Preventing the Introduction of Invasive Species

Historically the most prolific vector of translocation was hull fouling, whereby organisms attached themselves to the hulls of ships at one location and were carried across oceanographic boundaries during the voyage either falling off naturally in a new habitat or by the cleaning of the ships hull. The discharge of alien species in ships ballast water has over the last century increasingly become a dominant vector for such introductions.

The environmental consequences can be severe. The best known and recorded examples are probably the zebra mussel introduction into US waters and the comb jelly fish into the Black Sea. Apart from the damage to indigenous aquatic biodiversity, the social and economic impacts can be massive.

Ballast water from large vessels is thought to be the main source of international introductions of harmful invasive aquatic species. However, recreational craft are now thought to be significant secondary vectors for their spread after an initial introduction.

The spread of the golden mussel throughout the waters of Brazil has a small boat vector, together with the zebra mussel in Ireland and to Cardiff Bay. Now the Japanese seaweed Undaria has become endemic in Venice Lagoon.  Ballast water and hull fouling are thought to be the likely vectors.

All species which are non-indigenous to a discrete eco-system are potentially harmful, both to biodiversity and to social and economic interests. Therefore precautionary action is essential to limit the spread of alien species by small recreational and other craft.

The recent meeting of the UNEP Commission on Biological Diversity in its final declaration stated under Marine biofouling, particularly hull-fouling:-

"Encourages Parties and other governments to implement controls at national level, for example through appropriate measures (eg., regulations and standards), on marine biofouling as a pathway for the introduction and spread of invasive alien species, including recreational vessels."

In addition to hull fouling, anchors and anchor chains may have alien species attached, especially if clogged with mud. Water intakes, cockpit drain tubes and bow thruster housings etc. are also discrete locations for fouling. Bilge water may also contain alien species, especially as larvae, eggs or cysts in the case of algae.

As small craft are not embraced by the merchant shipping act, voluntary action is the traditional way to implement a management strategy for recreational craft. The following gives some guidance on such action.

Code of practice to minimise and ultimately prevent the spread of harmful alien invasive aquatic species by recreational and other small boats.

1. Boats sailing in marine waters

• The most important preventative action that can be taken is one that boat owners normally do anyway, i.e. antifouling.
• Use the most effective, legally approved anti-fouling paints. Apply in sufficient coats to be effective until the next re-anti-fouling ashore.
• Apply extra anti-foulings to niche areas such as rudder trailing edges, keels, especially bilge keels, where turbulent flow accelerates leaching, and where possible to bow thruster casings, stern tube outlets and propellers.
• When scrubbing off underwater hull surfaces avoid doing so in-water.  Wherever possible do so ashore at recognised locations with residue collection facilities and do not allow anti-fouling residues or fouling organisms to be released back into the water.
• Ensure that water intakes/outlets, cockpit and chain locker drainage tubes are not fouled.
• Keep anchors and chain clean. Scrub off as the anchor is lifted. If this is difficult then clean off any mud and weed during the voyage prior to re-deploying the anchor and chain in a new location. Keep the chain locker clean and free of mud and weed.
• If undertaking an international voyage, sailing or taking the boat across bio-geographical boundaries ensure that it has been thoroughly cleaned as above before commencing the voyage.
• Avoid discharging bilge-water in a different location from where it was taken up. However, oily bilge-water must not be discharged into the water at all and the fitting of an oil/water separator will help prevent the discharge of alien species as well.

2. Trailer sailors

Be particularly careful if trailing boats to or from areas where there are known infestations of invasive aliens. Some can survive several weeks even in a dry boat.

• If trailing small boats by road to other places avoid transferring any water, especially bilge water, and ensure the hull and fittings are clean of weed or mud.
• In locations where there is a known risk of contamination the easiest and most effective quarantine procedure is to sponge over with a disinfectant such as paracetic acid (Paraclean) after washing.
• Avoid getting the wheels and axles of trailers muddy or covered in weed. If this happens clean off and disinfect, if necessary, prior to launching at the new location.

Remember, harmful alien invasive species only become known when it is too late. Once established in a new habitat they are impossible to eradicate. Also they may become attached or taken on the boat in a variation of forms from fronds of weed to microscopic eggs and cysts. Just because a harmful alien cannot be seen it does not mean it is not there.

The protection and maintenance of the worlds biological diversity is the duty of all of us. Those who enjoy and use the aquatic environment, therefore, have an especially onerous responsibility as much of their activities are self managed.

Specific Issues for New Zealand

Didymo: Didymo (Styela clava) is an invasive introduced freshwater alga that was found in late 2004 in the Lower Waiau River in Southland. It is easily spread via boats, kayaks and other craft used in rivers and lakes. It is currently not found in the North Island. Click here to learn how to clean your vessel to stop the spread of Didymo.

Sea Squirt (Clubbed Tunicate): The sea squirt Styela clava is now widely spread throughout the Hauraki Gulf and has also been found in Lyttelton Harbour and in Tutukaka marina in Northland. A number of vessels in other locations have also been found to have this species attached to their hulls and this is how the species is spread. Regular cleaning and anti-fouling of hulls is therefore essential in controlling the spread of this organism. To learn more about the sea squirt and how to control its spread click here.

Undaria (Asian Seaweed): The Asian seaweed Undaria pinnatifida was first found in Wellington Harbour in 1987. Subsequently it has spread throughout New Zealand although because it is spread via vessel hulls, it is mainly confined to harbours, ports and aquaculture areas. As with all fouling organisms careful attention to hull cleaning and antifouling is the most important method of controlling the spread.

Didemnum (Whangamata Sea Squirt): Didemum (Didemnum vexillum) has established itself in Whangamata and Tauranga in the North Island and in the Marlborough Sounds in the South Island. It is a yellowish colonising sea squirt that is generally found on structures like pilings, boat hulls and mooring lines. It is a particular threat to the aquaculture industry.  Regular cleaning and anti-fouling of hulls is therefore essential in controlling the spread of this organism. To learn more how to control its spread click here.

Other species of potential risk: There are a variety of other invasive species that have spread from their original habitats to other parts of the world that would be extremely damaging to New Zealand’s marine environment if they were to become established here. Examples of these species include: Chinese mitten crab, Eriocheir sinensis, Mediterranean fanworm, Sabella spallanzanii, Northern Pacific seastar, Asterias amurensis, European shore crab, Carcinus maenas, and the Asian clam, Potamocorbula amurensis. To learn more about these species and how to identify them click on the individual species names above. Any sightings of these species should be reported to NZ Biosecurity Exotic Pest and Disease Hotline Ph 0800 80 99 66.