Sediments and aquaculture
How can aquaculture activities influence sediments in waterways?
Commercial aquaculture incorporates large structures like fish cages and oyster racks that create obstructions in the water column that can alter currents and water flow. These structures may affect the way sediments deposit and accumulate. Aquaculture structures should be designed and positioned to minimise their effects on water flow and on sediment movement and re-suspension.
Alternatively, when soils erode, sediments are washed into streams, rivers, and estuaries from the land. These sediments can significantly alter and degrade habitat relied upon by customary aquaculture species, such as shellfish.
Potential impacts of sediment on water quality and mahinga kai
- Decreased water clarity - increased sediment loading into a waterbody will decrease water clarity and reduce visibility for fish seeking food.
- Damage to fish gills and filter feeding apparatus of invertebrates.
- Changes to the benthic (bottom) structure of an estuary or stream, as substrates are replaced/smothered by mud and silt.
- Decreased numbers of invertebrate species from smothering of habitat (e.g., shellfish). Diverse invertebrate communities are also an indicator of healthy ecosystems.
- Decreased algal food supply at base of food chain – sediments can scour algae from rocks, make algae unpalatable, or reduce light to levels where algae cannot grow, because plants need light to photosynthesise.
- Increased contaminants from surrounding land - sediments can transport attached pollutants such as nutrients, bacteria and toxic chemicals from the land into estuaries and streams.
