On land and at sea, large animals are in 'double jeopardy'

Date: June 9, 2016

Source: Cell Press

Large animals hunted for their parts -- such as elephant ivory and shark fins--are in double jeopardy of extinction due to their large body size and high value, according to a new analysis reported in the Cell Press journal Current Biologyon June 9. The study reveals underappreciated risk to marine species similar to that of iconic terrestrial species, but elevated by key differences in the sea.

"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," says Loren McClenachan of Colby College in Waterville, Maine. "But the extreme values of these species mean that without significant conservation intervention, they will be hunted to extinction."

In the new study, McClenachan, along with Andrew Cooper and Nicholas Dulvy of Simon Fraser University in Canada, identified a taxonomically diverse group of more than 100 large marine and terrestrial species that are targeted for international luxury markets. They estimated the value of these species across three points of sale and explored the relationships among extinction risk, value, and body size. They also quantified the effects of two mitigating factors: poaching fines and geographic range size.

The analysis showed a threshold above which economic value is the key driver of extinction risk. Although lower-value species are influenced primarily by their biology, the most valuable species are at high risk of extinction no matter their size. Once mean product values are greater than US$12,557 per kilogram, body size no longer drives risk, the report shows.

The researchers also uncovered important differences between marine and terrestrial species that point to elevated risk in the sea: although marine products are generally less valuable on a per kilogram basis, individual animals are still just as valuable as the most valuable terrestrial species. An individual whale shark, for example, is about as valuable as the most valuable terrestrial species: rhinoceroses and tigers.

"Hunters don't kill kilograms, they kill individuals, so we need to pay attention to these high values of individual animals," McClenachan says.

The risk to marine species isn't reduced for species with larger ranges as it is on land, either.

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