Aarhus University Seal / Aarhus Universitets segl


Hearing is important for various marine organisms, and many of them use sound for communication, navigation and foraging. This is because sound waves travel farther 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, and one of these criteria 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

A 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 now being implemented. The Danish Environmental Center have recently released this report, revealing a view of impulsive noise sources in Denmark 2016.

Porpoises reacts 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 thousand harbour porpoises get caught every year in the gill nets. As a silent echo of that influence, the human race have had on the world of fish and marine mammals, during the past hundred years. The competition between humans and marine mammals in the hunt for fish, have become more intense as the human ocean activity have grown, and this often results in conflict. Scientists and politicians continues to discus the matter with the fisheries with the hope of agreeing on better and more effective regulations, get more information about bycatch.