Ballast water management of international vessels
[Image: Chris Woods, NIWA]
As vessels unload their cargo they pump seawater into ballast tanks to provide stability to the vessel and allow it to operate safety. Many different types of marine plants and animals can be transported in ballast water. These include free swimming species and their juvenile, planktonic life stages, biofouling organisms that grow inside the ballast tanks and organisms from the seafloor that can be sucked into the tanks during loading. If ballast water loaded in a port is discharged at a different location it may release marine organisms, including some pests and diseases.
Since 2000, New Zealand has had an Import Health Standard (IHS) that requires ballast water carried on international vessels to be exchanged in mid-ocean prior to being discharged into New Zealand's territorial waters. Open ocean exchange reduces the density of coastal planktonic organisms present in the ballast water, thereby reducing the risk that they will be discharged in our coastal waters.
The 'International Convention for the Control and Management of Ships' Ballast Water and Sediments has recently been ratified. It entered into force on the 8th September 2017. The convention will require that all international vessels that carry ballast water install an on-board treatment system approved by the International Maritime Organization (IMO). Further guidance on how to meet ballast water requirements can be found on the Ministry for Primary Industries' website.
For more information
- New Zealand Ballast Water Import Health Standard [PDF 161kb]
Additional reading
- Murphy, K., Doblin, M., Boehme, J., Ruiz, G. (2009). Spatial and temporal variation in CDOM and trace elements in eastern Australian ports Implications for verifying ballast water exchange by ships. MPI Technical paper No: 2009/45. 43 p. ISBN 978-0-478-35759-2 [PDF 506 kb]