Fish futures

In Atlantic Canada, DUC’s wetland restoration work often includes installation of water control structures to regulate water levels. In cases where these structures could be barriers to fishes, DUC also constructs fishways. DUC currently manages or co-manages over 150 fishways in the region—which help fish access habitat upstream — and has become a go-to expert assessing if fishways pass fish as intended. Their understanding of how fish navigate fishways has enhanced structure management and designs.

Some native species, such as American eel, Atlantic salmon, alewife and rainbow smelt, need freshwater and marine habitats to complete their life cycles. Therefore, increasing river connectivity using fishways is critical. When migrating from the ocean to freshwater, these fishes bring marine-derived nutrients as part of their body, eggs, sperm and/or excrement. These imported nutrients improve freshwater wetlands by fuelling food webs, increasing growth of bacteria, plants, invertebrates — and yes, ducks too.

One exemplary project is Missaquash Marsh. Located on the Chignecto Isthmus — the low land joining Nova Scotia and New Brunswick — this large wetland has exceptional biodiversity that benefits many human activities, such as boating, angling, trapping, hunting and birdwatching. The area also supports commercial fisheries. Since 2013, DUC staff and associates have conducted alewife tagging and tracking in rivers of the Chignecto Isthmus. With more than 14,000 individuals tagged, the data set continues to be used to evaluate water control structures and their impact on fish passage, with added value information on alewife migration, life expectancy, feeding behaviour and population dynamics.

This research is about more than just fish, as this knowledge has and continues to be applied to improving water control structures, increasing river connectivity and enhancing the nutrient flow within freshwater wetlands of Atlantic Canada, which is good news for both the finned and feathered.

Mitigating Howe Island

There’s plenty of fish in the sea — or in this case, the Johnson Bay wetland on Howe Island — thanks to a DUC fish habitat project.

When Ontario’s Ministry of Transportation contacted Mike Williams, DUC’s manager of Conservation PRO (DUC’s professional environmental services arm), about a project to compensate for impacts to fish habitat caused by upgrades at the Wolfe Island ferry terminals, he embraced the challenge and began searching for a suitable property to support the project. DUC was able to acquire a large undeveloped area on Howe Island — located east of Kingston, where Lake Ontario meets the St. Lawrence River — and the stars aligned for one of DUC’s largest Conservation PRO projects in Ontario.

With Conservation PRO, DUC offers a turn-key approach to habitat restoration projects that are required as a condition for development project approvals; handling everything from finding the site to project design, approvals negotiation, permitting, implementation and monitoring.

Williams and his team expertly enhanced the wetland by creating a series of interconnected pools and channels to make the marsh more fish friendly. Then the exciting part of the project began: monitoring for success. To ensure objectivity and expert advice, DUC partnered with Quinte Conservation to complete the monitoring.

The results exceeded expectations. In the first year of monitoring, 13 native fish species were observed using the habitat (including grass pickerel, a species listed as Special Concern), surpassing the Department of Fisheries and Oceans requirement of five native fish species.

In the second year, 11 species were recorded, including two new ones (rock bass and tadpole madtom) not observed the previous year. Pumpkinseed, brown bullhead, bluegill and yellow perch were observed, with an uptick in golden shiner in the second year. Largemouth bass and northern pike were also present. DUC staff also saw Blanding’s turtles basking in the new channels and noticed wild rice starting to grow, which will help feed a wide variety of marsh birds. After three years, the total count was 1,130 fish from 16 different species. DUC detected fish from young-of-the-year to adults in the new habitat, indicating that all life stages were using it.

When an activity will result in damage to our ecosystems — important natural areas that support biodiversity and climate resilience — we must ensure that we compensate for those impacts in a way that leaves our landscape healthier than before. A well-planned habitat restoration effort can provide increased overall benefit for wildlife and the landscape in the long term.

Clearing out carp in a coastal wetland

Common carp is a freshwater invasive fish known for its destructive feeding and spawning habits. In wetlands, they stir up sediment, reducing water clarity and damaging underwater plants, which serve as an important source of food for migrating waterfowl in the fall.

The presence of invasive common carp, along with other factors, led to the degradation of Delta Marsh in Manitoba — a large freshwater coastal marsh with significant ecological and cultural value.

In 2009, DUC launched a long-term study with many collaborators and stakeholders to limit the access of large common carp to Delta Marsh. The goal was to restore the wetland to historical conditions, similar to those seen in the 1970s, to support fall-migrating waterfowl.

DUC and partners set out to test whether carp exclusion structures could block large carp from accessing the marsh without harming native fish. The project involved building dikes and installing carp exclusion structures across four channels that connect the marsh to Lake Manitoba. Three existing culverts were also modified with bar screens.

The structures were built in the winter of 2012-2013 and remain in place year-round. Each spring, bar screens were slotted into the structures to block large carp attempting to enter the marsh during their migration and spawning period. The screens were removed mid-summer once spawning ended. Native fish species like northern pike and walleye typically migrate earlier and could pass through before the screens were installed. A habitat and fish community monitoring program ran until 2018.

The results speak for themselves. Without the large carp stirring up sediments, water clarity improved significantly, and the area covered by underwater plants doubled over the six years of monitoring.

The return of healthy aquatic habitat led to a resurgence of fall-migrating waterfowl. Diving duck density increased by 339 per cent, and dabbling duck density rose by nearly 400 per cent compared to pre-exclusion levels in the 2000s.

Findings from this study, published in 2024, offer valuable insights for habitat managers worldwide working to control invasive carp and restore healthy aquatic ecosystems. The study was so successful that the use of the exclusion structures has been operationalized for the long term, with the Province of Manitoba overseeing their ongoing use.

Restoring habitat for salmon

The Fraser River Estuary of B.C. is home to hundreds of millions of out-migrating juvenile Pacific salmon that rely on these tidal ecosystems as they transition to the ocean. Together with Boundary Bay, the estuary is also the most important overwintering area for waterfowl in Canada.

In addition to being key to the B.C. economy and Indigenous ways of life, Fraser River chinook salmon are the primary prey of endangered southern resident killer whales.

Scientific investigations have shown that river training and dredging have changed how the river naturally distributes new sediments to the estuary. These sediments are the foundation allowing the estuary to grow vertically to keep ahead of rising sea levels that put ecosystems and communities at risk.

DUC is leading a team to implement the Sturgeon Bank Sediment Enhancement Pilot Project that’s aimed at restoring tidal marsh fish habitat and building marsh resilience to keep pace with rising seas. Sturgeon Bank has lost over 395 acres (160 hectares) of tidal marsh since the 1980s. Restoring sediment supply is essential, not just for the marsh itself, but for everything it supports: Pacific salmon, migratory birds, carbon storage and flood resilience for surrounding communities.

Work crews are repurposing sediment dredged from the Fraser River and, using a large hose, placing it in key areas on the bank. The natural process of waves, winds and tides will distribute these sediments throughout the foreshore. The goal is to restore valuable wild Pacific salmon tidal marsh habitat, which supports many different fish and wildlife species.

This pilot project is an opportunity to test and evaluate a local, customized approach to address large-scale tidal marsh loss. DUC and partners hope to apply the design and lessons learned from this pilot project to other areas of the Fraser River Delta and other estuaries in B.C.