The sticking point in discussions of whale conservation schemes (Nature 481, 139–140; 2012) has been reaching agreement on the total catch that each whale population can sustain. The International Whaling Commission's scientific committee has developed and simulation-tested an adaptive algorithm, the Revised Management Procedure (RMP), to determine safe catch limits. For most populations, RMP limits are below the numbers discussed during the commission's failed 2010 negotiation of catch levels.

The whale-related expenditure of most of the organizations mentioned by Costello and colleagues goes largely to scientific research and outreach, not to protests. These funds have helped to develop tools such as the RMP, genetic techniques to monitor markets and improved methods for estimating whale numbers and demography.

If conservation organizations were to 'buy' whales, it would not necessarily reduce the numbers killed. Most catch quotas set by governments lie well above the numbers actually taken. Even if the more conservative RMP catch limits were applied to a new whale market, 'buying' a given number would not save that number over time. Under an adaptive-feedback management procedure such as the RMP, killing fewer whales one year tends to increase catch limits in subsequent years.