Double the size, double the trouble? Large animals ranging from sharks to elephants face a bigger threat of extinction because of their big body sizes and the value of their parts. This is especially the case for marine species: Individual marine animals are as valuable as the most valuable terrestrial species, according to new findings published in Current Biology this week.
Small species less than 10 kilograms (22 pounds) like parrots, seahorses, and turtles do suffer from trade-driven extinction risk. However, because larger-bodied species tend to have the lowest population growth rates, individuals that are killed are harder to replace. "Hunters don't kill kilograms, they kill individuals, so we need to pay attention to these high values of individual animals," Loren McClenachan of Colby College said in a statement. There are five products that are more valuable than gold: tiger penis, bear gall bladder, rhinoceros horn, deer musk, and Tibetan antelope fur.
McClenachan’s team identified more than 100 megafauna species that are targeted for international luxury markets. They estimated their value across three points of sale – first sale, mean retail, and maximum retail values per kilogram – and then explored how extinction risk, value, and body size relate to each other. The researchers also quantified the effects of poaching fines to identify a threshold above which monetary value becomes the key driver of extinction risk.
They found that body size is the key driver of extinction risk for “lower value” species. But the most valuable species suffer a high extinction risk regardless of size. However, it’s not equal between land and sea. Marine products (like shark fin or manta gills) are generally less valuable than those belonging to terrestrial animals (like elephant ivory) on a per kilogram basis, yet an individual marine animal is as valuable as the most valuable terrestrial species. A whale shark has a maximum potential value of $341,140 in traded parts, which is about the same as that of white rhinoceroses and tigers, which are $368,000 and $350,193 respectively. Nearly half of the species that have maximum potential values that exceed $10,000 are cartilaginous fishes.
And while large ranges buffer the risk for land animals, that’s not the case for those in the ocean. There are tighter controls on land. Furthermore, poaching fines have little effect on extinction risk. They need to be at least 10 times as much to be effective. "We typically assume that if a species is reduced to low numbers, individuals will be hard to find, hunters will stop hunting, and populations will be given a chance to recover," McClenachan added. "But the extreme values of these species mean that without significant conservation intervention, they will be hunted to extinction."
