As explained, the 2009 rules require vessels entering California waters to use cleaner fuels and to limit emissions in specified areas. In order to comply and conserve fuel, vessels have slowed down, which has resulted in fewer whales being killed due to collisions with ships, the researchers found.


  • Maritime shipping is dynamic and poses threats to cetaceans and ecosystems.
  • Fuel regulations trigger vessel traffic changes (routing and speed changes).
  • Economic events and regulations at various scales influence vessel behavior.
  • Emission control areas and fuel prices can be important drivers of ecological risk.
  • Results show import of shipping variability in spatially explicit risk assessments.

As seaborne trade continues to grow, threats from shipping to marine ecosystems include oil spills and other water pollution, air pollution, anchor scouring, biological invasions, container loss, chronic noise, and collisions between ships and large whales.

Using AIS data in waters off California from 2008 to 2015, the study evaluated the role of vessel emission regulations and economic events on vessel routes and speeds. Researchers reported vessels navigating around emission control areas (ECAs) or reducing speed when traveling through them.

Large freight vessels decreased speeds from 2008 to 2015 by about 3–6 knots in many areas, with lowered speeds observed in areas of both heavy and sparse vessel use. The timing and location of the speed reductions appear to be most influenced by state and international clean fuel standards, which required the use of more costly fuels.

Therefore, the speed reductions may have provided a more cost-effective means of travel. The study also found temporary speed increases off southern California when vessels used longer routes to avoid traveling through an ECA.

We conclude that the establishment of ECAs had a profound influence on vessel routes and speeds, likely due to the higher costs of clean fuels. Proposals have come before the IMO to establish clean fuel requirements in various locations around the world to reduce air-borne emissions from vessels. Our research suggests such proposals, or other events that may affect marine fuel prices, can have key impacts on vessel behavior. Consequently, it is important to consider this variability when designing strategies to minimize threats from shipping to vulnerable biophysical systems.