Overview of the aquaculture Pathways of Effects tool for assessing aquaculture impacts
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A Pathways of Effects (PoE) model is a tool that conveys complex interactions between human activities, the type of cause-effect relationships that are known to exist, and the mechanisms by which stressors ultimately lead to effects in the aquatic environment. The model recognizes that a single environmental stressor can have multiple source activities and can lead to one or more environmental effects. It also recognizes that a single environmental effect can be influenced by one or more stressors or activities. In considering a specific activity, it is important that site specific attributes and anticipated ecosystem changes (in addition to specific aquaculture stressors), like climate change, be incorporated into the assessment of effects and the evaluation of the efficacy of potential mitigation measures.
Fisheries and Oceans (DFO) Fisheries Protection Program (FPP) uses Pathways of Effects models in evaluating projects. Consistent with this approach, fish and fish habitat impact evaluation of new aquaculture sites by DFO consider the range of activities, associated stressors and the effects of these stressors on different components of the ecosystem.
In making decisions around aquaculture activities, following the Framework for Aquaculture Risk Management (FARM), the Aquaculture Pathways of Effects are used to identify issues for scientific assessment and advice, and support the risk management steps of identifying mitigation options, the selection of risk management strategies and the determination of the residual risk after the application of mitigation measures.
Aquaculture Pathways of Effects
The Aquaculture Pathways of Effects model (Figure 1) was developed collaboratively with Provincial and Territorial regulators. A Canadian Science Advisory Secretariat (CSAS) process confirmed the scientific basis for the linkages between the following major stressor categories associated with aquaculture activities, the resulting stressors that can result, and the potential effects of these stressors on different ecosystem and environmental componentsFootnote 1.
As additional data from monitoring around aquaculture sites and new scientific research results becomes available, the characterization of the duration, scale and intensity of the stressor-effects relationships will need to be reviewed and updated to reflect this new information.
At the point of evaluating a specific aquaculture application, the linkages between each of the stressors and the relevant effects described in the Aquaculture Pathways of Effects Tool are considered. The specific environment and activity will determine which stressor-effect linkages exist, and what mitigation measures can be used to effectively and sustainably “break” or lessen the stressor-effect linkages. The residual risks to each of the environmental components from the aquaculture activities following the application of mitigation measures, are then considered in the Risk Management Strategy.
Physical alterations to the habitat occurs during the placement or removal of physical infrastructure (e.g., net pens, longlines, rafts, anchors and moorings, shellfish beach culture structures), as well as during the use of husbandry equipment (e.g., underwater lights to increase growth in marine finfish or acoustic deterrent devices to discourage predators Footnote 2).
The extent and impact of the predicted physical alterations to habitat are considered primarily during the pre-operational stage (e.g., site application), which includes an evaluation of the type of benthic habitat in the area being proposed for aquaculture.
Release of chemicals and debris occurs primarily with activities associated with site and stock management, and the use of operational equipment where chemicals and debris may be released. Examples include the use of authorized pesticides, drugs and antifouling agents, and the use of materials in construction (e.g., steel, wood, floatation) and operations (e.g., feed bags, ropes), which can be lost from sites as debris.
The effect of the use of pesticides, drugs and antifoulants on the receiving environment, including on non-target organisms, is assessed by Health Canada.
DFO and it’s regulatory partners (HC and ECCC) are working collaboratively to develop an assessment tool for determining post-deposit monitoring for drugs or pesticides. Once implemented, the initial assessment will occur at the pre-operational stage and results from any post-deposit monitoring will inform future requirements for on-going monitoring.
Release of organic and related matter occurs as a result of stock management activities (e.g., the feeding and cultivation of fish, removal or natural sloughing of biofouling organisms from physical infrastructure) that have an organic or related component (e.g., nutrients).
The predicted extent of organic deposition on the surrounding seafloor is assessed at the pre-operational stage. As part of the on-going operational compliance under the Aquaculture Activities Regulations, marine finfish aquaculture operations must meet a performance-based regulatory requirement related to the release of organic matter. Similar regulatory standards could also be applicable to freshwater finfish and shellfish operations in the future.
Removal of nutrients and organic matter occurs as a result of stock management activities where some cultured species (e.g., bivalves) remove particulate matter, nutrients and oxygen from the water column.
The predicted extent of the removal of nutrients by the addition of cultured shellfish and the predicted effects on wild populations is assessed at the pre-operational stage.
Release or removal of fish occurs primarily as a result of stock management activities.
The removal of fish is considered and managed under DFO’s bycatch policyFootnote 3. This occurs when some individual wild fish may be temporarily or permanently removed from waters along with cultured fish (e.g., during grading or at harvest), or as part of biofouling or predator control.
The addition of fish to the environment occurs either as a result of intentional stocking of cultured fish into aquatic environments for cultivation (e.g., salmon enhancement), or as a result of unintentional release of fish (e.g., escapes).
The impact on wild populations from the unintentional release of cultured organisms is currently considered at the pre-operational stage, and is linked to fiduciary responsibilities associated with the Species at Risk Act and the Fisheries Act. It is also considered by the Introductions and Transfers Committee in the assessment of requests for non-routine introductions or transfers, under the s.56c of the Fishery (General) Regulations.
Release of pathogens and pests is associated with site and stock management. The increase in biomass of fish within an area due to an aquaculture site can influence the presence or abundance of fish pathogens (e.g., bacteria, viruses) and pests (e.g., sea lice and tunicates).
The introduction of pathogens or pests is evaluated at the operational stage, primarily by the Introductions and Transfers Committees (ITC). Conditions of licence (either provincial, territorial, or federal) outline mitigation measures for the management of the abundance of pathogens or pests.
Notifiable diseases are regulated by the Canadian Food Inspection Agency.
Information and examples of how the Aquaculture Pathways of Effects Tool can be used to support aquaculture decisions within the Framework for Aquaculture Risk Management can be found in the associated document Framework for Aquaculture Risk Management: Application of the Aquaculture Pathways of Effects in Aquaculture Activities Decisions.
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