Your status report on fauna biodiversity (Nature 516, 158–161; 2014) overlooks a group that is causing serious concern among conservationists — sharks, rays and chimaeras. These are particularly vulnerable to fishing and by-catch, in part because they mature late and produce few young.

An estimated 24% of this group, known as chondrichthyan fish, are threatened with extinction under the Red List criteria of the International Union for Conservation of Nature. This exceeds the percentage for birds and is comparable to that for mammals. There are insufficient data to determine status in 47% of chondrichthyan fish, and models predict that many of these could also be under threat, given their similar life history and morphology to the listed chondrichthyans.

Extinction of ocean fish is hard to verify. There is as yet no documented global extinction of a chondrichthyan, but many populations are locally or regionally extinct (such as sawfishes (Pristidae family); see N. K. Dulvy et al. Aquat. Conserv. http://doi.org/zkc; 2014). Some critically endangered species, including the Pondicherry shark (Carcharhinus hemiodon) in the Indo-West Pacific, have not been recorded in decades and may already be extinct.