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Managing organic wastes

During aquaculture operations, organic material such as unconsumed feed, fecal matter, shellfish drop-off, and other organisms and materials are released into the surrounding waters and can accumulate on the sea or lake bed. This organic matter (referred to as biochemical oxygen-demanding or BOD matter) is utilized by organisms, but if enough accumulates, the decomposition process begins to use oxygen and change the chemical properties of the nearby sediment. If sufficient material accumulates, the biodiversity in local benthic habitats may be decreased, either by smothering or due to the chemical changes and lack of oxygen. Minimizing the accumulation of BOD matter and monitoring the benthic zone to measure and restrict impact are critical components of sustainable aquaculture management for marine net-pen operations.

The extent of benthic impacts around finfish facilities are monitored using established methods. For finfish farms located over muddy or soft sediments, a sample of this sediment is taken and the amount of free sulfide is measured – this is used as an indicator of oxygen in the sediment which is an indicator of the type of organisms that can survive in the sediment (i.e., the biodiversity). When it is not possible to obtain sediment samples (e.g., from “hard-bottom sites”), visual monitoring for the presence of Beggiatoa species (or similar bacteria) or marine worms (e.g., class Polychaeta) are used as biomarkers of aquaculture impact.

Scientific research to characterize the effect of the impact from organic wastes on the ecosystem, protocols for measuring these impacts and the development and evaluation of additional indicators of sediment state and biodiversity is on-going. This research and scientific advice will inform the need for future regulatory amendments.

The Aquaculture Activities Regulations require operators of marine finfish farms to report on the results of benthic monitoring, by providing either free sulfide or visual data, depending on their conditions, according to monitoring standards developed by Fisheries and Oceans Canada (DFO). These standards require operators to take samples at each facility 30 days prior to or after the predicted maximum daily quantity of feed usage or peak biomass. Samples or video must be taken at least once during the production cycle at sea, or every 24 months for farms with finfish continuously on site. If the thresholds set by the Regulations are exceeded, DFO must be notified within 14 days after the samples or video have been taken, and facilities cannot be re-stocked until regulatory thresholds have been reached.

As the regulator of the aquaculture industry in British Columbia (BC), DFO monitors and assesses benthic impacts and the effects of fish farms on the environment. Its benthic monitoring program is designed to limit the location, area, and intensity of impact created by fish farms to the seabed and to support sustainable aquaculture by maintaining healthy ecosystems.  In addition, the Department assesses siting proposals for new marine finfish farms to manage benthic impact away from sensitive or critical species and habitats, such as eelgrass beds, shellfish beds, glass sponge reefs and juvenile rockfish nurseries.

DFO biologists in BC and provincial biologists in coastal provinces conduct field audits to collect and assess sediment samples and video data, and also “office audits” of video data submitted by industry. These audits allow staff to monitor environmental performance of active sites, provide valuable insight into benthic impacts during different times of the production and the site recovery cycle, while corroborating and generating further confidence in industry-reported data.


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