Oil exploration plans in eastern Russia are a serious threat to gray whales in the area, say scientists with the International Whaling Commission (IWC

The Rosneft company is due to begin a seismic survey around Sakhalin island within the next few weeks.

The IWC's Scientific Committee is "extremely concerned" about the plans and is calling for a postponement.

The gray whale population is critically endangered, with only about 130 animals left and only 20 breeding females.

Russia says it is aware of the problem, but the company's capacity to shift is limited for financial reasons.

Western Pacific gray whales (also known as grey whales) come to Sakhalin each summer to feed, and seismic survey work - which involves producing high-intensity sound pulses and studying reflections from rock strata under the sea floor - can seriously disrupt their feeding.

The small area where the whales congregate has shallow water, and scientists suspect this is where mothers teach their calves how to feed at the sea floor.

The IWC's head of science, Greg Donovan, said the survey work was planned for the period "when there's probably the highest density of gray whales and particularly mother-calf pairs.

"The Scientific Committee is requesting them to postpone the survey until next year, and to do it as early in the season as possible when there are as few whales there as possible," he told BBC News.

"We actually made a similar recommendation to another company, Sakhalin Energy; they have followed that recommendation and this year, they are carrying out the survey with a very detailed mitigation plan as early in the season as possible."

The mitigation plan includes a provision that testing must stop if mother-and-calf pairs appear in the area.