Invasive Asian CarpOver Fishing

Each year, we harvest and consume more than one quarter of the annual fish production of oceans and tropical marine shelves. Of the approximately 1000 fish species in Canada, four species are thought to be globally extinct, two are no longer found in Canadian waters, and 49 are listed as endangered, threatened, or vulnerable as a result of over fishing. Over harvesting to this extent can greatly affect the biodiversity of many important aquatic ecosystems by causing a loss of genetic diversity as well as, a loss in the relative abundance of fish species; and has a direct impact on the food chain.

Invasive Species

Ontario's aquatic habitat and fish species are threatened by several invasive species including Asian carp, ZebraInvasive Purple Loosestrife mussels, Sea lampreys and Round gobies. Invasive aquatic plant species also cause ecological problems if they spread into new water bodies. They displace native vegetation, affect fish and wildlife habitat, and interfere with human uses of waterways. A few examples of invasive species in Ontario are the Eurasian water-milfoil, Purple loosestrife, European frog-bit, and Flowering rush.

How Invasive Species Spread

Ship ballast water- Ships take on water in special holding tanks, to balance their cargo. When they reach another port and load more cargo, they release their ballast. That ballast water mixes with the harbour water, bringing with it any organisms it contains. A single bulk cargo vessel in the Great Lakes can carry up to 20,000 tonnes of ballast water and contain several hundred different aquatic species.
Attached to ship’s hulls - Molluscs and other clinging organisms may attach themselves to a ship’s hull in one port, then either fall off into the water or are removed and dumped in the water during cleaning at another port. The construction and use of canals have provided an additional means for invasive species to enter water bodies.

Deliberate introduction for sport - Some sport fishers have illegally imported favoured species to a lake or river closer to their homes, in an attempt to establish a convenient fish stock for their personal recreation.

Unintentional introduction - Cultivated plants (originallyInvasive Eurasian Water-milfoil imported from other countries) sometimes spread to the wild; aquaculture and aquarium organisms may escape or be released by accident into local water bodies.

How Exotic Species Harm Rivers, Streams, and Lakes

Non-native species have earned their negative reputation as "invasive species" due to their successful rate of survival. A non-native animal may survive better than a native, not only because it has no natural enemies in the new environment, but because it grows more quickly or is better able to cope with unfavourable conditions than native species. This has the added effect of creating more competition for resources for native species.

Exotic plants tend to:

• Starve native plants of sunlight and nutrients;
• Crowd out native plants, jeopardising the animals dependent on them;
• Grow out of control, resulting in more organic matter in a water body which decays and causes the oxygen content of the water to become depleted, ultimately resulting in fish species loss;
• Obstruct navigation channels; and
• Clog machinery.

Exotic animals tend to:Invasive Zebra Mussels

• Consume food resources that native species need to survive;
• Occupy safe or supportive habitat, leaving a reduced amount of habitat for native species;
• Serve as food for native species but lack certain essential nutrients, leading to death of native offspring; and
• Consume eggs, young, and adults of native species.

Negative effects to society caused by exotic species include:

• High transportation and navigation costs;
• Reduced food availability for subsistence fishing;
• Reduced commercial fishing;
• Reduced sport fishing; and
• Reduced water quality or supply.

Adapted from US EPA: Threats to Aquatic Biodiversity and Environment Canada: Effects of Fishing on Biological Diversity in Canada