NIWA scientists say older hoki are disappearing in the Chatham Rise.
The National Institute of Water and Atmospheric Research recently completed its 20th annual survey of the Chatham Rise, which helps the Ministry of Fisheries set catch limits for commercial species.
Principal fisheries scientist Richard O'Driscoll says good numbers of young hoki were found, but fewer larger, older fish.
He says the mature fish may have been caught, died from some other cause, or simply migrated to other areas.
Dr O'Driscoll says more research is needed, including data from commercial catches of hoki in other areas.
The Chatham Rise is the main nursery area for all juvenile hoki around New Zealand.