The voyage approach to managing ballast water is a useful means of categorizing the wide spectrum of suggested control options (see Figure 3-1). Three stages in a ship's voyage and related control options can be identified as follows:
On or before departure. Control is based on preventing or minimizing the intake of organisms during loading of ballast water at the port of origin.
En route. Control is based on the removal of viable organisms prior to discharge of ballast water at the destination port either by treatment or by open ocean ballast water change. Shipboard treatment could commence immediately upon departure and continue throughout the voyage.
On arrival. Control at the port of arrival begins when the vessel's master intends to discharge all or some of the ballast water on board. Control strategies are aimed at preventing the discharge of unwanted organisms that could survive in the target environment.
The viability of various control options is dependent on vessel size and type and the upload and discharge capacity of pumping and piping systems. In the future, modified ship designs that (1) minimize the quantity of ballast water discharged, (2) permit safe ballast change at sea under a wide range of operational conditions, and (3) facilitate cleaning of ballast tanks may be part of an overall ballast water control strategy (see Appendix D).
Although proven shipboard systems for treating ballast water are not yet available (see Chapter 4), there are a number of control options that could be undertaken today that would immediately reduce the transport of nonindigenous species by ballast water. For example, vessels could avoid taking on ballast in ports with high sediment loads, in areas of sewage discharge, or in "hot spots" where certain unwanted organisms were known to be present. A plan for managing ballast water, developed in conjunction with the ship cargo plan, would assist the ship's master in adjusting ballast loading and discharging needs to meet constraints on ballasting in these locations. In addition, a requirement for official logs indicating when and where ballast was taken on or discharged would be helpful for implementing existing (and future) strategies for managing ballast water. The following discussion of options for controlling ballast water includes measures that could be taken in the immediate future, as well as methods that require further development.
Approaches to ballast water control that prevent or minimize the intake of organisms at the port of origin need to take account of ballast requirements for safe ship operation, locations and times of ballasting, and practical limitations on treating ballast water as it is loaded. As the first line of defense to control