Dredging and biosecurity risks
Dredging activities present the biosecurity risks of introducing aquatic pests and aquatic diseases.
The Environment Protection Authority (EPA) defines dredging as: 'removing solid matter from the bed of any marine waters or inland waters by any digging or suction apparatus, but excluding works carried out for the establishment of a visual aid to navigation and any lawful fishing or recreational activity'.
Dredging activities must comply with state legislation and the EPA Dredging Guideline to minimise the potential for environmental harm.
Legislative requirements
The Fisheries Management Act 2007 outlines the control measures for aquatic pest organisms. Unless permitted by the Minister, it is prohibited to:
- release or deposit exotic species into any waters
- possess noxious species or release them into state waters.
The Livestock Act 1997 manages notifiable diseases, including aquatic diseases. It specifies that a person must not:
- undertake an act where livestock become affected or further affected with a notifiable condition
- bring a notifiable disease to the state without the approval of the Chief Inspector.
Dredging consultation
Before dredging, make sure aquatic pests and diseases will not be spread by biofouling, dredge discharges, or spoil – consider factors such as the vessels, equipment, and practices used, and risks associated with the dredge site or translocation.
Consult PIRSA for information on biosecurity risks in the proposed dredging area. We will advise about the release of aquatic pests or viable fragments of disease, including algal cysts which can cause a toxic algal bloom.
We can also assist with a risk assessment of the impact on fisheries and aquaculture production in the area.
Risk assessment
Consider the following to determine your biosecurity risk:
- Timing and frequency of cleaning, antifouling, and inspections of vessels and equipment used. Take opportunities to remove the equipment from the water and thoroughly dry it between use in different areas or regions.
- Vessel internal seawater systems, niche areas, and their treatment and inspection regime.
- Operation and hull design profiles:
- a wetted surface is more likely to accumulate biofouling with live aquatic pests when it remains stationary or moves slower than 5 knots in port at the dredge site, is in coastal waters, or is on longer slow voyages such as towing
- there is higher risk of aquatic pest establishment from one area to another if the departure and arrival properties are similar – water temperature range, salinity, water depth, habitat range or substrate types.
- The antifoulant used, including:
- its suitability for the vessel operation and profile
- any damage to antifoulant coatings because of work activities
- surfaces, components, and fittings not treated with antifoulant coatings due to operating and material requirements.
- Removal and capture of mud, sediments, and biofouling in dredge equipment and ancillary fittings.
- The mitigation measures in place and their effectiveness.
Manage biofouling
Biofouling is the accumulation of aquatic micro-organisms, plants and animals on surfaces and structures that are immersed in, or exposed to, the aquatic environment. This can include vessel hulls, niche areas such as sea chests, and internal water systems.
Support vessels and equipment associated with dredging, especially those staying in water for extended periods, must be managed to minimise biofouling. They should be cleaned before and after dredging, and before moving to a new region.
Dredge proponents should make sure vessels and equipment have:
- An effective biofouling management plan to prevent the spread of pests and diseases.
- Record books for each vessel capturing significant dates and actions outlined in the management plan, such as hull inspections and cleaning.
This is consistent with the International Maritime Organization (IMO) guidelines and the national biofouling guidelines. It should be considered in any contractual arrangements with dredge contractors.
Find out more about biofouling and ballast water advice for vessel owners.
Management plan resources
Use the following information to create management plans:
- National biofouling management guidelines for non-trading vessels (PDF) – includes dredge and support vessels
- National biofouling management guidelines for commercial vessels (PDF)
- IMO guidelines for biofouling – includes template for biofouling management plan and record book
- Decontamination advice for POMS factsheet () – manage in-water equipment
- Cleaning marine equipment factsheet ()
Aquatic pests and diseases of concern
There are aquatic pests interstate and overseas that have potential to spread to SA waters through dredging or biofouling.
Some noxious species are already established in certain areas of our state and must be managed, including:
- European Fan Worm (Sabella spanzanii)
- European Green Crab (Carcinus maenas)
- Codium fragile spp. Tomentosoides
- Caulerpa taxifolia
- Vase Tunicate (Ciona intestinalis).
The following aquatic organisms have caused existing containment areas.
POMS
An outbreak of Pacific Oyster Mortality Syndrome (POMS) was identified in the Port River through routine research in 2018. The virus is now endemic in the Port River and is a major concern for the Pacific oyster aquaculture industry. It has not yet been detected in SA commercial oyster farming areas.
The Port River now has restrictions on the removal of bivalves from the area to contain the virus to the Port River. See Port River POMS outbreak in feral oysters.
Caulerpa
Caulerpa taxifolia is established in the Port River-Barker Inlet system and cannot be eradicated.
While this alga does not grow well in exposed gulf waters, it could become established along the nearshore environments, particularly among degraded seagrasses on the metropolitan coast and north to Port Gawler.
A containment area covering all waters of the Port River-Barker Inlet system was declared in 2010, to limit its spread.
Contact
For advice on where aquatic pests or diseases are established, and mitigation measures for dredging activities, contact PIRSA’s Aquatic Pests team:
Phone: (08) 8303 9620
Email: pirsa.invasivespecies@sa.gov.au
Report suspected exotic species and diseases
Early detection is important to stop the establishment and spread of aquatic pests and diseases.
Report unusual sightings immediately, including mass fish die-off.