Summary
In their Policy Forum review “Do the largest protected areas conserve whales or whalers?” (Science, 28 Jan 2006, p.525), Gerber and co-authors criticised the scientific basis of the International Whaling Commissions’ (IWC) Southern Ocean Sanctuary and determined that commercial whaling based on the IWC’s management procedure for setting catch limits (the Revised Management Procedure, RMP) would provide superior conservation performance to sanctuaries. Their conclusions were based substantially on a simple life history model which explored the efficacy of spatial closures for maximising whale population growth rates under reserve and non-reserve conditions. The model mimicked the function of a sanctuary by reducing mortality for a proportion of the population (20%), such that whales were ascribed demographic features according to their temporal occupancy patterns of a patch (reserve or non-reserve). This was compared to an ‘RMP-like’ scenario where a generic 10% reduction in mortality is applied to reserve and non-reserve areas. In the southern hemisphere, baleen whales are compulsory migrators with almost the whole population moving between high latitude feeding grounds and low latitude breeding grounds annually. We contend that such predictable and demographically complete dispersal is not appropriately defined in the Gerber model. Here we show that when whale dispersal between a reserve and non reserve is modelled as (1) a random exchange of all life stages (including calves) and (2) net rate of dispersal is modelled as equal mixing (50%), then a reserve (sanctuary) will perform just as well, if not better than a RMP-like scenario. We conclude that there yet remains a well developed theory of MPA for the high seas, let alone for highly migratory species such as baleen whales, and that use of simple population modelling approaches based on life history theory to assess the efficacy of MPA’s needs further development.