Concerns with Fishing - Version française à venir
Contaminant Accumulation in Fish
Child FishingThere are many naturally occurring substances that are found in our air, water and food, such as mercury, lead, copper, arsenic. At very low levels they pose no threat to the environment or human health. However, at elevated levels they can become harmful. The same is true for a number of human-made substances that have managed to find their way into our environment and into our food chain. When these substances enter the aquatic environment they can be absorbed by fish, directly from the water or in their food. If the substance is not excreted by the fish it can bioaccumulate, which is an increase in the concentration of a substance over time in a biological organism as a result of continued exposure. When the fish is caught either by larger fish, birds, or mammals the substances are passed on, and are considered to biomagnify or increase as they continue up the food chain.
Generally, high concentrations of persistent organic pollutants (POPs) that bioaccumulate are observed near large cities and industrialised areas. Aluminium, manganese, zinc, lead, mercury, and cadmium have also been found in high concentrations in benthic organisms, plants and fish.
Aquatic Ecosystem Loss And Reduced Water Quality
Healthy aquatic ecosystems are those where human disturbances have not impaired the natural functioning or significantly altered the structure of the system. An unhealthy aquatic ecosystem is one where the natural state is out of balance. Where there is an unbalance, species that depend on the ecosystem for habitat, nutrition and reproduction cycles may be threatened. Any loss of aquatic ecosystem or reduction in water quality can threaten fish populations in a number of ways.
| Threats to Fish and Fish Habitat | Problem |
| Sewage | Water that goes down the drain is full of waste that can be harmful to fish and to fish habitat. High organic and bacterial loads cause disease and reduce the amount of oxygen in the water. Chemicals and toxins can harm fish directly. |
| Urban Runoff< | Most rainwater that falls in cities flows into storm drains. Most storm drains empty directly into nearby lakes and rivers. Anything that gets washed down the storm drains ends up directly in fish habitats. |
| Garbage Dumps | Rainwater that washes through garbage dumps may flow into lakes and rivers, carrying toxins and garbage into fish habitat. |
| Farming | Application of too much fertilizer causes unnecessary runoff into waterways. Fertilizer causes excessive amounts of algae to grow. This throws off the balance of the ecosystem and only the most pollution-resistant fish will remain. |
| Pesticides | Herbicides are meant to kill weeds. Pesticides are designed to kill bugs. Both may actually be dangerous to fish. |
| Removal of sand or gravel from beaches, riverbanks or stream banks | The sand and gravel close to shorelines is an important part of fish habitat. E.g. salmon lay their eggs in gravel. |
| Riparian vegetation | Vegetation along shorelines may be removed to maximize land use, to provide access to the water, or sometimes just to improve the view. Plants along the shoreline do a lot to protect fish habitat. Without them, lots of good fish habitat may become degraded. |
| Destruction of shoreline | After clearing riparian vegetation, the banks are sometimes reinforced with walls to try and prevent erosion. The loss of very shallow water along the shore is a direct loss of fish habitat. Worse still, water flows faster along a hard wall. That means that there will be more erosion (and more loss of fish habitat) downstream from the wall. |
| Intakes for water supplies, cooling water and irrigation | Possibly the most important element of fish habitat is water. Removing water can lower water levels, causing shallow fish habitat areas to dry up. |
Invasive Species
Ontario's fish and the waters that support them are threatened by several exotic species that can be spread unknowingly by anglers and boaters. Some of the harmful exotic species that have been discovered in Ontario waters and ways of preventing their spread are described below. Whenever you move your boat from one water body to another, exotic species may tag along for the ride.
Types of Invasive Species In Ontario
Zebra mussels: The barnacle-like zebra mussel poses a multibillion dollar threat to North America's industrial, agricultural, and municipal water supplies. It could also become a costly nuisance for freshwater shipping, fishing, and shellfish harvesting well. The zebra mussel was first found in the Great Lakes in 1988, and it is invading other waters. You can help prevent it from becoming more widespread and invading other inland lakes and rivers by flushing your engine and by ensuring that hull, machinery and bait-wells are free of zebra mussels.
Other examples of invasive species are Ruffe, Round Goby, Smelt, Crayfish, Grass Carp, and Spiny Water Flea. To learn more about these invasive species go to the Canadian Wildlife Federation Invasive Species in Canada Database<.
There are also invasive aquatic plant species. Several species of exotic aquatic plants found in Ontario can cause ecological problems if they spread into new water bodies. Eurasian water-milfoil, purple loosestrife, European frog-bit, and flowering rush are just a few examples of these types of plants. They can displace native vegetation, affect fish and wildlife habitat, and interfere with human uses of waterways. Aquatic plants can also harbour zebra mussels and other species.
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 (originally imported from other countries) sometimes spread to the wild; aquaculture and aquarium organisms may escape or be released by accident into local water bodies.
There are some important things you can do to prevent the transport of harmful exotic species from one lake or river to another:
- Inspect your boat, motor, trailer, and boating equipment (anchor, centreboards, rollers, axles) and remove any zebra mussels and other animals and plants that are visible before leaving any waterbody;
- Drain water from the motor, livewell, bilge and transom wells while on land before leaving the waterbody
- Wash/dry your boat, tackle, downriggers, trailer, and other boating equipment to kill harmful species that were not visible at the boat launch. Some aquatic nuisance species can survive more than 2 weeks out of water so it is important to:
o rinse your boat and equipment that normally gets wet with hot tap water (greater than 40ºC); or
o spray your boat and trailer with high pressure water (250 psi); or
o dry your boat and equipment for at least 5 days before transporting to another water body.
- Empty your bait bucket on land before leaving any water body. Never release live bait into a water body, or release aquatic animals from one water body into another;
- Learn how to identify zebra mussels and other exotic species. If you suspect a new infestation report it to the Ministry of Natural Resources or the Invading Species Hotline (1-800-563-7711) - this hotline is a partnership between the Ontario Ministry of Natural Resources and the Ontario Federation of Anglers and Hunters.