Increasingly, whales and dolphins around the world are facing modern pressures upon their environment – pollution, accidental capture in fishing nets, and disturbance from vessels, particularly high-speed craft.
Recreational activities in inshore waters have burgeoned recently, and can pose a major threat to whales and dolphins either by direct injury when animals are accidentally cut by the boat’s propeller, or by interference or stress caused from the high frequency sounds made by the vessel’s motor.
There is no reason why boats and dolphins should not be able to co-exist if care is taken to observe the following rules:
- If you sight dolphins at a distance, make forward progress maintaining a steady speed, slowing down to six knots or less when you are within a kilometre of them.
- Do not chase dolphins, drive a boat directly towards them or encircle them; wherever possible, let them approach you. If they choose to bow-ride, maintain a steady speed and course.
- Do not respond to them by changing course or speed in a sudden or erratic manner; slowing down or stopping suddenly can confuse and alarm dolphins as much as sudden acceleration.
- Allow groups of dolphins to remain together. Avoid deliberately driving through, or between, groups of cetaceans.
- Avoid close approach to dolphins with young. You risk disrupting mother-calf bonds and expose inexperienced young to stress and possible boat strikes.
- Do not swim with, touch or feed dolphins, for your safety and theirs. Beside the stress you can cause them, remember that just as in humans, diseases can be spread by close contact, and dolphins are larger than humans and can cause unwitting injury.
- Ensure that no more than two vessels are within a kilometre of dolphins at any one time and no more than one boat is within close proximity. Refrain from calling other vessels to join you.
- Always allow dolphins an escape route. Avoid boxing them in between vessels.
- Move away slowly if you notice signs of disturbance, such as repeated avoidance behaviour, erratic changes in speed and direction, or lengthy periods underwater.
- Possible sources of noise disturbance can be avoided by ensuring speeds are never greater than ten knots, and by keeping the engine and propeller well maintained. On the other hand, care should be taken to avoid collision with dolphins when using sailing boats and boats with low engine noise, as the animals are less likely to hear the vessel until it is close.
- People regularly using vessels in areas where dolphins are known to occur should consider fitting propeller guards to minimise the risk of injury to dolphins.
Remember that dolphins and porpoises use sound as a daily part of their life, for locating and capturing food, locating and communicating with one another, detecting predators, and forming a picture of their underwater environment in often very dim light. Many of the sounds made by craft overlap with the frequencies used by dolphins and porpoises; particularly those caused by cavitations of the propeller blade, producing a very loud broadband, high frequency noise. This causes interference with their daily activities, sometimes excluding them from preferred feeding or nursery areas. It can also lead to undue stress, particularly when mothers are pregnant or with small young. Scientific studies have shown that dolphins respond negatively to craft moving directly at them, increasing the time they spend underwater and often swimming rapidly away from the source.