Kelly Swing gives inaccurate numbers for marine fish species on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. He also mistakenly conflates the scientific process of species assessment for the Red List with the separate political process of IUCN member voting (Nature 494, 314; 2013).

About one-quarter, or 4,337, of some 17,000 species of marine fish are on the IUCN Red List (not fewer than 100 species out of 25,000, as Swing writes). Of those, 416 species have been placed in a threatened category (Critically Endangered, Endangered or Vulnerable) and 1,180 species were classed as Data Deficient.

The IUCN Tuna and Billfish Specialist Group has assessed all 10 species of billfish and 51 species of tuna and mackerel through a series of regional workshops, unhindered by the “IUCN's worldwide voting procedures”. Seven species meet the IUCN threshold for a threatened category (B. B. Collette et al. Science 333, 291–292; 2011). The sale of billfish has since been banned in the continental United States.

The IUCN Marine Biodiversity Unit's Global Marine Species Assessment programme is now evaluating all remaining marine fish, and aims to finish within 5 years (