Scallops

Various species

Farm Siting

Scallops are a more sensitive species than others bivalves such as mussels and oysters in terms of their growing environment. Site selection for cultivating scallops is extremely important and factors include: substrate and/or depth of water; salinity; temperature; exposure to air, wind and currents; sedimentation rates; and food availability.

Buyers should seek assurances that all national and local laws are adhered to. All farms should have the required licences, permits and registrations in regards to their site and its operations accompanied by documentary evidence to demonstrate this compliance. Scallop operations may be managed to minimise site operations during peak sensitive periods or in times of low water quality episodes. Farm leases and permits can stipulate sustainable management practises.

In considering the environmental impacts of scallop aquaculture, it is important to view both the scale of the sector as well as the diversity of production systems1. The impacts of scallop aquaculture on the environment are often considered less than those of finfish and warm water prawn culture. Bivalves are considered keystone species in the ecosystem and therefore they can affect the surrounding environment in various ways2.

At all scales of bivalve production, the introduction the filtering bivalve molluscs and of physical on-growing structures to support them may produce changes in water movement and sediment dynamics that can affect both planktonic and seabed communities. However, the on-growing structures may also act as new habitat, and nursery areas for fish, crustaceans and molluscs3.

Operations associated with the growing and harvesting of scallops are relatively low impact in terms of activities that might lead to amenity and wildlife disturbance. One of the greatest potential impacts of cultivating filter feeders such as scallops is the net loss of energy (i.e. phytoplankton) from the ecosystem. Large monocultures, particularly in enclosed bays with limited water exchange, may exceed the carrying capacity (e.g. supplies of planktonic food) in that area and thus affect all aquatic organisms, including the farmed scallops themselves4, 5. Conversely, as scallops are primary consumers they can potentially mitigate impacts of nutrient enrichment (e.g. from land-based discharges and run-off), which can lead to eutrophication of coastal waters.

Coastal areas and estuaries where scallops are farmed are often sites of ecological and high amenity use, and therefore any large-scale cultivation may have impacts such as disturbing shore bird feeding sites, or on local navigation. Marine aquaculture operations may also have an aesthetic impact.

In many countries, siting a scallop farm would be restricted in areas with key biological or ecological functions. In the absence of such restrictions, the farmer should implement an environmental management plan to ensure no adverse effects on the ecological integrity of the area, and demonstrate there is no harm to threatened or endangered species and/or habitats. Best Management Plans (BMP’s), Codes of Good Practice6 often developed by industry groups, and certification are used as a means of preventing potentially unacceptable environmental interactions. Regarding the carrying capacity of the ecosystem and phytoplankton availability for other aquatic animals, farms should consider stocking appropriate densities.

Different countries regulate aquaculture and enforce policies differently, but often with the same goal of minimising environmental impact. Overall, the content of habitat regulations surrounding scallop culture takes into account environmental impacts and ecosystem services. Similarly, enforcement organisations should be identifiable, permitting and licensing process transparent and based on zoning or planning7 – although is not clear if such regulations in all locations are as effective or well-enforced8.

References

  1. Jeffery, K.R. et al., 2014. Background information for sustainable aquaculture development , addressing environmental protection in particular Sub-Title : Sustainable Aquaculture Development in the context of Water Framework Directive and Marine Strategy Framework, 2014 p156
  2. Gallardi, D., 2014. Effects of Bivalve Aquaculture on the Environment and Their Possible Mitigation: A Review. Fisheries and Aquaculture Journal, 5: 105
  3. Seafish
  4. Guo, X. and Luo, Y., 2016. Scallops and Scallop Aquaculture in China. Chapter 22 in Scallops: biology, ecology and aquaculture (Vol. 40)
  5. Bacher, C. et al, 2003. Modelling the effect of food depletion on scallop growth in Sungo Bay (China). Aquatic Living Resources, 16(1) p10-24
  6. ASSG
  7. FAO/World Bank
  8. Seafood Watch