This fin whale stranded on the Isle of Coll in 2004

On investigation this Cuvier's beaked whale, washed ashore in 2006, was found to have a stomach full of plastic debris

This individual was one of many beaked whales washed ashore in March 2008

Strandings

What to do if you come across a stranded cetacean

There are many reasons why cetaceans strand. If you come across a stranded whale, dolphin or porpoise, it is important to check whether it is alive or dead. In many cases this will be obvious, but if it is not, look at the tail, flippers, jaws or eyes to see if they are moving, or whether its body movements indicate it might be breathing. For your own safety and that of the stranded animal, try not to touch it.

Live strandings

If the cetacean is alive:

• If you are in the Argyll and Islands area call HWDT (01688 302620). Otherwise call the British Divers Marine Life Rescue (BDMLR) on 01825 765546 (office hours) or 07787 433412 (out of hours). For any sick/injured seals or abandoned seal pups call Oban Sea Life Sanctuary (01631 720 386).
• Stay clear of the animal, move quietly and ask other people to stay quiet. If there is a large number of people on the beach make sure that the animal does not get crowded and that onlookers are kept at a distance. If anyone on the beach has a dog, kindly ask them to leave the area.
• Check whether there are obvious signs of injury and if possible take a photograph to allow species identification.
• Do not attempt to move the animal or return it to the water without a medical assessment from a vet or someone qualified to deal with strandings.
• Attempting to help a stranded whale or dolphin should be done by trained professionals, but if you wish to learn more please go to the BDMLR website.

Dead strandings

If it becomes clear that the animal is dead, the carcass can still be very useful to scientists, so here is what you should do:

• If the stranding is in the Argyll and Islands area, call HWDT (01688 302620), for anywhere else in Scotland call the Scottish Agricultural College on 01463 243030.
• Take a note of the precise location of the stranding.
• If you have a camera, take several photographs of the body from different angles, and one showing the general location / landmarks.
• Measure it as accurately as you can. This information can help with species identification.
  

Why cetaceans strand and what we can find out

The reasons why whales, dolphins and porpoises strand has long-intrigued scientists. There is no single explanation for why these events occur.

Many animals strand, either alive or dead, because they are ill or injured, and are carried by wind, tide and current into shallow water, and to the shore. Illnesses may be one-off cases, affecting single animals, or epidemics, such as the dolphin morbillivirus which has affected striped dolphins in the Mediterranean since 1990. Where two or more non-dependent individuals, often from the same social group, strand in the same or similar place and time, are usually referred to as mass or multiple strandings. It has been suggested that sometimes when a social group strands, such as pilot whales, it may only be one animal that is ill, but the others follow it ashore and also beach.

Apart from natural illness, there are a number of possible explanations for stranding events. Some mass strandings events have been associated with human activity. One of these is bycatch: the incidental capture of non-target species such as whales and dolphins in fishing nets or creel lines. Cetaceans that have drowned in fishing gear may be blown towards land en masse, and many floating carcasses may come ashore at the same time, such as has been seen with common dolphins in south west England.

Another human activity which may cause strandings is naval sonar. Strandings of beaked whales during the 2000s in the Bahamas and Canaries were linked to the use of naval sonar, which produces a very loud noise, and is thought to affect the diving behaviour of deep-diving cetaceans, causing many animals to strand in a similar place and time.

Sometimes animals from a single or a few groups may strand over a long distance and time. This seemed to occur with sperm whales in the North Sea in the 1990s. Sperm whales are deep-diving animals and if, through some failure in navigation, they enter an area such as the North Sea, which is shallow and full of estuaries and sandbanks, they are not able to successfully orientate or find food and may eventually strand. The original navigational error may be attributed to anomalies in the earth’s magnetic field. If, as has been proposed, cetaceans use biomagnetism to navigate, magnetic anomalies could disorientate them and throw them off course.

What we can learn

As cetaceans spend their entire lives at sea, a stranded animal can provide scientists with a rare opportunity to learn more about cetacean anatomy, physiology, disease and population structure. Firstly, an animal can be examined to find out how it died, by investigating it for signs of disease or trauma. Its foraging habits can also be determined by analysing stomach contents for evidence of what prey it has consumed. Even if the stomach is empty, this is also useful, as it is a sign that, for whatever reason, the animal had not fed for sometime before its death.

Many carcasses are too decomposed for a cause of death to be identified. However, even in these cases, samples and measurements of the stranded animal are useful. Cetacean teeth can be used to give an estimate of the animal’s age. By taking a cross section of the tooth and counting the number of layers, the age of the animal can be worked out in a similar method to that of ageing a tree. In baleen whales instead of using their teeth, growth rings can be counted in the ear bone. Skin samples can be used to find out genetic information about an animal, providing details on population structure and social grouping. Levels of pollutants which accumulate in the fat layer below the skin of cetaceans can also be measured from samples taken from stranded animals. Skin samples may also be used for stable isotope analysis to give an indication of the areas the individual may have travelled to in its lifetime.

Even when a carcass is too decomposed to allow visual species identification, samples of teeth, bone and tissue can still be used to identify species. Therefore, although cetacean strandings are sad events, they provide valuable opportunities to discover more about life history and populations, especially with species that are rarely seen in the wild.