Dredging and biosecurity risks

Dredging activities present biosecurity risks associated with the introduction and spread of aquatic pests and 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'.

Aquatic pests and diseases

Aquatic pests are a significant threat to South Australia's fisheries, aquaculture, recreation and tourism industries. They can also pose risks to:

• public health
• aquatic amenity
• environmental values
• biodiversity.

Aquatic animals can be infected by diseases that are caused by pathogens, such as viruses, bacteria, fungi, protozoa and parasites. Aquatic animal diseases impact the:

• sustainability and health of commercial and recreational fisheries
• productivity of aquaculture industries
• access to markets for seafood industries
• aquatic environments.

Some aquatic diseases are spread or introduced by biofouling.

Biosecurity risks to SA waters

There are aquatic pests established within certain areas of SA, such as these listed noxious species:

• European fan worm (Sabella spanzanii)
• European green crab (Carcinus maenas)
• Codium fragile spp. Tomentosoides
• Caulerpa taxifolia
• Vase tunicate (Ciona intestinalis).

Additionally, there are aquatic pests established interstate and overseas that pose a risk to SA waters.

Legislative requirements

Dredging activities must comply with both the:

• Fisheries Management Act 2007
• Livestock Act 1997.

Additionally, please refer to the South Australian EPA Dredging Guideline.

The Fisheries Management Act 2007 provides for the control of exotic and noxious aquatic organisms, commonly referred to as aquatic pests. Under the Act:

• the release or deposit of exotic species into any waters (unless permitted by the Minister) is prohibited
• noxious species are not allowed to be possessed by individuals or released into state waters (unless permitted by the Minister).

The Livestock Act 1997 provides for the management of notifiable diseases, including aquatic diseases such as Pacific Oyster Mortality Syndrome (POMS). Under this Act, 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.

Consult before dredging

Consult PIRSA for information on biosecurity risks in the proposed dredging area. PIRSA will advise of risks such as the release of:

• viable fragments of aquatic pests or disease
• algal cysts which can cause a toxic algal bloom.

PIRSA can also assist with a risk assessment of the impact on fisheries and aquaculture production in the area.

Risk assessments

To make sure aquatic pests and diseases are not spread by biofouling, dredge discharges, or spoil, a risk assessment should consider the:

• vessels
• equipment
• practices used
• risks associated with the dredge site.

Translocation factors influence the risk of particular vessels and dredging practices. These include:

1. timing/frequency of the cleaning, antifouling, and inspections of vessels and equipment used
2. vessel internal seawater systems, niche areas, and their treatment and inspection regime
3. the operation and hull design profiles –
   • the longer a wetted surface remains stationary or moving slower than 5 knots in port, at the dredge site, in coastal waters, or on longer slow voyages such as towing; the more likely it is to accumulate biofouling, and for any aquatic pests to survive
   • if the departure and arrival properties are similar (water temperature range, salinity, water depth, habitat range or substrate types), there is higher risk of aquatic pest establishment from one area to the other
   • consider opportunities for the equipment to be removed from the water and thoroughly dried between use in different areas or regions
4. the antifoulant used and its suitability for the vessel operation and profile
5. damage to antifoulant coatings in some locations because of work activities
6. surfaces, components and fittings not treated with antifoulant coatings due to operating and material requirements
7. removal and capture of mud, sediments and biofouling in dredge equipment and ancillary fittings
8. which mitigation measures are in place and their effectiveness.

Manage biofouling

Biofouling is the accumulation of aquatic organisms (micro-organisms, plants and animals) on surfaces and structures that are immersed in, or exposed to, the aquatic environment. Surfaces include:

• vessel hulls
• niche areas such as sea chests and internal water systems.

Support vessels and equipment associated with dredging, particularly those remaining in water for extended periods, need management to minimise the risks of biofouling. Vessels and equipment undertaking the works 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
• record books in place to prevent the spread of pests and diseases.

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.

Information about biofouling and ballast water advice for vessel owners.

Management plans

Use the following resources 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
• manage in-water equipment to minimise biofouling –
  • Decontamination advice for POMS fact sheet (PDF 115.7 KB)
  • Cleaning marine equipment fact sheet (PDF 175.7 KB)
• keep a record book for each vessel, capturing significant dates and actions outlined in the management plan, such as hull inspections and cleaning.

Existing containment areas

POMS

An outbreak of 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.