Primary production required to sustain global fisheries D. Pauly* \& V. Christensen I.How did they calculate total Primary Production Required (PPR) to sustain the reported catch rates? 2.Why were levels of open ocean PPR cause for concern regarding sustainability of harvest (even though it was only 1.8% of estimated total PP)? 3.What reasons may account for the higher PP of shelf systems than open ocean gyres? .