Sam and her brother, Tom thought how lucky they had been to be invited on an Octonauts mission.
But today they were patrolling over mud and sand with marine biologist, Shellington. "Most people think sediment is boring," he said, "but that's only because they've not really explored it." Tom and Sam thought most people were probably right, as the flat sea bed passed beneath the GUP-D. "Wow," said Shellington, indicating the sensor display, "Look at that. The sensors show it's over 6 metres long. Let's go and see."
As they came closer they could see an enormous fish, but like nothing Tom and Sam had seen before. It had a strange shaped head, covered with bony plates and a pointed snout. In the GUP-D's lights they could see it was olive-black above and white below. It didn't have scales, but it had five rows of light-coloured bony platelets running along its length. "You see those plates along the side," said Shellington, "they're called scutes. This is a sturgeon; they're very rare, and critically endangered. This is probably a female, as they are bigger than the males. They've been known to grow to 6 metres and this one is longer than that. She might be over a hundred years old. Shall we go outside and take a closer look?"
They quickly put on their diving suits, checked the equipment and left the GUP-D. Taking care not to disturb the seabed and stir up clouds of mud, they swam over to the enormous fish. Close up Shellington showed them that underneath, between the mouth and snout were barbels that the sturgeon was using to feel around in the mud, before a tube-like mouth sucked up whatever she had found.
Shellington greeted the sturgeon. "Hello," he said. "How are you?"
"Hungry," she replied, "I'm always hungry these days," and carried on eating.
"Not the talkative type," Shellington whispered to Sam and Tom.
"You are very big," Tom said to the sturgeon. "I bet you're very old. I mean, you must have had a really interesting life, done lots of things, and know lots."
If sturgeons could smile, she would have done at Tom's attempted flattery.
"Oh, I am," she said. "I'm probably the oldest and biggest of my kind. I've not seen any bigger for a very long time. But then I've seen so very, very few of us at all."
"Can you tell us how old you are?" Sam asked.
"I don't really do big numbers," the sturgeon replied. "Not much call for counting as a fish."
"Perhaps you could tell us about your life," suggested Shellington. "Then we could work it out from what you've seen."
"Would you really like to know? It is an awful lot. So many things have happened and changed since I hatched."
"Yes, please, we really would," urged Sam.
"Perhaps you could start at the beginning," Shellington suggested. "Do you know where you hatched?"
"Well, of course, I do," she replied. "I have found my way back many times since then. The smell of my own river draws me back. Not that I can tell you in terms that would mean much to you. It's about five days swimming, in that direction." She indicated with her snout. "But I can travel quite fast when I want to, I don't spend all my time grubbing around on the seabed. This tail can still drive me along in mid water. I can outrun most things that might try to eat me, although there are not many of them around nowadays, and I can catch small fish, too."
Shellington checked his instruments. "She must mean the West coast of France," he said. "Probably the Gironde, which flows into the sea through the Garonne estuary there. It's the only place they're known to have bred in recent years."
"I came out of my egg into fresh water, a long, long way from the sea. It's quite different you know. It tastes different, you feel heavier in it, and your body just feels, well, different," she said. "The water was quite deep, not as deep as this, nor as cold, and the bottom was gravel swept by fast moving water. I stayed in the fresh water for a while. You can tell the passage of time from the time the big light is on, and the angle it makes, and I should think it did maybe three complete ups and downs while I was moving down to the sea."
"Was that three days?" asked Tom.
"No, silly," said Sam, "she means three years. Up is when the sun is highest in the sky in midsummer, and down when it's at its lowest in midwinter and days are shortest."
"You're right, Sam," said Shellington, "that's what we know about sturgeons. But I can see why Tom might have thought she meant days."
"For a few more turns I went into the sea when the big light was down, and came back to where the water is mixed when it was up."
"What did you eat in the fresh water?" Tom asked.
"Pretty much what I eat now, only smaller. There are small crunchy things that turn into things that break through the surface and fly away. If they're not eaten first of course. There is squidgy stuff that comes in hard cases. Sometimes the case comes in two pieces."
"That'll be insect larvae and molluscs," explained Shellington.
She went on. "And other crunchy, wriggly things like these here. Excuse me."
The sturgeon's barbels had been probing the mud all the time she had been talking, and suddenly she pushed her mouth into the seabed and they just had time to see her suck up a prawn and a small fish.
"Oh, very nice," she said. "My favourite. Two for one, if you get me. The little fish live in the same burrow as the crunchy things. Nice combination of textures and flavours."
