Aitcheson said most DHBs would have their beds full in the mornings so the reduction to 85 per cent reflected that hospitals were doing acute and urgent work only.
The occupancy rate started higher at some hospitals at the start of the strike than had been anticipated, but it dropped as patients were discharged throughout the day.
The doctors are striking over being rostered on for 12 consecutive days which they say is too long and want it reduced to 10, as well as a drop in night shifts from seven to four.
Aitcheson said the DHBs would continue to follow the plan because it was working well so far.
Labour health spokeswoman Annette King said the DHBs were understaffed due to a lack of funding and said both doctors and patients were being put at risk.
"These doctors are on strike because they are falling asleep at the wheel when they are driving home and they are concerned at their safety and their patient's safety around the hours they are being forced to work."