Historic whale and dolphin stranding data made public for the first time

Ellen Coombs is studying whale evolution for her PhD at the Museum, and has been delving into the strandings data to see what can be learnt from these historic records as part of a new scientific paper published in Marine Mammal Science.

'It is one of the longest systematic cetacean stranding data sets in the world,' says Ellen.

Between 1913 and 1989, all records of stranded whales and dolphins on UK shores were sent to the Museum. Since 1990, the dedicated UK Cetacean Stranding Investigation Programme (CSIP), funded by the Department for Environment, Food and Rural Affairs, took over the recording of these data, although strandings can still be reported to the Museum. Around the same time, the Irish Whale and Dolphin Group was set up in Ireland to record cetacean strandings there.

In the 106 years represented by the full data set, there have been more than 20,000 reported strandings from 28 different species of cetacean. There are about 90 cetacean species in the world - so roughly a third of them have been spotted in UK waters.

The majority of these strandings represent the most common species found in UK waters: the harbour porpoise, short-beaked common dolphin and long-finned pilot whale.

Yet the benefit of strandings records, as opposed to counting living whales and dolphins, is the opportunity to document rarer, shyer and more transient species that may be found around the country.

Hidden among the records are some more unusual sightings, including some of the deepest-diving mammals in the world. Cuvier's beaked whale has been known to descend 2,992 metres for up to 137 minutes at a time. It's rarely sighted on the surface, but the species does keep cropping up in the stranding records.

Similarly, while there was a lot of excitement surrounding the appearance of Benny the beluga in the Thames estuary this winter, there are actually two other records of beluga washing ashore in the UK in 1932 and 2014, while in 1949 two narwhals stranded.

Recording whale extinctions

Researchers are able to use strandings data to track whale population numbers. Paradoxically, if more dead whales wash up on beaches, it is often a sign of a thriving population. If no cetaceans are spotted (even dead ones), it may indicate their numbers are struggling.

One of the most poignant moments recorded in the data set is the loss of blue whales from around the British Isles. The largest animals ever to have lived, they once migrated through UK waters - until they were the target of intense hunting at the start of the twentieth century, which decimated their numbers. 

The last blue whale to strand in the UK washed up in 1957, nine years before nations agreed on a global ban on hunting the cetaceans.

But the blue whales were not alone in being targeted. Whalers concentrated on most of the large whale species, particularly baleen whales. These include more familiar species such as humpback and minke, but also sei and fin whales.

'There was a drop in baleen whale standings after the Second World War,' says Ellen. 'We speculate that this was because of a huge increase in post-war whaling and fishing to feed and fuel the starving population of Europe.

'We know that fishing and whaling increased in the 1950s, and we found that there were even a few years in this decade where we had no baleen whale standings at all. This downward trend continued into the 1960s as numbers of baleen whales remained low.'

In recent years the numbers of cetacean strandings being recorded have been on the rise. This might not sound like a good thing, but could be down to a number of positive factors.

The first is simply that there are more people aware of the UK's marine life and recording what they find on the beaches. The ubiquitous use of smartphones means that not only are people more likely to positively identify what they find, they are also more likely to report it to the correct organisations. 

It could also represent an increase in the overall numbers of cetaceans now living around the British Isles, although it is important to note that this is not easy to prove. There has been a corresponding increase in the number of whale and dolphin sightings in general, however. 

Diving deeper

With this research, Ellen has only scratched the surface of what can be done with the data.

'The level of detail in the 20,000 records is mind-blowing, especially since 1990, when it started being recorded by CSIP,' explains Ellen. 'There is so much information in the data. The scope is just huge. In many of the modern records you get incredibly fine scale details for some specimens, such as testicle size.

'This means that the possibilities of what you could do with the data are incredible.'

The data could be used to focus on a smaller time period or narrowed down to just a single species. This could then be compared to timings of military sonar exercises, for example, or levels of by-catch over the same period, potentially showing any relationships that may or may not exist between human activity and cetacean strandings.   

The records also underscore the importance of the stranding network and the vital need to keep it funded. Not only does the data give insight into the presence and distribution of cetaceans, it can also help answer questions ranging from the parasitology of these animals to their relationship with their environment.

'It is very important for conservation around the UK, as you want to know where cetaceans are stranding and why,' explains Ellen.

'If all of a sudden a species disappears, it says a lot about the health of the oceans.'