Sitting on the top of a dormant volcano, my phone started to buzz. I was on Ascension Island, in the middle of the southern Atlantic Ocean, conducting fieldwork for one of our shark projects, when I started receiving photos of a large shark stranded on a UK beach.
Confused and a bit bewildered at first, it soon became apparent that this was a bit special. It was 18 March 2023, and the pictures I received were of a suspected female smalltooth sand tiger shark (Odontaspis ferox). I studied the images in disbelief. This was a species that had never been recorded in the UK before. Questions were running through my mind - is this a hoax? Is the location accurate? Why has it turned up by the Isle of Wight?
Investigating shark strandings
What was clear was that it required further investigation. However, I was over 6000 km away and not due to fly home for weeks. I frantically messaged friends and colleagues across the UK to try and get someone down to the site to confirm the identification and secure the body. Sadly, everyone was either busy, tied up with other strandings or overseas themselves. By this time, the news had hit social media, leading to the unfortunate spread of misidentification and scaremongering (although at nearly 3m long, it was probably a larger shark than many people have ever seen – let alone found washed up on their doorstep - smalltooth sand tiger sharks feed on small fish, squid and shrimp, posing no risk to humans).
A member of ZSL’s Cetacean Strandings Investigation Programme (CSIP) team – who recover sharks, turtles and seals in addition to cetaceans – travelled to the site to investigate, but by the time they could get down to retrieve the body, its head and fins had been taken and the carcass opened up.
This was devastating. We had missed our chance to collect valuable samples from the UK’s first record of the species, samples which would help us find out why the animal had ended up here in the first place. Nonetheless, Rob Deaville, CSIP Project Manager, secured what was left of the body and returned it to ZSL HQ for further examination. At the very least, we could obtain a DNA sample to confirm the species identification.
The plot thickens…
Two weeks later, on 31 March, still cursing the missed opportunity, we received an unexpected email from colleagues at Trinity College Dublin. Another suspected female smalltooth sand tiger shark had been found stranded on the rocky shore of Wexford, Ireland.
This time, however, not only was it bigger at over 4m long but, importantly, it was intact. A frantic exchange of excited emails followed, and we began collectively trying to work out the cause of these near simultaneous strandings. Both sharks were female, so we initially wondered whether they had come up onto the relatively shallow waters of the Celtic Sea and Channel to give birth - a behaviour the species is thought to do elsewhere. After the two post-mortem examinations were completed, we started writing up our findings ready for publication.
No sooner had we finished our first draft than Rob received another message. It was 1st of May and a third smalltooth sand tiger shark had been found. This time, it was in Lyme Bay on England’s southwest coast, a mere stone’s throw from my house and, importantly, I was back from my expedition.
I jumped in the car and headed down to meet the fantastic fisher Barry who had found the shark body floating out at sea and, understanding its potential importance, had brought it ashore to report it. He had conveniently been able to keep the shark in his refrigerated van on his driveway (although it certainly didn’t fit in the fish trays that carry his usual catch, Dover sole). I’m not sure his neighbours were as excited as I was though, given the distinctive odour of decaying shark that wafted down the road as I drove up to his house.
When Barry opened the van, it was clear that this was indeed another smalltooth sand tiger shark - although curiously, this time it was a male (easily identifiable by the presence of two claspers by the anal fins) throwing our previous pupping hypothesis into disarray. Confirming the news to Rob, we returned the next day to collect the body and take it to ZSL HQ for post-mortem.
At this point, we had had three animals mysteriously strand between the UK and Ireland within two months of each other. Remember, this was a species that had never been recorded in either country before, nor had it ever been recorded this far north anywhere. Two questions became the focus of our investigation 1) why were these three animals even in the area? and 2) what made them strand nearly simultaneously?
Why were smalltooth sand tiger sharks in UK and Irish waters?
For the first question, we had to investigate the ocean conditions around the time of the stranding. Smalltooth sand tiger sharks generally spend their time associated with the sea floor in warmer, more tropical waters. We therefore examined the sea bottom temperatures in the Celtic Sea and English Channel at the time of the strandings and in the months prior.
What we found was that the water temperatures in summer 2022 were considerably higher than the average for that time of year, and these conditions persisted into winter and through to 2023. We believe that these individuals followed the warming waters up and into UK and Irish waters, expanding their range northwards.
Waters around the UK and Ireland have warmed in recent years due to climate change and we expect these temperatures will continue to warm over the coming decades. As such, we suspect that this will likely not be the last smalltooth sand tiger shark that we see, with our waters becoming (at least temperature wise) more hospitable for the species. Considering 2023 is projected to be even warmer than 2022, we may have a busy few months ahead of us.
These occurrences also serve as a warning that other species may soon follow suit. This highlights not only that we should be proactive in our response to managing new species, but the need to ask governments around the world to rapidly reduce carbon emissions.
What caused the shark strandings?
As for this second question, the answer is far less clear.
We found limited evidence that the animals had been fisheries bycatch. Indeed, only the male shark had any signs of a fishery interaction, with an old small hook found lodged in one of the gill arches.
An alternative hypothesis was that the animals had struggled to find food and starved in this new environment. We found no evidence for recent feeding in any of the three individuals, supporting this idea. Yet, none were in poor physical condition, which is a bit baffling. Further investigations are pending to find potential signs of disease or impairment but, as of now, it remains a mystery. Keep an eye out for developments over the coming months as our investigations continue.
Helping scientists investigate strandings
We are forever grateful to the public for reporting these strandings. They are our eyes and ears and have helped us build a fantastic and unparalleled dataset on the marine species that live around the UK.
If you happen to come across a stranded shark, whale, dolphin, seal, or turtle, please get in touch and let us know (contact details can be found here). In doing so, you will be directly contributing to our understanding of these animals, how they use the UK coast and, importantly, what we need to do to better protect them and marine ecosystems.
Read more about these occurrences in the Journal of Fish Biology.
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