The fishway is doing its job
It may look like a small lake, but Cootes Paradise marsh was once nearly covered from end to end with aquatic vegetation.
In the 1930s, plants covered about 85 per cent of the marsh. By 1984, this had declined to 15 per cent and most of the remaining plants were non-native invasives. The vegetation is vital for many fish, birds, small mammals and other animals that are all part of a healthy ecosystem. Restoring Cootes has long been a goal for Royal Botanical Gardens and its partners, and it’s vital.
Getting Hamilton Harbour off the list of areas of concern for pollution around the Great Lakes depends on the recovery of Cootes Paradise. If Cootes Paradise, a nationally important bird area, an important amphibian and reptile area and part of the Niagara Escarpment World Biosphere, isn’t healthy, the harbour isn’t either.
What brought about this decline? As early as 1870, common carp, large, oily fish from Europe and Asia, were released from a hatchery to replace native Atlantic salmon, already in decline in Lake Ontario. By the 1930s, carp were the dominant fish in Cootes Paradise and other Lake Ontario coastal wetlands. Not only did they grow in numbers, they modified the marsh by churning up sediments during spawning, choking out those vital aquatic plants. By the 1980s, biologists estimated the biomass of the carp — their combined weight — might have been as much as 800 kilograms per hectare, a staggering 240 metric tons of carp in Cootes Paradise alone.
Despite the numbers, there was good news. Most of the carp leave the marsh every year after spawning, through the narrow Desjardins Canal, the only connection to Hamilton Harbour. If the returning carp could be intercepted at that point each spring, the marsh could be protected and allowed to recover. The Cootes Paradise Fishway was put into operation in 1997 to block the carp. If you’ve walked along the Waterfront Trail between Princess Point and Pier Four Park, you’re likely familiar with the Cootes Paradise Fishway, looking a bit like a bridge topped by overhead cranes.
The idea of the fishway is simple. It’s a fish sieve. Any fish wider than five centimetres are caught in steel baskets under the structure. It is a two-way barrier with the ability to move fish into and out of the marsh. This is key, because the fish live in the lake and the harbour and they only migrate into the marsh to spawn. The warm productive waters of the marsh then act as a nursery ground for all the baby fish produced. When the fishway is operating, baskets are left open overnight then pulled out of the water with the cranes and dumped into a large holding tank where the fish can slowly be identified, counted and released. There are two shoots to direct fish, which allows biologists to block invasive fish species from entering the marsh while still allowing native fish access.
In 1997, the first year it was in operation, 17,861 fish moved through the fishway, and 82 per cent of these were carp and other non-native species. In 2022, the total was 15,847 fish through, of which nine per cent were the non-native carp and their relatives, and 15,249, or 91 per cent, were native species. The total numbers vary each year, but the proportions have been stable for the past decade. With the carp population dropping, shallow areas of the marsh have proven resilient.
With some planting, aquatic vegetation like cattails and water lilies have made a rebound. Even wild rice, a once prolific species and a staple for feeding wildlife and Indigenous people, is now growing in the marsh.
The fishway also catches its fair share of oddball organisms. According to Tys Theijsmeijer, RBG’s senior director of ecosystem stewardship programs and policy, the weirdest capture was a Chinese mitten crab, an escapee from captivity, some years ago. Another astonishing visitor to the fishway that’s a favourite of RBG’s aquatic ecologist Jennifer Bowman is the occasional American eel. These slender fish migrate inland to Lake Ontario to spawn from the Sargasso Sea in the middle of the Atlantic Ocean. Even the occasional Atlantic salmon shows up.
Members of the public are always welcome to visit the fishway, which is in operation by mid-April. Watch for notices on the RBG website for specific dates and times, including for demonstrations where additional interpretation of the action is available.