BUBBLE NETS AND FOOD CHAINS
YESTERDAY TOM AND JULIE were telling their cousins about the whale watch we went on back in June—how exciting it was to watch the whales as they fed on fish and took care of their babies. Haley and George wanted a chance to see whales up close too, so today their parents drove all four kids to Provincetown for a trip on one of the boats in the Dolphin fleet.
While they’re gone, I’ve spent part of the afternoon down on the beach at low tide, digging for clams and quahogs on the exposed flats.
Digging for Clams
This is what a clam hole looks like.
Soft-shell clams live about six inches deep in the sand or mud.
Clams eat plankton that they filter out of the water during high tides.
Now I hear their car tires crunch on the driveway by the house, and the doors slam. Excited voices come closer, and in a minute I see Julie, Haley, Tom, and George racing along the beach toward me.
George and Tom screech to a halt, spraying sand, and peer into my metal clam basket. “Not bad,” says George, holding up one of the larger clams. “Are we going to have them for supper?”
“That’s the plan.” I toss him a clam I’ve just pulled out of a hole in the sand. “Did you see any whales?”
“Lots and lots!” Tom responds. “Even more than when you took us in June, Gramps! And guess what? We saw Salt! Remember?”
“Salt?” I ask, brushing sand off my hands and arms. “You better remind me who Salt is.”
Tom rolls his eyes. “You remember! We saw Chrystal and her calf, Etch-a-Sketch, on our other trip. And Jane, the whale expert, told us Chrystal was the daughter of a really famous whale named Salt. So this time we got to see Salt, who is Etch-a-Sketch’s grandmother.”
Just then Julie and Haley arrive—they’d stopped to inspect a jellyfish on the beach. “Did you tell him about Salt?” Julie asks breathlessly. Tom nods, and she goes on with the report.
“We saw Salt and lots of other whales,” she says. “And just like last time the water was filled with little fish all around the boat. And bigger fish like stripers and bluefish were swimming around and eating the little fish. It was awesome!”
George is looking quite serious. “Gramps,” he says, “I’ve got to tell you the most amazing thing.”
“What’s that?” I wonder what he thinks is so important.
“The whales work together to get their food! They actually work as a team!
Whales work together as a team to trap the fish they eat.
Haley picks up the story. “That’s right. We even saw them blowing bubbles to surround the fish they wanted to eat.”
“Really?” My knees are tired, so I sit back on the sand and they all plop down around me. “How do they do that?”
Haley looks at her brother.
“After we saw the bubbles, the whales came up through them with their mouths open, scooping up food. So I went over and asked the scientist about it,” George explains. “She said some of the whales work together to create a bubble net, and then other whales herd fish into the net from below.”
“Some whales work together to create a bubble net, and others herd the fish into the net.”
“Right,” says Tom, nodding vigorously. “We could see a circle of bubbles, and then suddenly two or three whales would come shooting up through the middle with their mouths wide open, just sucking in little fish and those little shrimpy things called krill.”
“Now I remember,” I say, massaging my sore knees. “We saw the bubbles on our earlier trip, too, and the whales coming up through them, didn’t we, Julie?”
“Yes,” she confirms. “But this time it happened six or seven times, right beside the boat.”
“George, I’d like to know more about those bubble nets,” I stand and brush the sand off my legs. “Could you do a little research on your dad’s laptop and see what you can find out for me?”
“Sure!” says George. He and Tom head off—they want to try fishing for crabs using mussel guts as bait. Julie and Haley stay to help me dig more clams.
IN THE EVENING we’re invited down to the summer house for dinner with Haley and George’s family. First we eat the clams, steamed and dipped in melted butter. The main meal is swordfish, with mashed potatoes and fresh corn on the cob. Yum! Fourteen of us are seated around the table, and there’s lots of talk about the whale watch trip.
After dessert has come and gone (vanilla ice cream with chocolate sauce), George brings his father’s laptop to the table. Before dinner he had googled bubble net feeding and found some YouTube videos showing whales feeding this way.
Whales Team Up in Amazing Bubble-Net Hunt
“The video I like the best shows humpback whales feeding in Alaska,” George says, bringing up a video on the screen. “These are the same kind of whales we saw today. Check this out!”
George runs the two-minute video four times, stopping the action now and then to let the others see the circles of bubbles, and then the great mouths of the whales as they surge up through the trapped fish.
Julie is most impressed by how the whales worked together to capture the fish, and by their calls. “Some of them make that singing noise—to scare the fish, I guess,” she says, “and others blow bubbles. Then some whales herd the fish into the bubble net. Finally they all swim to the top inside the bubbles, with their mouths wide open.”
Haley is listening carefully. “It’s kind of like my soccer team,” she suggests. “We have defenders and midfielders and attackers. The whales have singers, herders, and bubble blowers. Then they all attack together!”
I like Haley’s comparison. “That’s what we call cooperation,” I tell her. “By working together the whales catch more fish than if each whale chased them alone. Do you know what kind of fish they were eating?”
Haley starts to tell me when George jumps in with the answer. “Those are herring—it said so on the video, and that’s what the scientist on the boat said, too.”
“Right.” I smile at Haley. “So if the whales eat herring, what do herring eat?”
The children fall silent, looking around at each other. Finally Tom speaks up. “I think they eat krill,” he says. “At least, the scientist talked about krill a lot.”
“Okay, so what are krill?” I ask. Tom leaps to the computer and starts a search: What is krill? The National Geographic website he chooses shows a picture of a little shrimp. Tom reads the first paragraph aloud:
The lowly krill averages only about two inches (five centimeters) in length, but it represents a giant-sized link in the global food chain. These small, shrimp-like crustaceans are essentially the fuel that runs the engine of the Earth’s marine ecosystems.
