Like humans, some ocean creatures need to breathe air
You wanted to know
A sixth-grade student in Gregg Thompson's social studies class at Woodland Middle School in Gurnee asked, "Why do some aquatic animals need to get air and then go back to the water?"
What comes around goes around. Fish stepped onto land about 230 million years ago and became the first animals.
The whale's ancestor, Pakicetus, a 45-million-year-old crocodile-like mammal, walked off the land and entered the sea, becoming the first link in the Cetacea order that would eventually evolve into one of the world's largest mammals.
"It's amazing that both mammals and fish share the ocean," said David Koontz of SeaWorld San Diego.
"Although they live in the water, marine mammals like whales, dolphins, seals and sea lions, as well as reptiles like sea turtles, need to breathe air.
"So while they spend their life swimming in the ocean, they must still come to the surface of the water from time to time to take a breath of air."
Fish breathe air through their gills. Marine mammals have lungs and take in oxygen through their blow holes or, in the case of manatees and dugongs, through their snouts. Unlike humans, these marine mammals breathe voluntarily.
"Animals need oxygen to survive. Animals like mammals, birds and reptiles get their oxygen by breathing air, while animals like fish absorb the oxygen they need from water taken in through their gills," Koontz said.
Nine minutes is about the very longest time a human can hold their breath under water. Manatees and dugongs can stay underwater about the same amount of time.
Whales, dolphins, porpoises and some seals have a much greater ability to stay submerged and can remain there as long as 90 minutes. Their bodies are specially adapted for these long periods below the surface.
Extra oxygen-enriched blood cells and proteins in muscles help whales, dolphins and porpoises remain under water for long periods where they eat, sleep and play. When diving, their heart rates slow to conserve oxygen and oxygen-rich blood is directed to key organs like the heart and lungs.
Dolphins have flexible rib cages that allow their lungs to collapse, requiring less oxygen to survive long stretches below the surface.
All animals also need water to survive, and although these special mammals live in salt water, they don't drink it. Whales, dolphins and porpoises ingest water through the foods they eat -- plankton, krill and fish.
Turtles evolved some 200 million years ago. Turtles use their mouths to breathe and some have other adaptations to help intake oxygen. Some of the best breath-holders are the sea turtles, with below surface visits of up to two hours.
One turtle's breathing habits might surprise you. The Fitzroy River turtle, unique to Australia, gulps about 40 percent of its oxygen from above-the-surface. Literally on its bottom are air sacs that process about 60 percent of its air intake. Perhaps this bottom-breathing process gives new meaning to the expression, "Bottoms-up!"
Suggested readingSuggested reading
The Grayslake Area Public Library suggests these titles on marine mammals and turtles:
• "If a Dolphin Were a Fish," by Loran Wlodarski
• "Swimming with Sea Turtles," by Miriam Coleman
• "Whale," by Vassili Papastavrou
• "Dolphins," by Dean Stahl
• "Sea Turtles," by Emilie U. Lepthien.