On three occasions this year, smalltooth sand tiger sharks (Odontaspis ferox) have either washed up or been spotted in Irish and British waters. Sightings of the tiger shark are unusual given they would normally be found in more southern waters. In April 2023, one was found dead on the rocks at Kilmore Quay in county Wexford. Dr Jenny Bortoluzzi, research fellow at Trinity College Dublin has been examining this phenomenon and joined RTÉ Radio 1's Today with Claire Byrne to discuss the findings. (This piece includes excerpts from the conversation which have been edited for length and clarity - you can hear the discussion in full above).
What is a smalltooth sand tiger shark?
"A smalltooth sand tiger shark is a type of shark that would spend a lot of its time towards the bottom of the sea. It lives mostly in deep waters and they're found in the Mediterranean Sea, but also in Colombia and in various places in the world where they would live below 200 meters. Occasionally they will come up in groups towards the surface," says Bortoluzzi. Physically "they kind of look a bit ragged," she explains. "Their counterparts and themselves are sometimes called ragged tooth sharks, so they've got quite long teeth that are used to cling on to things like octopus or small fish prey and crustaceans. Small pray that they would find on the bottom of the sea."
Is it unusual to see one in Irish seas?
"We would have recorded them only as far north as the Bay of Biscay, possibly one in Normandy that was unconfirmed. But in this situation they are more than 200 miles further north than where we would normally find them. So it was very unusual to get these three specimens in a short time frame, together, in the British Isles and Ireland."
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Are we seeing them in Ireland because of climate change?
Yes, climate change and marine heatwaves. "When we had a look at environmental data to try and understand why they were here and why they appeared, what we noticed was that the waters around the UK and Ireland have been warmer than normal. We've experienced marine heat waves which means that the water at the sea bed is much warmer than it would normally be," she explains. "We think that that has meant that they are able to travel further north than they usually are found."
Saturday April 1, 2023: A 14ft smalltooth sand tiger shark washes up in Wexford
"We had heard that there had been one on the south coast of England and when we got this e-mail and phone call from the Swiss tourist, we thought at first it would be a Basking shark which are really common around Irish coasts. Then he sent us photos and told us he believed it was a smalltooth sand tiger shark and we looked at the photos and he was absolutely correct," Bortoluzzi recalls. "When we saw the teeth, first of all, that confirmed it wasn't a Basking shark, who don't have visible teeth. But we knew immediately that it was something very special and unusual, so we rushed down to Kilmore Quay to try and get there in time before the tide came up and took it away."
The Swiss tourist who found the shark thought it was about two metres long, "so we thought we'd be able to pick it up and take it back to to the lab," she says. "But actually when we got there it was an almost four-and-a-half metre long female shark. So what we had to do was try and take as much information and samples as we could in-situ, before the tide stopped us from doing so."
Why did it end up here? What happened to it?
"They're also quite a rare species, so we don't know much information about them and their biology. So one part was to try and find out what had happened to them and the other part was to get information about their biology, their reproduction and the things they feed on, for example."
Because they normally live so deep down in the water, scientists don't get a chance to examine them closely. "We wouldn't encounter much and when they die they obviously end up in the middle of the ocean or get eaten by other things. So it's not very often that we get washed up specimens anywhere, it happens on occasion and when it does happen we can get a wealth of information from those specimens."
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"Once we understood that it was possibly environmental factors that brought it here, we wondered if even though it was able to travel here, it was unable to survive here because it wasn't its natural habitat. What we saw was that there was no starvation signs, so we believe that all three specimens were in good body condition, hadn't even starved, and there were no obvious signs of being caught by fishing gear on at least two of them. The third one had a hook in its mouth but nothing drastic that would signify that they had been caught and died in fishing nets," Bortoluzzi says. "So we actually haven't answered the question. We sort of eliminated some possibilities, but we're still looking into toxicology and pathology to try and get some of those answers. But it's a lengthy process."
What should you do if you come across a washed up smalltooth sand tiger shark?
Bortoluzzi encourages anyone who comes across something to contact someone. "Whether it's scientists or organisations which you can just give a quick Google and find contact details for, the information makes its way round to whoever needs it and someone will be available to come and have a look," she says.
If it's a live stranding there are networks to contact. The Irish whale and Dolphin Group would be a good place to start.
