Restricting the chinook salmon sport fishery on the Yukon River to zero retention later this week is under consideration by the federal Department of Fisheries and Oceans.

Fisheries biologist Pat Milligan said this morning with the below-average return of chinook so far, additional measures may be required to limit the number of salmon caught.

The commercial fishery, based primarily in the Dawson City area, has been closed so far this season.

'We are not expecting a strong return above the border based on the indications we have seen so far,' Milligan said.

'We are at the point now where we think it may be prudent to limit the sport fishery retention to zero.'

Anglers, Milligan explained, would be permitted to catch chinook salmon but would have to release them.

The aboriginal food fishery remains open.

The biologist said the low return, combined with the composition of six-, five- and four-year-old fish which make up the annual migration, begs the question whether the Yukon River chinook population is entering another downward trend.

The population had been showing positive signs over the last few years since it bottomed out in 2000, Milligan said.

He said the number of returning six-year-olds has been proportionately higher this year while the number of five- and four-year-olds has been noticeably lower.

But the spawning years for all three age classes were strong, so there was no reason to expect the imbalance, Milligan pointed out.

He added there is some indication that a larger area of the Bering Sea was cooler than normal.

While the lower temperatures may have had more of an impact on the younger fish, what exactly is behind the below-average return and the age class imbalance is still something that needs to be looked at, he said.

'We were a little bit surprised about how there were no more four- and five-year-old fish,' he said. 'It may signal a change in the marine conditions but we will have to wait and see.'

Management officials were initially looking for a return of 45,000 fish to the Yukon-Alaska border on the Yukon River, which would have provided for the required spawning numbers and allowed for a full aboriginal, commercial, sport and domestic fishery.

The run forecast has declined significantly since it began.

It's now expected the total run will be somewhere between 21,000 and 31,000 salmon.

Official tallies to date show that 124,622 chinook have passed by the Pilot Station Sonar on the Alaska side near the mouth of the Yukon.

That's down 30,000 from the 10-year average, and 44,000 from the same time last year.