African coelacanths are very old. The fossil evidence dates back to its genesis around 400 million years ago, and scientists believed it was extinct until 1938, when the museum’s curator Marjorie Courtenay-Latimer noticed one alive in a fisherman’s net.
Found off the south-eastern coast of Africa, coelacanths live this long – scientists have suspected about 50 years. But to prove that the life was difficult. (Coelacanths are endangered and accustomed to deep water, so scientists can’t just put their babies in a tank and start a timer.) Now a French research team examining their scales with polarized light has determined that ‘they can probably live much, much longer. “We were taken aback,” says Bruno Ernande, marine ecologist who led the study. The new estimated lifespan, he says, “was almost a century”.
His team at the French Institute for the Exploitation of the Sea, or IFREMER, discovered not only that individuals can live to almost 100 years, but also that they have gestation periods of at least five years old, and may not mature sexually until they are at least 40. The results were published Thursday in Current biology. This slow-motion life highlights the importance of conservation efforts for this rare species, which is marked as ‘critically endangered’ on the World Wide Web. IUCN Red List. Only about 1,000 exist in the wild, and their long gestation and late maturity is bad news for their population’s resilience to clashes with humans. “It’s even more threatened than previously thought,” says Ernande.
“This will have huge consequences,” agrees Daniel Pauly, an ichthyologist at the University of British Columbia, who was not involved in the study. Pauly is the creator of FishBase, a database of biological and ecological information on tens of thousands of species. If a fish takes decades to spawn, killing it destroys its potential to rebuild the population. “A fish that needs 50 years to reach maturity, instead of 10 years, is five times more likely to be in trouble,” he says.
Coelacanths have a thickness scales that grow up to two inches long, and for decades ichthyologists have debated how to read these scales for signs of aging. In the 1970s, researchers noticed small calcified structures on them. They thought the rings were age markers, like the rings on trees. However, they did not agree on how to count them: some thought that each notation denoted a year; others believed that seasonal flips created two rings a year. At the time, the best estimate put their life expectancy at around 22 years. This finding, which meant that a 6-foot, 200-pound coelacanth was 17 years old, implied that they would grow very quickly: “They would grow as fast as tuna, which is crazy,” says Pauly.
This is crazy because they are animals with a slow metabolism, which should indicate slow growth. The hemoglobin of coelacanths is adapted to this slow metabolism, which means they cannot take in enough oxygen to support a fast growing fish. Some argue that their tiny gills are further evidence of oxygen limitations. They also lead a very passive lifestyle, resting most of the day in caves and slowly walking through the river. the twilight zone of the ocean, 650 feet and below, when they deign to move. “Overwhelmingly, the biological characteristics indicated a slow-living fish,” says Ernande.
Additionally, scientists who track the lives of individual coelacanths know that 20 years is far too short. In the 1980’s, researchers began sending submersibles and remote-controlled vehicles into a cave housing 300-400 coelacanths. They returned to this place for over 20 years. During each visit, they recognized the individuals by their characteristic white markings. Only about three or four fish from this group would die, and an equal number of new ones would be born each year. This observation provided striking evidence that coelacanths live long lives – even over 100 years, this study supports.