The Government is being warned cuts in navy patrols may be jeopardising New Zealand's control over its territorial waters.
Two of the Navy's four inshore patrol vessels have been out of action since last year because of crew shortages, and budget documents show that will continue for at least another year.
The Navy's own figures estimate the ships need to spend about 950 days at sea between them each year to carry out all their tasks.
Budget documents show they'll spend a maximum of just 290 days at sea in the coming financial year.
The documents say decreases in sea days are because of crew shortages, with only enough people in the Navy to keep three ships on the water, and not all at once.
A defence researcher at Victoria University, Lance Beath, says fewer patrols mean a heightened risk of illegal activity, such as illegal fishing, in New Zealand waters.
But a Defence Force spokesperson says the crew shortages have not affected the navy's ability to complete the tasks asked of it by other agencies, including Fisheries, Customs and the New Zealand Police.
A spokesperson for the Ministry for Primary Industries says it is too early to tell whether Defence Force changes have had any impact on the ministry's fishery patrols.