Aarhus University Seal / Aarhus Universitets segl


Hearing is important to various marine organisms, and many of them use sound for communication, navigation and foraging. This is because sound waves travel further underwater than any other type of energy, even farther than light. Visibility under water is rarely more than 30 meters, but sound can travel for miles. Porpoises, dolphins and other toothed whales also use sonar, in the same way that bats do. They send out short ultrasonic clicks and then use the echo from the surroundings for navigation and hunting, even in total darkness. Other marine mammals, including baleen whales, seals, seacows, some crustaceans, and many species of fish (for example, herring and haddock), use sound to communicate with each other.


  • Ships and offshore-activities, including oil platforms, drilling and windfarms; effects on porpoises
  • Seismic oil exploration; effects on narwhale and baleen whales
  • Underwater blastings; effects on seals and porpoises
  • Sonar, including military anti-submarine sonar; effects on porpoises and seals
  • Pingers (Acoustic alarms to prevent bycatch of porpoises in nets); effects on porpoises


The European Marine Strategy Framework Directive has produced detailed criteria concerning conservation of marine environments, one of which concerns underwater noise. These criteria should be included in the marine environmental condition reports conducted by each member country.

Underwater noise made by humans

Windfarms, shipnoise and fisheries

Ship in the inner danish waters
Photo by Line Hermannsen

One hundred years ago, diesel engines became a regular part of ships. Since then, the contribution of human-made background noise has grown. Now, there is reason to believe that the level of underwater noise is affecting the health of our marine environments. Due to a growing concern surrounding human-made underwater noise, regulations are being implemented. The Danish Environmental Center has recently released this report, revealing a view of impulsive noise sources in Denmark 2016.

Porpoises react to noise


Harbour porpoises reacts to shipnoise
Photo by Jonas Teilmann

New research reveals that...

Due to the fact that harbor porpoises communicate, navigate and forage using sound, porpoises are sensitive to human sea activity. In this international collaboration project, we investigate how noise is affecting porpoises in inner Danish waters, as porpoises in Denmark live in some of the most heavily trafficked regions. Go to the project page and read more about the findings.


Fisheries and porpoises

Research shows that...

More than a thousand harbour porpoises are caught every year in gill nets, a silent echo of the influence the human race has had on the world of fish and marine mammals over the past hundred years. In the hunt for fish, the competition between humans and marine mammals has become more intense as human ocean activity has grown, and this often results in conflict. Scientists and politicians continue to discuss the matter with the fisheries with the hope of agreeing on better and more effective regulations. Get more information about bycatch.