"That must have been a Dublin Bay Prawn, or Scampi, and a shrimp goby of some sort," Shellington said.
"We like fried scampi," said Sam.
"They're caught by trawlers in places like this," Shellington went on. "And that could be dangerous for our friend here. Although you're not allowed to catch sturgeon, they can be caught by accident. In America they are tracking sturgeon and then warning fishermen not to fish where the sturgeon are. It's called bycatch when you catch something you weren't after, and it's the main danger to these fish in the sea. We'll keep a lookout for trawlers."
"You're right," interrupted the sturgeon. "I've had to swim very fast to get away from these big mouth things that follow the boats on the surface. In fact there's one not far away. It's time to go." And she headed off.
"Back to the GUP-D full speed," ordered Shellington. "We'll follow and make sure she's OK."
The GUP-D's sensors had no trouble following the huge fish, but it also showed up the net. And instead of heading away from it, she was heading into it. "Can't we help?" shouted Sam.
"I think so," said Shellington. "We'll use the grabbers."
By now the sturgeon had realised her mistake and had turned round, but she had left it perilously late, and it looked like she wouldn't make it out of the track of the edge of the net, even going as fast as she could. Shellington headed towards the wire which kept the mouth of the net open. Just as it looked like he was going to run into it, he put the GUP-D into reverse and kept it just ahead of the net. Then he reached out with the grabber, latched onto the wire, and made GUP-D go stern first towards the surface. Just in time the corner of the net lifted clear of the seabed and the sturgeon swam underneath it. Shellington released the grabber and stabilised the GUP-D before it went upwards out of control.
"Wow, that was close," he sighed. "Let's go and see how she is."
Back in the diving suits they saw that she was busy sucking up food again.
"Hello," she said. "You managed to dodge the big mouth thing, too. Well done. Speed, that's the thing. That's how I do it."
"I don't think she realises we rescued her," said Sam. "No matter," Shellington replied. "She's alive, that's the main thing."
"So," he went on. "Tell us what it was like in the sea when you were younger, please."
"Well, it was so quiet for a start. The boats on the surface were much smaller, there were less of them, and only a few of them had those whizzy things instead of a tail, which make all the noise. But they were the biggest, and they used to throw lots of nasty, smelly rocks over the side. You can still find them now."
Shellington explained to Tom and Sam, "I think she's talking about steam ships. Before oil became the main fuel they used coal, and when it had been burnt, they would throw the clinkers over the side. And you can still trace the old steamer routes from the clinkers on the seabed. Propellors came in at the end of the 1900s. The other boats would have been sailing boats"
The sturgeon went on. "None of them could swim beneath the surface, then, like you do. If they came below the waves, they'd just go straight down to the bottom. All the people died. People trying to swim like fishes is quite recent, and they still don't do it very well. Then there was a new breed of boat-fish. They did swim beneath the surface, were made of something much harder and heavier than the older boats and had whizzy things instead of a tail. They couldn't dive for long at first, but they got bigger, and faster, and stayed down longer, and funnily enough they became quieter. But they did some very strange things. It must have been just before I made my first trip back to the fresh water where I was hatched. There was a lot of activity on the surface, lots of noise, and lots of the boats sinking. And some of these boat-fish would spit a smaller boat-fish at one of the floating boats, there'd be lots of noise and the floating boat would sink. Sometimes the floating boats would put things in the water which would make an enormous amount of noise, and sometimes the boat-fish would sink. But the good thing about that time was that the boats towing the big mouth things went away."
"I think she's talking about the first world war," said Shellington. "That was the first time that submarines were used to any great extent. So given that females make their first spawning migration aged about 14 to 18, she must have hatched before 1900. That's a bit older than we have records for. We think they might live to 100. But she is bigger than we have records for, too."
"Please tell us about going back up the river where you hatched," urged Sam.
"River. Is that what you call the fresh water? You can feel the eggs forming inside, and you just know you have to stop eating and go back. Do you get that feeling?" she replied.
"No, we don't," they said together.
"How strange." She sounded puzzled. "So back I went. It would be about the time the big light was about a half of a half of the way up the sky."
Tom and Sam looked at Shellington. "That would be in March or April, which fits with what we know about their migration pattern. Please carry on"
"The water got fresher and fresher, and shallower, and lighter, and you could see more. When the big light is off, some of the time there is a smaller light, and in those days, when the smaller light was off too and you were in still, shallow water you could see lots and lots of tiny little bright lights. You don't see them now, there are lights on the shore and they're too bright. There were lots of us then, going a long way up the river, females like me and males too. And we'd lay our black sticky eggs in the gravel. Then we'd all head off back to sea."
