The impact of physical barriers on Atlantics Salmon

The Atlantic Salmon Salmo salar is native to the basin of the North Atlantic Ocean (DFO 1). “ In Canada, the Atlantic Salmon occurs naturally throughout Newfoundland, Labrador, the Maritime Provinces, eastern Quebec and the Ungava region of northern Quebec” (DFO1). The Atlantic Salmon is an anadromous fish. Anadromous fishes are those fishes that go against the rivers current to tributaries in spawning grounds. “Any physical barrier such as dam, culvert, waterfall can block or hinder upstream migration” (2). Their affects may result in less number of spawning fish reach to tributaries and changing in gene pool.

School of Atlantic Salmon
D. Danvoye (DFO 1)
Marine Atlantic Salmon and landlocked salmon return from sea and lake to tributaries respectively. They spawn in October and November in Canada (DFO 1). It takes about 110 days to hatch and young salmon stay 2-8 years in rivers depending on region feeding on aquatic insect larvae (DFO 1). “Atlantic Salmon have a high degree of fidelity to their natal rivers” (DFO1).
Department Fish and Ocean (DFO 1)
“The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has identified 16 designatables units (DU) of Atlantic Salmon, 11 of which are considered at risk” (DFO1). Until March 1, 2013, Fisheries and Oceans Canada was in consultation about the addition of five atlantic salmon populations to the List of Wildlife Species at Risk under the Species at Risk Act (SARA) (DFO1). ‘The Atlantic Salmon commercial fishery was closed progressively in Canadian waters from the mid-1980s until the complete closure in 2000” (DFO1).
There are several possible causes for population decline of atlantic salmon. Climatic changes, fishing, and obstacles in fresh water such as dams are some important factor for this decline (DFO1). Under the Canadian Federal Inclusion List Regulation, activities, even if they are not related to construction of a physical infrastructure but result in the destruction of fish and fish habitat needs EIA (Noble 2010). Salmon habitat is protected under the fish habitat protection provisions of the Fisheries Act (DFO1).
A possible mitigation mechanism for facilitating natural upstream migration of Atlantic Salmon is constructing fishways at dams and other physical barriers which may block or hinder their migration. A fishway is a canal that diverts an appropriate quantity of water from upper part of a barrier to the lower part. The depth and velocity of water are very important points that must take in to consideration in planning of a fishway.
Here is an example of a fishway

As an example for homologous fish, the Amir Kabir dam in Iran blocked the migration of Caspian salmon, (Salmo trutta caspius Kessler, 1877). At that time, no EIA was required for the construction. Many years after the construction, Iranian Fisheries Organization built several hatcheries and still are spending huge amount of money in hatcheries to restock Caspian salmon as well as sturgeon fishes every year for the same reason.
1- 04/10/2013
2- 04/10/2013
3- Noble B.F. 2010. Introduction to environmental Impact Assessment, Oxford University Press Second edition p74.


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