Environmental Impacts & Mitigation

Fish Aquaculture @TNC

Understanding and addressing environmental impacts of finfish aquaculture in sensitive coral reef areas is essential for coral reef managers. The four major categories of environmental impacts are:

  • Impacts to wild stocks
  • Impacts to habitat
  • Water pollution
  • Disease

These four interrelated impacts can generally be addressed and mitigated through appropriate species selection, gear type, technology use, regulations that support sustainable management, environmental impact assessment, site selection and spatial planning approaches. ref Each of these impacts should be thoroughly discussed and researched during project planning and management to minimize risks. Key environmental impacts and mitigation strategies are described in detail below and can also be downloaded opens in a new windowhereopens PDF file .

Standard operating procedures for each farm should be implemented to provide a consistent and safeguarded system to minimize risk and maximize mitigation strategies. Additionally, information and knowledge regarding sustainable management regulations, siting, spatial planning, and area management are important for successfully managing an aquaculture farm in nearshore reef systems.

Impacts to Wild Stocks

One of the main impacts aquaculture can have on wild stocks is the continuous extraction of fry from the ecosystem. If extraction is unsustainable, the reproductive potential of species being removed will be negatively affected by not allowing enough fish to reach sexual maturity and spawn. Also, fish escapements can occur when the cage nets are not serviced properly and holes form, or due to poor practices during stocking, harvesting, or transfer of fish. Farmed fish can be released into the wild and potentially impact wild stocks by introducing diseases and diluting the genetic pool through interbreeding with wild populations. If proper maintenance and planning are carried out, holes in nets and fish escapements can be prevented. ref Additionally, if properly managed and impacts are minimized, cages in coastal waters can become fish aggregating devices (FADs) and potentially provide habitat value.

Impacts to Habitat

The installation and operation of finfish cages in coastal areas can have both direct and indirect impacts on habitat. Direct impacts can be in the form of displacement or removal of habitats to make space for infrastructure for the cages, such as cutting mangroves for the construction of a dock or pier, or damage to corals and seagrass beds during the installation of cage anchors and weights. Proper farm siting needs to take place before the construction and installation of the cage to determine the optimal location while taking into account currents, tides, seafloor depth, and distance to sensitive habitats like coral reefs, mangroves, and seagrass beds. Indirect impacts to local habitats include damage to benthic communities and declining water quality from overfeeding. Proper feeding practices can help to mitigate these impacts. ref

Water Pollution

Water quality in the surrounding area of the cage must be considered and monitored. Stocking and maintaining too many fish in a small space can lower the overall water quality by depleting oxygen levels and increasing nitrogen, phosphorus, and ammonia levels, which if allowed to pass a level that the environment cannot absorb or diffuse, can cause detrimental effects to the local area. Careful and diligent monitoring needs to take place before and after the cage has been installed to determine if nutrient build up is occurring at the site.

Disease

Like any other food production system, if too many animals are kept in a relatively small space and not given optimal conditions for health and growth, there can be outbreaks of diseases and parasites. Proper management needs to take into account stocking density, fast currents to flush clean water in and waste out, high feed quality, standardized feeding protocols, and overall monitoring of fish behavior and health. As soon as fish begin displaying certain behavioral or physical traits that may indicate disease or parasites, correct and appropriate treatments need to take place in order to minimize mortalities. ref

The next sections describe the four major categories of environmental impacts in detail.

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