Indian Time - A Voice from the Eastern Door

Invasive Species Found in Akwesasne Waters


An up-close photo of the invasive species 'tench.' An adult tench can grow up to about 27 inches long.

On Tuesday, October 23, 2018, the Massena Courier Observer reported two invasive species were found nearby, it read in part, "Matthew Windle, an aquatic biologist with the St. Lawrence River Institute, Cornwall, Ontario, said members of the St. Regis Mohawk Tribe captured two tench, a Eurasian fish that can threaten native species and water quality, on Sept. 27 south of Cornwall Island."

Great Lakes Connection (GLC) reported, "Eurasian tench, an invasive species found in Canada and the United States, has been rapidly expanding its range into the St. Lawrence River in recent years. Its upstream spread has reached as far west as Lake St. Francis in southeast Ontario. Great Lakes researchers, scientists, and resource managers are concerned the tench could wreak havoc on native fish and their habitat if it enters the Great Lakes.

Tench are native to Europe and western Asia and were introduced to North America by the U.S. Fish Commission in 1877 for use as a food and sport fish, according to the US Geological Survey. That effort continued into the 20th century, but in most areas where the fish was introduced, it did not become established. However, a population introduced illegally to the Richelieu River by an unlicensed fish farm in 1986 has spread rapidly to the St. Lawrence River and Lake Champlain, according to McGill University Ph.D student Sunci Avlijas, who has studied the tench.

Ever since the fish were first detected in the St. Lawrence River in 2006, Avlijas said, a monitoring program run by the Quebec government and commercial fishermen has been in place. The population has grown exponentially every year between 2009 and 2014. They've also spread downstream on the St. Lawrence toward Quebec City and upstream toward Lake Ontario.

Once established in an ideal environment, tench form dense populations. Avlijas said tench will eat a variety of macroinvertebrates – zooplankton, mollusks and mussels, insects, and crayfish – mainly from the water bottom, but in calm waters they'll even go to the surface for food. They also tend to kick up mud and sediment, reducing water quality. Aside from direct competition with native fish for food, tench also carry non-native parasites that aren't known to be present in the Great Lakes, Avljias said, making them potential disease carriers for native fish. Tench also are known for eating zooplankton that can keep algae in check, potentially worsening the amount and size of harmful algal blooms.

What's more, they can survive in low-oxygen environments, and cover themselves in mud to survive outside of water for a limited period, allowing them to be introduced into new water bodies, Avlijas said. There have been documented cases of tench being mailed in wet sacks and arriving alive a day later."

According to GLC, tench are a prime candidate for being transported by people.

While tench are eaten by native fish like walleye, northern pike, smallmouth bass, largemouth bass and bowfin, once they grow longer than about 12 inches (30 centimeters), they become too large for most predators to consume.

Once an invasive species becomes established in a new environment, it is very difficult, if not impossible, to eradicate. However, it may be possible to slow or block the spread of the species. Education and outreach are critical to ensure that people are aware of the rules that apply to moving live fish. Since tench are related to Asian carp, it's possible that similar techniques could be effective in containing the spread of tench, like electric barriers. However, according to GLC, testing specific to tench hasn't been done yet, and they noted that other species – like the endangered American eel – travel through the St. Lawrence River too, so any measures to block tench would need to keep the passage of these species in mind.

In Ontario, tench are not regulated as an invasive species. Rules that apply to all fish species in the province also apply to the tench: a fish can only be released into the water body it was found in unless the releasing person or organization has a license. The use of tench as a baitfish is also illegal in the province, and people are asked to alert the Ministry of Natural Resources and Forestry if tench are found in the wild by calling the Invading Species Hotline at 1-800-563-7711 or going online to http://www.EDDMapS/Ontario. More information can be found on Ontario's Invading Species Awareness Program website.

An aerial map of where the fish were found.

Matt Windle M.Sc. Aquatic Biologist St. Lawrence River Institute stated, "For the past four years we (SLRI) have worked in close partnership with the Mohawk Council of Akwesasne to survey fish communities in the Upper St. Lawrence River, and plan to continue this project for the near future. To give an example of our effort and scope, this past summer we surveyed 54 sites between Montreal and Kingston, captured and released 30,000 fish and documented the assemblages and habitat associations of 52 fish species. We haven't captured a single tench in our surveys yet but will be extra vigilant now that they have been documented so close to Cornwall.  Our project has created an important baseline of the existing fish communities, so moving forward we can note any changes that might occur as tench move into the area.  Unfortunately, the invasive round goby is already present throughout the river, so it is another step in the wrong direction for the ecosystem.  As far as I know, there is no plan in place to reduce their numbers, other than creating awareness among recreational fishers to report and remove any tench captured." 

The Saint Regis Mohawk Tribe's Environment Division stated they 'will continue to monitor this new invasive species, but at this time it is premature to develop a plan without knowing their full impact on the immediate environment'.


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