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Coral reefs provide vital habitats for schools of reef fish species across the globe, but many are at risk from coral bleaching due to climate change and increasing ocean acidification. In order to assess the health and best conservation practices for struggling reef fish, we need to know more about their life cycles including trends in growth rate and maximum age. A recent study published in the journal Coral Reefs looked at three species of tropical snapper in Western Australia to try and ascertain their maximum age and found one individual that was 81 years old. This staggering age puts the Midnight snapper, Macolor macularis, at two decades above the previous estimate for maximum life expectancy and the oldest tropical reef fish in the world.
The researchers sampled great snappers from four locations, from the Chagos Archipelago in the central Indian Ocean to the Western Australian coast. They analyzed the annual growth bands of sagittal otoliths (ear bones) to estimate the age of the fish as you would with tree rings and found two of the three species they were sampling to be the longest-lived tropical reef-associated fishes recorded to date. Eleven of the total sampled were over 60, with one single Red bass, Lutjanus bohar, clocking in 79 years and our record-breaking Midnight snapper at 81. The octogenarian was discovered in the Rowley Shoals, which sits 300 kilometers (186 miles) west of Broome, Western Australia.
The incredible ages of these geriatric fish push the maximum ages for tropical reef fish to 20 years older than previously thought possible. As well as being a remarkable finding, the data is vitally important for managing the conservation of these fish. Animals with advanced maximum ages indicate that they have a low rate of natural mortality in order to reach such seniority. A greater age also means they are more likely to exhibit a slower reproduction rate and as such are more at risk from harvesting practices that could remove viable adults from the population.
“Until now, the oldest fish that we’ve found in shallow, tropical waters have been around 60 years old,” said Australian Institute of Marine Science (AIMS) Fish Biologist Dr Brett Taylor, who led the study. “We've identified two different species here that are becoming octogenarians, and probably older."
The next steps are to identify how these species are reacting to varying water temperatures to ascertain if they’ll be able to cope when temperatures warm in their entire range. The results from this research showed that for Red bass, maximum life expectancy nearer the equator was 50 years compared to 80 years at higher latitudes where the temperatures are cooling, painting an uncertain future for their longevity in a warming ocean. For now, the researchers are still reeling from the fact that some of these fish have been kicking around since 1939.
“It survived the Great Depression and World War II,” said Taylor. “It saw the Beatles take over the world, and it was collected in a fisheries survey after Nirvana came and went. It’s just incredible for a fish to live on a coral reef for 80 years.”
