Commercial tench fishing could help control the invasion of this species in the St. Lawrence River and benefit…the Biodôme’s animals!
The invasion of our water systems by invasive fish species can affect the quality of the water, habitats, nutrient cycles, the amount of contaminants, biodiversity and productivity via a great variety of mechanisms ranging from trophic disruption to disease transmission. Tench (Tinca tinca), a freshwater fish, is a cyprinid native to Europe and Asia that has been introduced into a number of places in the world for aquaculture and recreational fishing. The fish consumes a variety of animals: zooplankton, insects, amphipods, crayfish, gastropods and small bivalves. Tench will even occasionally feed on aquatic plants. It’s an extremely robust species, one that proliferates equally well in water that is high or low in oxygen, fresh or brackish, warm or cold, polluted or clean, flowing or stagnant, acidic or basic. It’s also a highly fertile and prolific species, which lends it enormous potential for ecological disruption.
A species that’s too prolific
The arrival of tench in Québec goes back to 1986 with specimens imported illegally from Germany. A few years later, in 1991, the fish was released unlawfully in the Richelieu River. The tench spread slowly during the first few years, but its abundance in the fisheries at Lake Saint Pierre has increased rapidly in recent years. One of the major local victims could be the copper redhorse (Moxostoma hubbsi), a species unique to Québec and designated threatened under the Québec Act respecting threatened or vulnerable species, and disappearing according to Canada’s Species at Risk Act. The Richelieu River is home to the only known copper redhorse breeding, spawning and juvenile growth sites.1
The tench is now spreading in the St. Lawrence River and its main tributaries, and comprises, according to Canadian researchers,2 a real invasion threat for the Great Lakes. Since 2001, tench observations have become more and more frequent and numerous in the St. Lawrence River corridor, especially in Lake Saint Pierre,3 where the perch population has collapsed and a moratorium on commercial and recreational perch fishing has been in effect since 2012. The presence of tench has been suggested as one of the many factors that may be contributing to delaying the perch recovery.4 The implementation of interventions designed to prevent or slow down the natural dispersal of this species is indispensable.
The Association des pêcheurs commerciaux du lac Saint-Pierre (APCLSP) and the Québec Ministère de la Faune, des Forêts et des Parcs (MFFP) as well as the Ministère de l’Agriculture des pêches et de l’alimentation (MAPAQ) are assessing the potential of commercial tench fishing as a management tool. The potential biomass of catches is estimated to be between 20 and 30 metric tons annually, according to the APCLSP. Tench flesh is white and good-tasting, but the product is difficult to launch on the food market because the skin is leathery and the flesh has a lot of bones. An alternative solution has been proposed, namely to use tench to feed the populations of fish and animals in zoos and aquariums. The Biodôme de Montréal has recently been collaborating on this project, and should be conducting tests with its residents that are already demonstrating a preference for fish (piscivorous species). In collaboration with the APCLSP and the MFFP, a first supply of 100 kilograms of frozen tench has been shipped to the Biodôme.
This pilot project could, if successful, support:
- managing the population of an invasive species,
- preserving a historical commercial fishing activity,
- using a local and untapped nutritional resource to feed the animal populations at the Biodôme de Montréal.
In collaboration with the MFFP and the APCLSP, this project will be under the supervision of a Biodôme team made up of veterinarians, animal technicians, aquatic collection workers and a research team in conservation physiology and aquaculture.
1 DFO (Fisheries and Oceans Canada). 2011. Advice relevant to the identification of the critical habitat for copper redhorse (Moxostoma hubbsi). Canadian Science Advisory Secretariat of DFO, Science Advisory Report 2010/072, Ottawa, 12 pp.
2Avlijas, S., A. Ricciardi, N. Mandrak. 2018.
Eurasian tench (Tinca tinca): the next Great Lakes invader. Canadian Journal of Fisheries and Aquatic Sciences. 75: 169-179.
3 Masson, S., Y. de Lafontaine, A.-M. Pelletier, G. Verreault, P. Brodeur, N. Vachon, H. Massé. 2013.
Dispersion récente de la tanche au Québec. Le Naturaliste Canadien. 137: 55-61.
4 Magnan, P., P. Brodeur, É. Paquin, N. Vachon, Y. Paradis, P. Dumont, T. Mailhot. 2017.
État du stock de perchaudes du lac Saint-Pierre en 2016. Comité scientifique sur la gestion de la perchaude du lac Saint-Pierre. Chaire de recherche du Canada en écologie des eaux douces, Université du Québec à Trois-Rivières and Ministère des Forêts, de la Faune et des Parcs. vi + 34 pp. + appendixes.