is needed to better understand the impact and extent of drain maintenance on freshwater mussel populations in Canada, to improve management of at-risk species (Sousa et al. 2021). Together, sound legislation and policies enacted to protect aquatic SAR, meaningful and early collaboration among researchers, stakeholders, and proponents, and innovative mitigation, recovery, and restoration solutions will help balance the need to protect and recover aquatic SAR with the need to manage agricultural drains.

We thank Jordan Rosenfeld and Mike Pearson for providing information of drain management in British Columbia, and Craig Paterson and Alex Van Nynatten for assistance with the Rondeau case study.