Reports of humpback whale sightings off the Scottish coast have increased in recent years, according to the Hebridean Whale and Dolphin Trust. By Terry Howard [CC BY-SA 2.0], via Wikimedia Commons.

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Investigating whale strandings

For over 100 years the Museum has been part of a project to document the cetaceans (whales, dolphins and porpoises) found in British waters and find out what causes them to become stranded on beaches.

Strandings investigator Rebecca Lyal tells us more.

Are many different cetaceans found around the UK?

About 30 species frequent the waters around the UK. The most common are the harbour porpoise and the common bottlenose dolphin. We also have fin whales in the Irish Sea. Some migratory species pop up at different times of the year too.

Back in 2006, a northern bottlenose whale attracted a lot of attention when it got stranded in the River Thames in London. Do cetaceans often swim in the Thames?

It is normal to get cetaceans in the river, but they are usually found in the estuary rather than further upstream. Harbour porpoises are the most common sightings. Hydrophone recordings show that they are buzzing around, but they are restricted to the outer estuary.

You occasionally get lost sperm whales in the outer estuary, but the North Sea is too shallow (only 50-60 metres) to support an animal of that size. They almost always die with an empty stomach. The Thames is not really a suitable environment for cetaceans.

Harbour porpoise, Phocoena phocoena

Harbour porpoises, Phocoena phocoena, are common around the UK coast and even in the outer estuary of the River Thames. By Erik Christensen [CC BY-SA 3.0], via Wikimedia Commons.

What does your job involve?

As a Cetacean Strandings Support Officer, I investigate reports of dead or stranded cetaceans along the English coastline.

Sometimes an animal might have really unusual wounds. Even if that is the case we can usually get a good idea of why or how it died.

What do you do when a stranding is reported?

When a phone call comes in, we try to find out exactly where the stranding is, the stage of decomposition it's in and the size of the animal. Size is important since we could be dealing with anything from a sperm whale (20 metres long) to a porpoise (two metres long). It's crucial to get these details to be able to respond effectively.

Live strandings are reported to the British Divers Marine Life Rescue, who we are in close communication with in case a live stranded cetacean doesn't survive.

We then need to arrange transport to collect the animal or find a freezer to store it in temporarily. If the animal is too large to transport, the post-mortem is conducted on the beach.

Moving a large cetacean is not easy and the body needs to be wrapped up before we can transport it. We need to make sure we have enough people to help.

Harbour porpoise stranded on a beach being measured

A member of HM Coastguard Blyth measuring a harbour porpoise that has stranded in Blyth, Northumberland in August 2015. This species often makes up more than half of all reported UK strandings.

Where do you take the animal?

The specimen usually goes to London Zoo. They have a large autopsy room and specialists who carry out the post-mortem and the associated research from the data collected.

What kind of research can scientists do with a cetacean brought in from a stranding?

At one of the first post-mortems I saw, a student was researching the effect of ultraviolet (UV) radiation on the skin of the animals. Unfortunately we do see cases where animals stranded on a beach in the sun suffer serious skin damage from sunburn.

Sometimes a stranding provides the only tissue from a species that is available for scientific research.

We can also look into what caused the animal's death. This research sometimes reveals the presence of diseases or harmful chemical pollutants such as polychlorinated biphenyls (PCBs). Studying stranded animals also helps us learn about the diet and reproductive patterns of animals in British waters.

Are cetacean strandings common in the UK?

Yes they are. Generally, 400-600 strandings are reported every year. That may seem like a lot but sometimes mass strandings occur where more than one animal strands at once, often alive.

In June 2015, 21 live pilot whales became stranded on the Isle of Skye in Scotland. Although 18 survived and returned to sea, three died, including a female who'd recently given birth. The post-mortem results showed the animals were in a good nutritional state, so we don't know why the pod of whales stranded themselves.

Surely you can't collect all of them?

We tend to just collect the ones in a good condition, as they result in better-quality data. Exceptions are made if it's a less common species. Regardless of condition, we enter all reports of strandings into our database.

The Museum is part of the Cetacean Strandings Investigation Programme, and partner organisations are vital.

The Museum works closely with the Zoological Society of London, Marine Environment Monitoring (Wales) and the Scottish Agricultural College to cover as much ground as possible. England is difficult because it is a large area, and Scotland has islands, which can be tricky to get to.

Curator Richard Sabin looking at the Thames whale skeleton

Curator of Marine Mammals Richard Sabin looks at the Thames whale's skull. After the whale died, its skeleton was donated to the Museum's cetacean collection, available for scientific research.

What causes cetaceans to strand?

It's probably a combination of things. Species react to environmental cues in different ways. Sonar used by the military may be having an effect on some species, although it is difficult to be certain. Some strandings are simply down to the poor health of an individual.

Whales have magnetite (iron oxide) in their brains, which allows them to sense Earth's magnetic field. Some animals have been found stranded at locations where anomalies in the magnetic field hit the coastline.

What have we learned from investigating strandings over the last 100 years?

We now have a long-term set of data showing what species we consistently have around the UK. This data helps influence policies protecting these animals.

The programme has also been a good platform for further research on cetaceans, as we have a long record of baseline data showing us their behaviour and locations. This allows us to do comparative surveys to discover how populations around the UK have changed - or not, in some cases.

Bottlenose dolphin, Tursiops truncatus

Bottlenose dolphins, Tursiops truncatus, can often be seen at hotspots around the UK, such as Cardigan Bay in west Wales and the Moray Firth in Scotland. Courtesy of NASA.

What is it like working in a place with such a remarkable cetacean collection?

I was overwhelmed when I first saw all the enormous skeletons stored in a single room. It was strange seeing all these magnificent animals from all over the world all together in one place, all lined up neatly. It made me wonder about the history and stories behind each specimen.

A complete blue whale skeleton will be suspended from the ceiling of Hintze Hall in 2017. How do you think people will react when they see it?

Historically, the Museum has always changed what has appeared front and centre in the hall. Before Dippy the Diplodocus we had elephants there, and I'm sure displaying them so prominently helped raise awareness of things like the ivory trade and hopefully educated people about the plight of these animals. I hope the whale skeleton will inspire people to consider the future of these giants of the sea.