The secret history of Hope the blue whale has finally been revealed

On the morning of 25 March 1891, a blue whale migrating up the east coast of Ireland was caught by the low tide and stranded on a sandbar just out from the harbour town of Wexford.

The whale was young and not yet fully grown, but that didn't stop the locals from taking great interest in the 25.2-metre leviathan from the deep that had been grounded so close to shore.

After two pitiful days struggling in the shallows, a lifeboat pilot named Ned Wickham rammed an improvised harpoon under the whale's flipper, finally putting the poor animal out of its misery.

The whale was then auctioned off, her body butchered and blubber boiled down. Eventually all that remained was a 4.5-tonne skeleton, which was sold to the Natural History Museum for £250.

After spending decades in the Museum's Mammals gallery, in 2017 the skeleton was remounted in Hintze Hall so that the whale, which has since been named Hope, can greet visitors as they enter the Museum.

For almost 130 years, that has been the sum knowledge of this unfortunate whale's life.

By analysing the chemical make-up of the whale's baleen - the flexible plates that hang inside a whale's mouth - the researchers have found three distinct phases in Hope's relatively short life. While blue whales can live to a hundred years old, Hope may have been as young as 15 when she stranded.   

Dr Clive Trueman, who is based at the University of Southampton and conducted the isotope work looking into Hope's movements, revealed that about seven years before she died, Hope was living in the subtropical waters of the Atlantic - perhaps the Azores, Cape Verde or Mauritania.

After spending at least a year feeding and growing in these waters, Hope began migrating.

Modern blue whales in the northern Atlantic tend to spend their summers feeding around Iceland, Norway and as far north as the Arctic Circle. Ocean upwellings cause plankton to bloom, providing food for the krill that whales feed on. As winter sets in and the ice begins to form, the whales then move south, past the western coasts of Ireland and Iberia, and back into warmer subtropical waters. 

At the moment it is impossible to be certain that this is what Hope did in the year before she died, but the isotopic ratios in her baleen suggest that she did return south.

'The mismatches in isotope ratios are consistent with what we'd expect if she were pregnant,' says Clive.

New data revealing the levels of different hormones present in the baleen confirm that Hope most likely gave birth to a calf in the last year of her life. 

After spending about a year in the subtropical Atlantic waters raising her calf, Hope once more turned north to resume her annual migrations.

It was while moving north along the coast of eastern Ireland that tragedy struck and Hope ended up on that fateful sandbar near Wexford. 

Teeth are made of mineral-rich dentine and enamel, but these baleen plates are instead formed from keratin. This is the same material that makes up our own hair and fingernails. As it's being made in the body, keratin will incorporate certain molecules and so preserve a biological record.

'The nice thing about keratin is that once it's laid down, it doesn't change,' says Natalie.

'Bones and blood will turn over in the body and be replaced, but once keratin has been made it stays like that until it falls off. The same thing applies to baleen.' 

When it comes to certain elements like carbon, the atoms can exist in a number of forms or isotopes. These isotopes differ in mass and are referred to as light and heavy isotopes.

'We can look at the ratio between light and heavy carbon isotopes recorded in the baleen over time, and then we can compare that ratio to what is going on in the oceans and see where they match up,' explains Natalie. 

To do this, the researchers took more than 100 samples from the baleen, working out at around one sample for every four weeks of Hope's final years. These samples were then burnt, and their chemical make-up recorded.

The team then modelled how the isotope ratio varies across the ocean, incorporating the swirling ocean currents, temperature and seasons. 

Clive explains, 'We built some computer-generated whales and put them into our isotope model - something that no one has done before. We made them migrate along different routes, and as they swam and ate they acquired the isotopes found in particular places at a particular time.'

After running hundreds of whale simulations, the team could then see which computer-generated baleen had an isotopic record that best matched that which was actually observed from Hope's baleen. 

New insights into a threatened species

The work is not only shedding light on the Museum's whale but adding to the knowledge about the behaviour and migration routes of modern North Atlantic blue whales.

Very little is known about this population. By the time scientists started to study them, a global whaling industry had already devastated their numbers. While the population has shown some signs of recovery, studying these creatures over long periods of time still has its limitations. 

'We couldn't ever say that what we infer from Hope is true for all blue whales in the north Atlantic,' reiterates Clive.

'But if you find one animal taking a particular route, then it's probably not the only whale doing it.'

Hope for the future

There are many other tissues made by animals that are laid down sequentially, meaning that they also record time - so the same methods used on Hope's baleen could also be applied to other animals. 

Despite having been in the Museum's collections for 127 years, the remains of the young blue whale are still giving up her secrets, paving the way for further work that could help to protect species still alive today.

'We need to keep saving these kinds of tissues, because if we only have the historic collections it becomes more and more difficult to compare what you have in the past to what you've got now,' says Clive.   

'There is a real call to keep refreshing these collections from whale strandings. Museums shouldn't only be repositories of old things.'

• The research has been published in the journal PeerJ, with further analysis of the hormones preserved in the baleen hoped to confirm that Hope did indeed give birth just before her demise. 
• The study is a collaboration between the Natural History Museum, the National Oceanographic Centre at the University of Southampton, and Trinity College Dublin. 
• You can follow both Dr Clive Trueman and Dr Natalie Cooper on Twitter.