In the first six months of 2017, 90 assaults occurred on mental health staff, compared with 84 in the whole of 2016.
In June, the nurses' union raised concern about assaults and staffing levels in Wakari Hospital's ward 9B.
Nurses' union organiser Celeste Crawford said the board was recruiting nurses from the United Kingdom and the US to fill longstanding vacancies.
She had no issue with the board looking overseas if that was necessary, but was disappointed at the lack of an immediate response.
''As a long-term response ... we're happy, but we're disappointed that there's no short-term options there that our members can turn to if numbers on the ward increase.''
Lower patient numbers recently had provided some relief, but numbers would increase again in due course, she said.
She said the board was also considering increasing security staffing at Wakari Hospital.
In his written response to the OIA, chief executive Chris Fleming said the board maintained close oversight of assaults.
''Any assault is unacceptable and is taken very seriously. A number of strategies are in place to support moving to a state where assaults are minimised and do not occur.
''These strategies include close monitoring of staff skill mixes and resources at any one time in inpatient areas, careful risk assessment and management plans for patients, sensory modulation techniques, ongoing education and training ...''
The nurses union also complained about an increase in patient-on-patient assaults. The board said those figures could not be released as it would take too long to collate information.