The whale, estimated to be less than 50 feet long, was seen swimming in the ocean about 250 yards off the coast of Pacifica, Mieke said.
The crab pot had somehow become wrapped around the whale's body but did not restrict it from swimming, Mieke said.
Mieke said the U.S. Coast Guard had issued a small-craft advisory Tuesday, which prevented a Marine Mammal Center rescue crew from taking a boat to the area to try to untangle the creature.
The rescuers instead scanned the waters from a Coast Guard helicopter but did not find the whale, Mieke said.
Mieke said the search will resume today if somebody calls in another sighting.
