​When a ship is not carrying cargo – or not carrying enough cargo - ballast tanks are filled with fresh or salt water. The extra weight provides the ship with stability and maneuverability as it sails. When a ship reaches port, this ballast water is then discharged – in full or partly - refilling again if needed before departure. 

With the immense increase in international shipping over the past half century, the transportation of ballast water from region to region has become a major environmental threat. Discharged ballast water may contain species from different regions and these non-indigenous species can negatively impact the local environment.

In 2004, the International Maritime Organization (IMO) adopted the International Convention for the Control and Management of Ships' Ballast Water and Sediments (BWM Convention). This convention seeks to prevent the spread of “potentially harmful aquatic organisms and pathogens in ships' ballast water" (IMO, 2004). The BWM Convention entered into force in 2017; ships from then on were required to have a ballast water management plan. At that time, members of ICES Working Group on Ballast Water and Other Shipping Vectors (WGBOSV) assessed different sampling methods and tools for ballast water to see how well they could comply with management standards.

Two options were presented - ships exchange their ballast water in open seas, away from coastal areas (D1) or ships treat their ballast water so that in port, only the maximum amount of viable organisms are allowed to be discharged (D2). It is expected that by 8 September 2024, all ships will operate under D2.

​A recent study conducted by members of WGBOSV has now evaluated local and regional risk assessment case studies to provide clarity for situations where ships could be excepted or exempted from ballast water management.

Regulations

Regulations A-3 and A-4 of the BWM Convention enable ships to use exceptions and exemptions (respectively) from ballast water management, if the ship discharges the ballast water at the same location where it originated (Reg. A-3.5), or if a scientifically robust risk assessment has been conducted according to the G7 Guidelines of the BWM Convention for a certain shipping route or hydrodynamically connected area (Reg. A-4). The G7 Guidelines represent three risk assessment types for exemptions, and the risk assessment must indicate an acceptable low risk of introducing harmful aquatic organisms and pathogens (HAOP) through the discharge of unmanaged ballast between the locations of interest.

Okko Outinen, Finnish Environment Institute (SYKE) and member of WGBOSV comments, "In short, if a low risk can be indicated by the risk assessment, exemptions may be granted only between specified locations for a maximum of five years (subject to intermediate review), under the condition that the ship does not mix ballast water from other locations in between". 

"During the 2020 WGBOSV meeting", Outinen continues, "there was a discussion on exceptions and exemptions, and it was agreed that the topic should be addressed to support harmonised implementation of these regulations. Therefore, the group presented regional and local case studies by using existing risk assessment types to demonstrate what is expected from a scientifically robust risk assessment".  ​

Current use

In their study, the group states that exceptions and exemptions should not be considered as common alternatives for ballast water management. "Globally, I'm not sure how often they are used, say Outinen, "I know that several ship operators have been interested in both options and we have also conducted port surveys in Finland for the detection of target species to see whether an exemption could be granted. I am also aware that similar studies have been conducted elsewhere in Europe, as well as in North America. Some exemptions are already in place (for example in Øresund, the narrow strait between Denmark and Sweden) but mainly this is something that ship operators and IMO Member States are still looking for in the future".

At the moment, as there are not many official exceptions and exemptions in place, there is no major impact. However, if the extent of same location for an exception is not limited and exemptions are not based on a scientifically robust risk assessments, there is a risk that new HAOP introductions emerge through the discharge of unmanaged ballast waters.

Outinen concludes, “The understanding gleaned from this study should be used as a guide to help regulators and managers undertake their own risk assessments on exceptions and exemptions for the ports and shipping routes under their responsibility. It is important that exceptions and exemptions from ballast water management do not undermine the initial objectives of the BWM Convention, to mitigate non-indigenous species introductions attributed to the movement of ballast water and sediments by the international shipping industry".