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CARPe Diem: Seizing the Bay back from invasive fish
BY Emily Bootsma
ON June 2, 2018
   What is the Fishway? You have probably seen its odd, metallic bulk spanning the canal between Hamilton Harbour and Cootes Paradise as you drive by on the 403 or the York Boulevard bridge. You may know that the Fishway is a source of pride for many in Hamilton, but do you know why? What does it really do? As you may be able to guess by its name, it has something to do with fish. In particular, its main function is to deal with the invasive common carp.
 
   
The common carp (Cyprinus carpio) is a non-native species of fish that harms the Cootes Paradise Marsh ecosystem. Originating from temperate regions of Asia, common carp were first introduced into Lake Ontario in the 1870s to stock fish hatcheries. Carp mature quickly (at around two to four years of age), reproduce prolifically, and can reach sizes of 110 cm and 40 kg when full grown. While this make them an efficient food source in many areas of the world, it also makes them a threat when introduced into a system like our marsh. In the early 1990s we began to see the harmful effect of their introduction, when the amount of carp in Cootes Paradise reached densities of 800 kg/ha, or more then 50,000 carp.

   Carp are harmful to their environment for multiple reasons. As bottom-feeders, carp find food by shoving their heads into the muck at the bottom of the marsh and using their sucker-mouth to take in the sediment. They then filter out any wanted food particles they find (such as worms, mollusks, insects, and seeds) and expel the remaining sediment through their gills. This stirs up the sediment and muddies the water, making it difficult for other fish to find food and decreasing the amount of sunlight that can reach plants growing in the marsh, stunting their growth. The disruptive feeding of the carp also uproots the valuable marsh plants. Carp further damage the marsh when they spawn in the spring. A female carp will be pursued by up to twenty males, all thrashing and jumping about in the water. The female can also release 1,000,000 eggs at once, which will adhere onto plants. The weight of the eggs and the thrashing of so many large fish further damages marsh plants. Common carp were responsible for a decrease in vegetation from 90% to only 15%. Vegetation makes up the base of the marsh food chain and provides shelter for many animals, therefore a loss of plants will result in ecosystem collapse.
  
 Fortunately, the marsh has been saved  from  through the brink of destruction by a brilliant installation: the Cootes Paradise Fishway! First built in 1996 and run by the Royal Botanical Gardens, the Fishway is located in the Desjardins Canal, the  only water bridge connecting Cootes Paradise to Hamilton Harbour. Its  functionality is based in the fact that every fall, carp leave the marsh to  spend their winter in the deeper, unfrozen, water of the harbour before returning to the marsh, in   spring, to spawn. The Fishway is designed to catch adult carp as they swim from the harbour into the marsh. When carp reach maturity, they are quite large, and so the Fishway  is built to monitor any large fish (>35 cm) attempting to enter or exit the marsh. Smaller fish are able  to swim the Fishway’s 5 cm metal grating, while large fish are caught in 
underwater baskets. These baskets are then lifted out of the water,  allowing Fishway workers to hand sort t the fish. They send carp back into the harbour and allow native species to freely move in and out of the marsh.. Keeping the carp in the harbour is beneficial as without access to the marsh for spawning, the population is naturally declining. 
 
Since the addition of the Fishway to the Desjardins canal, the quality of Cootes Paradise Marsh has increased infinitely. More than 95% of carp have been excluded from the marsh. Their exclusion has resulted in increased native fish populations, improved water clarity (as the sediment is not being stirred up) and plant regrowth. Aquatic plants have increased from 0 hectares to 80 hectares and wetland plants have increased by 105 hectares! You too can help increase vegetation cover by joing BARC for one of our volunteer marsh plantings.
 
The Fishway is open to the public so we encourage you to go see the fishway in action. Maybe you can get up close and personal with a common carp. In May and June, lifts are schedule Monday to Friday for 7:30am and 2:00pm. In July and August, lifts are scheduled for Mondays, Wednesdays and Fridays at 2:00pm. Check out their special weekend lifts on Fathers day (Sunday, June 17th) and Hamilton’s Fishing Derby (Saturday, August 11th). (Please give yourself approximately 10min to walk down to the fishway from the Princess point parking lot located at the end of Macklin Road South. So drop by the Fishway and experience for yourself one of the major restoration efforts that has allowed Cootes Paradise to return to the beautiful, thriving marsh that it is today!

 
Sources

Bowen, Kelly and Tys Theysmeyer. The Cootes Paradise Fishway: Carp Control Techniques at Royal Botanical Gardens, Hamilton, Ontario, Canada. Royal Botanical Gardens. https://www.rbg.ca/files/pdf/exploreandlearn/naturallands/fishway.pdf

Carp Elimination. Royal Botanical Gardens. https://www.rbg.ca/files/pdf/exploreandlearn/naturallands/carpelimination.pdf.

Common Carp Backgrounder. Royal Botanical Gardens. file:///D:/BARC/Common-Carp--- RBG-2017.pdf

The Fishway. Royal Botanical Gardens. https://www.rbg.ca/fishway. Accessed May 14, 2018.

 
Author Bio - Emily Bootsma
Emily is a spring intern at BARC.
Emily is a spring intern at BARC.

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