The committee categorized the range of potential strategies for controlling ballast water as follows:

• On or before departure. Control is based on preventing or minimizing the intake of organisms when ballast water is loaded at the port of origin.

• En route. Control is based on the removal of viable organisms by shipboard treatment or ballast change prior to the discharge of ballast water at the destination port.

• On arrival. Control depends on preventing the discharge of unwanted organisms that could potentially survive in the new environment.

The viability of different control options depends not only upon their biological effectiveness but also on vessel size and type and the loading and discharge capacities of ballast pumping and piping systems. Given this diversity of vessels and the complexity of ballasting patterns, the committee determined that flexibility in managing ballast water is essential for adequate protection against introductions of unwanted nonindigenous aquatic organisms.

Biological scientists cannot currently state what level of ballast water control is effective, and existing guidelines for controlling introductions of nonindigenous aquatic nuisance species do not identify an acceptable level of risk. Risk-based approaches to managing ballast water, using quantitative risk assessment methodology, are being investigated in the United States and Australia.

There is currently no universally applicable option for controlling ballast water that can totally prevent the unintentional introduction of nonindigenous aquatic nuisance species. The use of available control methods is limited by requirements for safety, environmental acceptability, technical feasibility, practicability, and cost effectiveness. Nonetheless, there are a number of control options that could be undertaken today that would immediately reduce the transport of nonindigenous species by ballast water. These options include avoiding ballasting if water is likely to contain unwanted organisms (for example, in areas of sewage discharge or high sediment loads). A plan for managing ballast water developed in conjunction with the ship cargo plan would provide flexibility for meeting contingencies and avoiding ballasting in certain locations.

Both shipboard and shore-based facilities for treating ballast water merit further investigation. The concept of shore-based reception facilities for oily ballast has gained acceptance, although such facilities are not widely used. Shore-based treatment of ballast water may have some advantages, but there is no precedent in the United States for recovering associated infrastructure costs, and shipboard treatment is more likely to be implemented.

In the absence of a universally applicable method of managing ballast water, the committee identified a need for additional research and development to improve methods of killing or removing organisms in ballast water. In the view of the committee, international coordination of research on ballast water would both stimulate activity and avoid duplication of effort.