Art for the Endangered Harbor porpoises

Endangered Harbor porpoises

Fast boats – A threat to harbor porpoises

Harbor porpoises are exposed to a variety of threats. For example, they are affected by the impacts of fishing (bycatch and overfishing), marine pollutants, and underwater noise, among others. The noise causes disturbance via injury and other adverse health effects, and even death.

The current findings on the status of harbor porpoises in German marine areas are alarming. The Red List rates the North Sea population of the harbor porpoise as endangered, and both populations occurring in the German Baltic Sea are considered “threatened with extinction.”

Increasingly, harbor porpoises are being affected by fast recreational boats, which not only cause great noise above the water, but also underwater, and also pose a high risk of collision with the animals.

Article Photo by Ecomare/Salko de Wolf Den Hoorn Texel – Ecomare, CC BY-SA 4.0,

Facts and figures

  • The maximum speed of a harbor porpoise is about 22 km/h
  • Highly motorized boats (up to 1700 hp) race across our seas ten times as fast, jet skis (water motorcycles) are up to five times as fast.
  • There are sound emission standards for boat engines for airborne sound, but underwater sound is not regulated.
  • Until 2008, the city of Travemünde regularly organized power boat races, which were canceled in 2009 due to environmental concerns and were no longer offered. In contrast, there are more offers of high-speed rigid inflatable boat (RIB) tours, jet ski use and banana riding in the North Sea and Baltic Sea.

Underwater noise

Art for the Endangered

ln the oceans, it is becoming increasingly noisy. Numerous human activities, such as the use of fast ferries, passenger and commercial vessels, and the construction of wind turbines, dredging, seismic exploration, the use of sonars, large construction sites (such as the Fehmarnbelt reopening), and blasting contribute underwater noise to the oceans. Today, background noise in the ocean generated by ships is over ten times higher than it was a few decades ago. Shipping and boat traffic are ubiquitous and do not allow marine animals to rest.

Marine mammals such as harbor porpoises, are particularly sensitive to underwater noise, but other species such as fish and crabs are also affected. Medium and high frequencies in particular, such as those typically generated by fast-moving engines of small boats, trigger escape reactions in harbor porpoises and stress them.

Speedboats are a source of noise and danger for harbor porpoises in the sea - Photo: NABU Archiv
Speedboats are a source of noise and danger for harbor porpoises in the sea – Photo: NABU Archiv

Fast-moving boats emit high sound levels underwater from below 1 kHz to well above 150 kHz. This range corresponds to about the top half of a piano keyboard and another 63 (hypothetical) keys beyond that. As a result, they can even interfere with porpoises’ ability to ultrasonically echolocate or communicate (at 130 kHz).

Jet propulsion systems are quieter than outboard engines in this regard, but the potential for interference is highly dependent on how the vessel is driven. When approaching ships and boats, harbor porpoises exhibit strong escape behavior and interrupt foraging and echolocation. Harbor seals and grey seals interrupt their important sleep and rest phases when exposed to ship noise. If such disturbances occur more frequently, this is particularly dangerous for harbor porpoises, since their special physiology makes them dependent on constant feeding.

Little research has been done on noise-induced stress in marine mammals and its relationship to chronic diseases. At breeding time, separation of mother and calf is also possible due to disturbance.

Collision risk

fatal injury to a harbor porpoise caused by a boat propeller
fatal injury to a harbor porpoise caused by a boat propeller

Extremely high speeds of powerboats and RIBs, as well as abrupt course changes that are unpredictable to marine mammals, e.g., when driving jet skis, pose a collision hazard to animals. While it is rare for such collisions to actually be reported, it is likely that the number of unreported cases is high. Porpoise mothers and their calves are particularly at risk, from about May to September in the Baltic Sea and a month earlier in the North Sea.

There is thus a large overlap between this particularly sensitive time for the animals and the water sports and tourist seasons. Harbor porpoise calves swim more slowly, stay longer at the water surface and are also inexperienced in dealing with the many dangers posed by humans. As a result, juvenile mortality is very high.

The relevant regulatory agencies have apparently overlooked the hazards from high-speed travel to date. Environmental impact assessments are therefore not conducted.


  • Dyndo, M., Wisniewska, D. M., Rojano-Donate, L. Et Madsen, P. T. 2015. harbor porpoises react to low Ieveis of high frequency vessel noise. Scientific Reports.
  • Hermannsen, L., Mikkelsen, L., Tougaard, J., Beedholm, K., Johnson, M. Et Madsen, P. T. (2019). Recreational vessels without Automatie ldentification System (AiS) dominate anthropogenic noise contributions to a shallow water soundscape. Scientific Reports 9:15477
  • Hildebrand, J. A. (2009). Anthropogeny and natural sources of ambient noise in the ocean. Mar. Ecol. Prog. Ser 395: 5-20.
  • Wisniewska, D. M., Johnson, M., Teilmann, J., Siebert, U., Galatius, A., Dietz, R. Et Madsen, P. T. (2018). High rates of vessel noise disrupt foraging in wild harbor porpoises (Phocoena phocoena). Proc. R. Soc. B 285: 1872: 20172314 0.1 098/rspb.2017.2314.
  • Wisniewska, D. M., Johnson, M., Teilmann, Rojano-Donate, L., Shearer, J., Sveegaard, S., Miller, L. A. Et Madsen, P.T. (2016). Ultra-High Foraging Rates of Harbor Porpoises MakeThem Vulnerable to Anthropogenic Disturbance.
    Current Biology26, 1441-1446. 0.1 016/j.cub.2016.03.069

This article is a translation of a publication by the BUND Schnelle Boote – eine Gefahr für Schweinswale

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