Hawaii’s bigeye tuna fishery is on course to hit its annual catch limit for waters west of the islands on Nov. 19, meaning the supply of locally caught ahi will likely drop sharply more than a month before demand peaks during the year-end holidays.

Western Pacific Regional Fishery Management Council senior scientist Paul Dalzell told the council’s scientific committee about the estimate Thursday.

Isle fishermen, like their counterparts elsewhere, are required by international treaties to limit their take of bigeye tuna in the western and central Pacific to make sure the fish’s population doesn’t collapse.

This year, Hawaii-based longline fishermen must stop catching bigeye tuna west of Hawaii once the fleet has caught 3,763 metric tons. As of Wednesday, they had brought in 3,057 metric tons.

The fishery will still be able to catch bigeye in waters east of the islands even after the western area catch limit is reached. But the ahi in the east tends to be less plentiful, particularly during the last few months of the year.

Handline fishermen may continue to fish in waters west of Hawaii, but the volume of fish brought in by this fishery is limited.

Consumers are expected to still be able to buy ahi at local markets, however, as dealers are likely to import and sell bigeye from fishermen outside the islands.

Even so, many island residents prefer to eat ahi caught by the Hawaii-based fleet because locally caught bigeye isn’t treated with carbon monoxide to preserve its color like some of the fish delivered by air freight.

Hawaii demand for tuna peaks at the end of the year as families eat ahi to celebrate Thanksgiving, Christmas and New Year’s.

The problem is expected to be a recurring one for the fleet.

To address the situation, the council’s Scientific and Statistical Committee on Thursday discussed a proposal to change the period by which the annual catch is measured to a 12-month span other than the calendar year.

Starting the catch year in September and ending it in August, for example, would ensure that the fishery would continue to be able to deliver ahi through December every year. But there’s a chance fishermen may make less money under such alternatives.

The committee decided to recommend keeping the status quo, in part, because Hawaii-based fishermen haven’t requested a change and because dealers would still be able to supply the Hawaii market with ahi from elsewhere.

The Western Pacific Regional Fishery Management Council is due to consider the catch year issue, including the committee’s recommendation, at a meeting next week.

Any change to the catch year would not affect the catch limit for 2010. It would only take effect in subsequent years.