Scientist Ray Sheldon, who was on board the CCS Hudson ship, which set out for the first full tour of America on November 19, 1969 and allowed scientists to explore the ocean, was very impressed by the microscopic plankton that seemed to exist everywhere in the ocean during the voyage. Wondering where and how far these tiny organisms spread, Sheldon and his fellow scientists carried the water they collected from the sea to Hudson’s laboratory in buckets and used a plankton counting machine to obtain data about the creatures they found, such as size and number.
Examining these tiny plankton in the lab, Sheldon discovered that life in the ocean actually goes on with a simple mathematical rule. Accordingly, he concluded that the abundance of an organism is closely linked to its body size, meaning that the smaller the organism, the more it will be found in the ocean. Sheldon thought this rule could govern all life in the ocean, from the smallest bacteria to the largest whales. As a matter of fact, this hunch proved correct, and the Sheldon spectrum was also observed in plankton, fish, and freshwater ecosystems, as is known. But according to the latest research, it seems that this ocean law has been violated.
Large sea creatures may disappear
In a paper published in the journal Science Advances, McGill University’s Eric Galbraith and his colleagues noted that the Sheldon spectrum no longer applies to larger sea creatures. According to the article, due to industrial fishing, the total ocean biomass of larger fish and marine mammals is extremely low considering the Sheldon spectrum is still in effect. “There was a rule that all ocean life followed for reasons we don’t fully understand, and we’ve changed that in the last 100 years,” Galbraith said.
In line with their research, Galbraith and colleagues combined satellite imagery, data on plankton from ocean samples, and marine mammal population estimates from the Nature Conservancy to determine whether the Sheldon spectrum holds up. Comparing current results with estimated data from pre-1850, the researchers found that plankton and small fish were at the same levels, but large fish and cetaceans had declined by more than 2 billion metric tons since 1800. Industrial fishing and unregulated, illegal hunting are thought to be the main reasons for this. If it continues in this way, large sea creatures are in danger of extinction.
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