"I did that many times, every three or four cycles of the big light, laying more eggs as I got older. But the river got more and more difficult to get up. It was straightened, and barriers put across. And the water got nastier and nastier. It was worst at the point where we went from the sea into the river. In the end, we just couldn't get through it. I sometimes wonder what happened to the young ones left up the river. Are they still there, or did they try swimming through the nasty water and died? I've not been able to get back for longer than I can remember."
"That's so sad," said Sam, her eyes filling with tears. "So you just spend your life at sea now, do you?"
"Yes, except when I'm driven to go back to the river, but can't go up it. So many things have changed. You remember I told you about the boat-fish? Well, it happened again. I was still going up the river to lay eggs then, so it was quite a long time ago. But it went on longer, and the big boats had mostly stopped throwing the nasty, smelly rocks over the side, but when they sank there was this really nasty, thick, black stuff that came out and floated up to the top."
"That must have been the second world war, and ships used oil as fuel and carried it as cargo," explained Shellington. "Please, if you don't mind telling us, what other things have changed?"
"Ah," she said, "there's a new stuff in the sea. It started a bit after the second lot of big boat sinkings and boat-fish. It doesn't go away. Take these big mouth things the boats tow along the sea bed. In the old days, they'd get wrapped up round a rock or a sunken boat, and get left behind. After a few egg layings up the river, they'd be pretty much gone. But the new ones seem to last forever. And there are lots and lots of bits of the same stuff around – big bits and small bits – it seems to get everywhere."
"What do you think she means? Shellington," Sam asked.
"Plastic, I think," he replied. "It's one of the biggest problems in the ocean, now. It doesn't rot. It gets broken down into smaller pieces, and horrible chemicals attach to it, then small sea creatures eat it, and bigger sea creatures eat the smaller ones, and build up the chemicals in their bodies. And some, like turtles or sea birds eat plastic by mistake, and starve to death. Maybe that's why she's always hungry."
"And," she went on. "Fishes. There are less of them, less different sorts, and what are left are smaller. I'm glad I don't have to eat just fish, but then the really big fish that do have gone too. Some of them are air-breathers, like you, and there aren't many of them around either, these days. Mind you, I'm glad those big ones, with the big mouths full of teeth, that made a lot of noise from a big lumpy head – you might have seen one – have gone. They could make a meal of me."
"Does she mean whales?" asked Tom, who knew they had to come to the surface to breathe.
"I should think so," Shellington replied. "And probably, sperm whales, which use sonar to hunt and would be quite capable of dealing with a 6 metre fish."
"Is it just me," she asked, "but I get the impression that the hard bits on the things I eat are getting thinner? Not that I'm complaining, they're easier to eat, but it can't be doing them any good."
"No, you're right," said Shellington. He explained to Sam and Tom. "As the CO2 in the atmosphere increases, more of it gets dissolved in the sea, which makes it more acid, and creatures that make shells find it more difficult to do that. It's not good for them. We've got a hard job undoing the harm we've done to the sea"
"Some things do seem to have got a bit better lately. I'd love to be able to get back up the river again. Do you think that might happen?" she asked.
"People are working on it," Shellington said, "and we're going to make sure they do as much as they can. But we've got to go now. As you said, we breathe air, and we don't have too much left. Come on, Sam and Tom, back to the GUP-D. Thank you for telling us your story, maybe we'll meet you again."
"Thank you," echoed Sam and Tom.
"And thank you for listening," she said, "and for lifting the edge of the big mouth thing. I might not have made that without your help."
Tom thought she winked at him.
"Wasn't she nice?" he said. "She must have been even older than granny."
"Much older," said Shellington when they were back in the GUP-D. "Let's see what Captain Barnacles thinks."
Back at the Octotopod they told the rest of the crew of their meeting with the sturgeon, and asked Captain Barnacles what could be done for her.
"Well," he said, "It's going to be really difficult. We'll have to get a lot of people to change their ways if her river is going to run clean again, and some expensive work will be need to change the way the river flows to create the shingle banks she needs to lay her eggs, and to build by-passes so she can get past the barriers. But it can all be done. We've just got to persuade all these people that it's worth it. Octonauts, let's do this!"