Underwater noise from fairways – policies, incentives and measures to reduce the environmental impact
Underwater noise and its negative impact on marine life is a growing environmental concern where scientific knowledge is increasing but mitigation is scarce. This report is the outcome of a joint effort of the IVL Swedish Environmental Research Institute and the Swedish Maritime Administration that addresses this challenge.
Motivated by environmental concerns and coming EU legislation, our vision is that Sweden should become the first country to implement national incentives for underwater noise mitigation. The technical aspects of ship underwater noise are relatively well known.
At cruise speed, cavitation at the propeller is typically the dominant source of underwater noise, but this is not true for all ships. Standardised measurement methods exist but are costly to implement. Prediction models are useful for noise mapping and fleet-wide estimates but not sufficiently accurate for individual ships.
The environmental impact of underwater noise from shipping has gained increased scientific attention in recent years. While many studies have been made, dose-response relationships and thresholds for different effects are largely unknown. Behavioural effects, including escape reactions, difficulty to avoid predators and masking of important communication calls, have been observed across a large number of species upon exposure to ship noise.
There are no national or international binding rules on ship underwater noise emissions. The International Maritime Organisation is currently updating its voluntary guidelines on ship underwater noise. The EU is introducing legislation on permissible levels of ship underwater noise in the environment, which is expected to come into force in member states within a few years.
Technical methods for mitigation of underwater noise are known but not independently validated. Ship speed reductions may reduce underwater noise but may incur increased operational costs at the ship owners. Stakeholders in ship underwater noise mitigation are found across ship owners, the ship design and technology industry, research bodies and authorities.
Through interviews and workshops a network of relevant stakeholders in Sweden has been established. A stakeholder analysis showed that there is a need for more knowledge on ship underwater noise and its environmental impacts as well as its mitigation. Fairway design for reduced transmission of underwater noise to the environment was investigated by long-term measurements at different sections of the fairway leading to Västerås in lake Mälaren. Neither depth nor a turn could be demonstrated to have an effect on the radiated noise.
A more detailed experiment would be required to clarify if fairway design is a viable alternative for noise mitigation. Six different ways of designing a financial incentive for ship underwater noise reduction were described. Rewarding speed reductions or technical measures for noise mitigation is feasible but the scientific basis is not clear. An incentive may be based on a silent ship notation from a classification society, but these are not commonly issued.
A noise inquiry may be performed, but it may be difficult to identify the most relevant mitigations without underwater noise measurement. Bespoke measurement stations at or near port inlets may be a cost-effective way to collect measurement data, but the accuracy of such opportunistic measurements would need to be improved if the data is to be used for a financial incentive.