A governor in Russia's Far East says the trawler that sank in the Sea of Okhotsk, killing at least 56 of the people onboard, was carrying only about a fifth of the ballast it should have been, making it severely unstable.

Thirteen people remain missing from the Thursday sinking; 63 others were rescued.

Initial reports suggested the trawler had collided with an ice floe or other large object.

But later reports cited survivors as saying the boat sank when it was pulling in a full net that weighed as much as 80 tons.

Oleg Kozhemyako, acting governor of the Sakhalin region, said Saturday that the trawler normally would have 250 tons of fuel, but was carrying only 57 tons and had not taken on adequate water ballast to compensate.