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Impacts of Aquaculture

As the Irish marine aquaculture industry continues to grow, so do the ecological, human health and animal welfare problems associated with the sector. The fact that marine aquaculture — the aquatic version of industrial agriculture — takes place in coastal waters, where biodiversity is high and pressures from multiple interacting human activities are increasing, both complicates and amplifies the potential environmental impacts of the sector.

All forms of mariculture, regardless of physical structure or economic motivation, affect biodiversity at genetic, species and ecosystem levels. At the ecosystem level, both goods and services functions can be affected, with widespread consequences and knock-on long-term effects. Therefore, the interconnected nature of aquatic communities require that impacts on aquatic ecosystems should be considered in a holistic manner, both in the short and long terms.

Secretariat of the Convention on Biological Diversity (2004)

An integrated ecosystem-based approach has yet to be applied to the management of marine aquaculture in Ireland. Most environmental impact studies have been conducted at project development (i.e. single fish farm) level. Whereas the local scale effects are well documented, the effects at the ecosystem or regional scale remain largely unknown. The different sensitivities of different ecosystems to potential impacts, and the different capacities of different ecosystems to absorb changes resulting from aquaculture activities mean that assessing the potential cumulative impacts of marine aquaculture at ecosystem level is difficult. Nevertheless, a strategic environmental assessment of the marine aquaculture sector is a long overdue, vital first step towards integrating marine aquaculture into the overall process of integrated coastal zone management (ICZM).

Key concerns
General conclusions about the impacts of marine aquaculture cannot easily be drawn because the impacts depend on the finfish and shellfish species, culture methods, stocking densities, feed types, site hydrographic properties, operational and management practices, and other variables involved. However, key environmental concerns include:

• Accumulation of organic waste (fish faeces and uneaten fish feed) and mass mortalities resulting in localised but profound water quality deterioration and changes to benthic (seabed) communities, biodiversity and nutrient balances.

• Introduction and spread of diseases and parasites from farmed fish to wild populations and vice versa.

• Chemical usage, including antibiotics and other chemotherapeutants used to prevent and treat diseases and parasites in farmed fish, and pesticides (antifoulants) used to prevent biofouling of net cages and other submerged structures, leading to toxicity and bioaccumulation of persistent chemical residues in the food chain.
  
  
• Accidental introductions (escapees) from fish farms, including of non-indigenous (also called new, novel, exotic or alien) species and strains and genetically modified (transgenic) fish, and subsequent interbreeding and transfer of undesirable genetic traits to wild populations.
  
  
• Ecological interactions between marine aquaculture operations and co-occurring wild species, including protected bird species, seals and other predators.
  
  
• The use of "industrial fishing" to provide large quantities of often contaminated fish feed for farmed fish, and the net loss of protein in the global food supply because it takes between 2.5-5kg of wild fish to grow 1kg of farmed salmon.
  
  
• The welfare of intensively farmed fish, which has implications for human health.
  
  
• Spatial conflicts with other sea and coastal resource user groups, such as fisheries, offshore wind farming, angling and tourism interests.

Reference

Secretariat of the Convention on Biological Diversity. 2004. Solutions for sustainable mariculture - avoiding the adverse effects of mariculture on biological diversity. CBD Technical Series No.12.