| Good afternoon everyone. |
| Well, with some of you about to go out on field work |
| it's timely that in this afternoon's session I'll be sharing some ideas about the reasons why groups of whales and dolphins |
| sometimes swim ashore from the sea right onto the beach and... |
| most often, die in what are known as 'mass strandings'. |
| Unfortunately, this type of event is a frequent occurrence in some of the locations that you'll be travelling to, |
| where sometimes the tide goes out suddenly, confusing the animals. |
| However, there are many other theories about the causes of mass strandings. |
| The first is that the behaviour is linked to parasites. |
| It's often found that stranded animals were infested with large numbers of parasites. |
| For instance, a type of worm is commonly found in the ears of dead whales. |
| Since marine animals rely heavily on their hearing to navigate, |
| this type of infestation has the potential to be very harmful. |
| Another theory is related to toxins, or poisons. |
| These have also been found to contribute to the death of many marine animals. |
| Many toxins, as I'm sure you're aware, originate from plants, or animals. |
| The whale ingests these toxins in its normal feeding behaviour |
| but whether these poisons directly or indirectly lead to stranding and death |
| seems to depend upon the toxin involved. |
| In 1988, for example, |
| 14 humpback whales examined after stranding along the beaches of Cape Cod |
| were found to have been poisoned after eating tuna that contained saxitoxin, |
| the same toxin that can be fatal in humans. |
| Alternatively, it has also been suggested that some animals strand accidentally by following their prey ashore in the confusion of the chase. |
| In 1995, David Thurston monitored pilot whales that beached after following squid ashore. |
| However, this idea does not seem to hold true for the majority of mass strandings |
| because examination of the animals' stomach contents reveal that most had not been feeding as they stranded. |
| There are also some new theories which link strandings to humans. |
| A growing concern is that loud noises in the ocean cause strandings. |
| Noises such as those caused by military exercises are of particular concern |
| and have been pinpointed as the cause of some strandings of late. |
| One of these, a mass stranding of whales in 2000 in the Bahamas |
| coincided closely with experiments using a new submarine detection system. |
| There were several factors that made this stranding stand out as different from previous strandings. |
| This led researchers to look for a new cause. |
| For one, all the stranded animals were healthy. |
| In addition, the animals were spread out along 38 kilometres of coast, |
| whereas it's more common for the animals to be found in a group when mass strandings occur. |
| A final theory is related to group behaviour, |
| and suggests that sea mammals cannot distinguish between sick and healthy leaders |
| and will follow sick leaders, even to an inevitable death. |
| This is a particularly interesting theory |
| since the whales that are thought to be most social - the toothed whales - |
| are the group that strand the most frequently. |
| The theory is also supported by evidence from a dolphin stranding in 1994. |
| Examination of the dead animals revealed that apart from the leader, |
| all the others had been healthy at the time of their death. |
| Without one consistent theory however, |
| it is very hard for us to do anything about this phenomenon |
| except to assist animals where and when we can. |
| Stranding networks have been established around the world |
| to aid in rescuing animals and collecting samples from those that could not be helped. |
| I recommend John Connor's Marine Mammals Ashore as an excellent starting point |
| if you're interested in finding out more about these networks, or establishing one yourself. |