Alteration of habitat
Installation of infrastructure and the ongoing operation of aquaculture facilities can result in physical alteration to fish habitat through the use of equipment or with the placement of physical structures in the water or on the sea or lake-bed (benthos). These types of activities can sometimes result in ecological impacts in the water or on the benthos.
Habitat structure is altered when marine finfish and shellfish aquaculture facilities add physical infrastructure to aquatic environments. Ropes, floats, trays, net structures and anchors provide surfaces upon which planktonic larvae and bio-fouling organisms may settle and may also attract mobile species, creating artificial reefs. Anchors may alter or create benthic habitat in small localized areas. Larger structures (e.g., net-pen or long-line systems) can have localized impacts on water currents and may shade the sea or lake bed in shallow waters. The addition of structures to support on-bottom shellfish culture may increase siltation in the immediate vicinity, raise concentrations of organic matter around the structures, and act as a surface for algae growth and for settlement of aquatic animals. In addition, maintenance activities such as net cleaning, harvesting techniques, the use of vehicles and mechanized equipment, and increased foot traffic in and around on-bottom shellfish sites, may affect sediments in the areas where these activities are carried out, although generally these effects are localized and temporary.
Aquaculture operators may also use treatments such as antifoulant coatings, pressure washing, lime, vinegar (acetic acid) and brine, to remove organisms that settle on boats, nets and equipment. Managing biofouling levels helps to maintain a healthy water flow for fish and also maintain the integrity of containment systems (e.g., nets, system moorings, long lines, etc.). Antifoulant products used in Canada are regulated under the Pest Control Products Act, and any product with a Pest Control Product Registration Number must be used in accordance with label conditions, and reported annually as a requirement of the Aquaculture Activities Regulations.
Some aquaculture operators use underwater lighting at marine finfish aquaculture sites to delay the onset of spawning maturity. This improves feeding behaviour, growth rates and the quality of fish flesh. Lights are used at night within net cages from autumn to spring, when there are fewer hours of daylight. Research indicates that lights do not penetrate more than a few metres beyond marine nets, suggesting that their use has minimal effect on the surrounding environment. However, it is possible that lights may influence the behaviour of wild fish by attracting them to—or causing them to avoid—farm sites.
In British Columbia (BC), farm operators must record the type, intensity and number of lights used at their facilities, as well as the period of day and season they are used, as part of their Conditions of Licence. This information is submitted to DFO annually and allows aquaculture management staff to further assess the potential impacts of light use and to develop appropriate management measures, if required.
The impact of aquaculture infrastructure is determined by the extent, intensity, timing and location of the disruption to habitat. These factors are considered by Canadian aquaculture regulators when reviewing lease or licence applications for new aquaculture facilities. Only those locations that present minimal risk to fish or fish habitat are approved. In addition, where effects may be more severe on a seasonal basis, regulators may put measures in place to restrict the duration, timing or extent of aquaculture activities.
The Aquaculture Activities Regulations require that licence holders put in place measures to minimize serious harm to fish and fish habitat. Descriptions of measures taken form part of each licence holder’s annual report to DFO.
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