By Alice Johnson, Press Office Assistant at the British Science Festival
Unsurprisingly for me, I was a little late for ‘Blue Seas Research: Predators and prey in an ever-changing system’. Five minutes after the talk had begun; I was trying to quietly sneak in to a fully-packed lecture theatre. I was fortunate enough to have been asked last minute to attend Jonathan Houghton’s lecture and write about it. Upon entering the room, I noticed three predators staring back at me from the screen: a leatherback turtle, an ocean sunfish and a basking shark. Each marine animal represented a case study to help us understand the behaviour and threats faced by top predators at sea.
The leatherback turtle is the largest turtle in the world and, believe it or not, they can be found in UK waters. This isn’t so surprising once you find out that it is food that lures them to our shores. However, leatherback turtles have an extremely limited diet… jellyfish! Imagine almost exclusively eating jellyfish? Their soft-bodies don’t damage the leatherback’s fragile jaw and they are easily pierced by the rows of spikes in the turtle’s throat. In addition to being the largest turtle, leatherbacks are also the fastest and can dive the deepest. Jonathan told us that the largest dive he had ever recorded was to a depth of 1,252 metres, around the height of three empire state buildings stacked on top of each other.
So, what threats do leatherback turtles face? Jonathan mentioned the campaign on safer fishing methods and explained that, although considered safer for dolphins and whales, longline fishing is a lot more devastating for a huge variety of other sea creatures, including leatherback turtles. Furthermore, using technology such as satellite transmitters and satellite imagery of sea surface temperatures, it has been determined that 15°C is an important temperature for the turtles. For example, they only venture to UK waters when the temperature is greater than or equal to 15°C. In recent years this is occurring more frequently and the leatherback turtles have been spotted further North, most likely because the waters are gradually warming. Who knows what impacts the rise in sea temperature will have on these archaic animals?
Ocean sunfish are bizarre creatures, which I personally believe resemble decapitated shark heads. Nonetheless, they are quite incredible and can grow to an absurd size. To put the ocean sunfish’s overall growth in perspective, from larvae to adult, Jonathan compared it to like that of a human baby growing to the size of six Titanics! It was originally thought that the only food source for ocean sunfish was jellyfish, but it is now known that they also eat plankton, small fish, molluscs, etc. In light of this discovery, they are considered to be of high importance in the marine food web. Unfortunately, perhaps because of their awkward body shape, ocean sunfish are easily caught in fishing nets as bycatch.
To finish the talk, Jonathan told us a little about basking sharks and the technology used to study them. We were told about CatsCam, which is a multi-functioning tracker device ecologists attach to the sharks. This is achieved by clamping it around the dorsal fin, where it remains until the magnesium link dissolves in the sea water, with the thickness determining the length of time the CatsCam stays attached. The state-of-the-art device is then left to float around the ocean until tracked down by the owners. Not only does the CatsCam film its surroundings, its capability to measure G force enables ecologists to record the basking shark’s movements in 3D. Amazingly, this is the same technology used in smart phones for screen rotation!
I was very glad I had the opportunity to attend this lecture; I feel I have learnt a lot. In fact, Jonathan Houghton has reanimated my desire to become a pirate. Although instead of hunting for chests full of gold, I will instead be searching for lost CatsCams. With a £100 reward for finding one, who can resist?!