Noise and porpoises

Please consider the porpoises in the Little Belt

When sailing the Little Belt waters, please be advised that your vessel may be a disturbance to the marine inhabitants. Porpoises, a small whale species, are abundant in the Little Belt, particularly in its narrow parts. And they use sounds as an important part of their life.

Going faster than 5 knots, for example, may cause a disturbance to the whales. Studies show that underwater boat noise is particularly likely to have an impact on the behaviour and foraging patterns of these marine mammals.

Failure to consider the whales may have the following repercussions:
– Interrupted foraging, which may lead to reduced feeding, reducing the fitness and the chances of survival as well as reproduction for the whale
– Fleeing a source of disturbance will increase the whale’s energy consumption, reducing its fitness and chances of survival as well as reproduction
– Long-term stress, leading to a higher risk of disease and a shorter lifespan
– Interruptions of porpoise mothers with calves cause less suckling time, reducing the energy transfer to the calf, possibly leading to increased calf mortality rates.

What you can do

Steady and slow down your boat when there are porpoises in the area. Motor boats going faster than 5 knots are particularly likely to cause a disturbance; this is especially the case in the narrowest part of the Little Belt, with high porpoise concentrations and few escape routes for porpoises.

Recognize and respect the speed limits. There are rules for sailing the Little Belt, including but not limited to, the use of motor-driven vessels (motor boats), jetskis and water scooters, in both of the local police precincts. For instance, please be advised that within a 300 meter distance of the entire coast line, the speed limit is 5 knots. Furthermore, water scooters etc. are not allowed to sail in the areas hatched on the map below.
You are responsible for knowing and complying with any rules and regulations that apply on this matter.

Code of conduct for sailing in waters inhabited by porpoises

As a part of the project ‘Belt in Balance’, Naturpark Lillebælt recently published a memorandum in collaboration with the Institute for Ecoscience at Aarhus University. This memorandum contains a code of conduct regarding whale tourism and boating activity in the vicinity of porpoises in the Little Belt. The recommendations below are founded in said memorandum; find it here (in Danish only).

Adfærdskodeks for hvalturisme og bådaktivitet omkring marsvin i Lillebælt (Code of Conduct) (


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In order to take care of the porpoises in the Little Belt, you should follow these rules:

1. Always try to approach the porpoise parallel – never directly from behind, on an intersecting course, or heading straight for it
2. Never actively move closer than 50 meters to harbor porpoises
3. Always turn off echosounder/sonar when sighting harbor porpoises
4. If the porpoises suddenly find themselves closer than 50 meters from the boat, keep your course and speed constant
5. No pursuit/“hunting” of harbor porpoises by boat, water ski, kayak, surfer, jet ski or fast sailing boat
6. Avoid sudden speed and course changes near porpoises – note that there will be additional noise when reversing
7. Approach the porpoises slowly at no more than 5 knots
8. Limit your observation time to 30 minutes per animal/flock
9. Leave mother porpoises alone with calves – never cut a calf off its mother (e.g. by moving between them or moving through their swimming direction)
10. Be extra vigilant and cautious when harbor porpoises feed (indicated by animals staying in one place for a long time/water slightly rushing or bubbling around animals/many short dives in a confined area)
11. Watch out for signs of disturbances (when you notice them, end your observation time):
– Sudden change in diving behavior
– Longer dives >2 min
– The porpoises stop foraging
12. No feeding
13. No swimming near the porpoises
14. Max 5 knots for all boats within 300m of the porpoise

Watch the movie – this way you can take care of the porpoises (in Danish)

Local tour boats support the Code of Conduct

A number of local tour boats and businesses support and respect the Code of Conduct for sailing responsibly around in the vicinity of porpoises in Naturpark Lillebælt. Please ask the local tour boat operator, or look for this flag on the boat.

Naturpark Lillebælt supports better marine environment every day

This anti-noise campaign, together with the biohuts and the cod stone reefs, are part of the ‘Belt in Balance’ project headed by Naturpark Lillebælt; the project aims to improve the marine environment in the Little Belt.

Relevant links:

Sejlskibet FREM