“What’s a crustacean?” Julie wonders aloud.
“You know—like the shrimp we eat with cocktail sauce, the ones we peel first,” Tom answers. “See the picture? It looks kind of like a baby lobster.”
Krill are very important food for whales and many kinds of fish. They feed on phytoplankton.
George looks closely at the screen. “The fuel that runs the engine of the Earth’s marine ecosystem,” he reads. “What exactly does that mean?”
“It means that many, many sea animals live on krill, or they eat other sea animals that live on krill,” I say.
“And not just whales. Julie says you saw striped bass and bluefish feeding along with the whales. In the video George found, we could see lots of gulls and terns diving down and grabbing herring. Do any of you know what a food chain is?”
“I do,” Tom says quickly. He grabs a pencil and a piece of paper. Starting at the top of the paper, he draws a vertical chain with five big links in it. It looks like this:
“Now let’s put the whale at the top, in the first link,” he says. In that link he writes whale.
“The whale eats the herring, so that comes next.” He writes herring in the second link. “Then the herring eats the krill, so that’s the third link,” he mutters, writing krill.
Looking up from the paper, he asks, “What do the krill eat?”
George consults the computer. “It says here that krill feed on phytoplankton. Phytoplankton are microscopic, single-celled plants that drift near the ocean’s surface and live off carbon dioxide and the sun’s rays.” He looks up. “Hey, krill actually eat plants, like deer and cows do!”
I know something about this, so I join in. “The word phytoplankton means ‘drifting plant.’ These plants are so tiny you can hardly see them, and they float along the surface of the ocean. George is right—the krill graze on them like deer or cows graze on grass.”
Phytoplankton are sea plants eaten by lots of sea animals, like whales and shrimp.
“Okay, sea plants.” Tom writes it into the fourth link. “So we’ve got whales eating the herring that eat the krill that eat sea plants. So where do the sea plants come from?”
“It says that the sea plants live off carbon dioxide and the sun’s rays.” I grin mischievously. “Does that sound familiar, Tom?”
Tom’s eyes grow big, and he begins hopping lightly from one foot to the other. “Oh … wow!” he whispers. Then more loudly, “It’s photosynthesis!”
This kind of phytoplankton looks like a little bug. It looks big here but is very tiny.
Here you see another kind of phytoplankton, connected like a chain of diamonds.
These phytoplankton form a different kind of chain.
Various kinds of phytoplankton all living together.
This phytoplankton looks like a baby octopus.
Julie turns to George and Haley. “Tom’s the Gas Guy,” she reminds them. “He knows all about photosynthesis.”
Tom is taking a walk around the table, talking to himself out loud. “I thought photosynthesis only happened on land!” he says excitedly. “So it happens with plants in the water, too. And water covers three-quarters of the Earth. That must be gazillions of plants!”
Julie is waiting impatiently. “Come on, Gas Guy, tell Haley and George about photosynthesis!”
Tom hesitates. “I know about photosynthesis on land, but I don’t know how it works with plants in the water.”
Phytoplankton take in carbon dioxide and give off oxygen, like plants do on land.
“How about telling us about photosynthesis on land, and maybe we can translate that to drifting water plants,” I suggest.
“Okay.” Tom launches into his explanation. “Photosynthesis is about how sunlight shining on the leaves of plants turns carbon dioxide gas into carbon and oxygen. Carbon dioxide is part of the air all around us. The carbon from the carbon dioxide stays in the plant to help it grow. The oxygen is set loose by photosynthesis and goes back out into the air, where we breathe it. We can’t live without oxygen, so the plants are doing a really important job for us.”
He stops briefly. “Here, let me show you a picture.” He searches for photosynthesis and clicks on an image.
George and Haley look closely. They can see that the gas containing carbon and oxygen is labeled carbon dioxide. And they see water from the ground coming into the plant through its roots. The water also has oxygen in it, Tom explains. The water and CO2 mix together in the leaves of the plant and get heated up by the sun. Energy from the sun takes the oxygen out of the water and sends it back into the air for us to breathe.
“So, Gramps,” Tom goes on. “There are these plants—the phytoplankton—drifting around in the ocean. Remember when Julie told us how the ocean sucks up a lot of carbon dioxide, like a sponge? That must be how those sea plants get their carbon dioxide. And there’s lots of water because they’re floating in it. So the sun shining on the water heats up these plants, and that triggers the photosynthesis!”
“That sounds about right to me,” I answer with a nod. “And the most amazing thing is that those phytoplankton produce about half of all the oxygen in the air we breathe. So they’re really important to us. In fact, we probably couldn’t live without them.”
“Got it.” Tom stops pacing around the table and picks up his pencil again. In the bottom link of the chain he writes carbon dioxide, and beside it he draws a big sun.
“There!” he says. At the top of the page he writes Food Chain of the Humpback Whale.
He’s about to fold the paper and put it away when I say, “Tom, I think there’s one more link in the chain.”
He lays the sheet back on the table. “But nothing comes before photosynthesis …,” he starts to say.
“No—the missing link is at the top of the food chain, not the bottom.” I point to the link that says whale.
All four children look at me blankly. I give them a hint. “Remember the story of Moby-Dick?”
George reacts first. “Hunting the great whale …” he murmurs.
Tom’s eyes light up again. He quickly adds another link at the top of the chain. In it he writes people. Then he looks at me. “But people don’t hunt whales anymore,” he announces hopefully. “That was a long time ago.”
They all wait quietly to hear how I respond.
“You’re partly right, Tom,” I say seriously. “In this country we protect whales by outlawing whale hunting. But in some countries, like Japan and Norway, whale hunting is still allowed.”
Next to the link at the top of his whale food chain he adds, but only Japanese and Norwegians!!!
With lots of extra exclamation points.