Scientists were working on a plan to help two injured humpback whales return to the Pacific Ocean after a failed attempt to lure them out of a shipping channel using recorded underwater sounds.
Early Friday, the mother and her calf remained at the Port of Sacramento, where they hit a dead-end after traveling 90 miles through the San Francisco Bay and up the Sacramento River.
The use of the humpback whale recordings on Thursday was scientists' first attempt to direct the whales back to sea since they appeared in the Sacramento-San Joaquin Delta last weekend. But, with little success, they called off their efforts shortly before 5 p.m.
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"The biologists were experimenting with different sound patterns and different vessels to see which ones will appeal most to the whales," said Ed Sweeney, a Coast Guard spokesman. "It's going to be a long, slow process."
Scientists said they would announce their new plan for helping the whales Friday morning. It could take weeks to get the whales back where they belong, they said.
If the sound recordings aren't enough, researchers said they might line the channel with boats to herd the whales in the right direction.
On Thursday, researchers began playing the sounds from an 87-foot Coast Guard cutter in the morning, then transferred the gear to a smaller vessel several hours later when the whales did not respond.
Scientists thought noise from the larger ship's generator may have interfered with the whale sounds.
The whales twice began swimming out of the port after the sounds were broadcast from the smaller boat, but both times they turned back into a large basin that oceangoing freighters use for turning around.
The procedure worked in 1985 with a humpback nicknamed Humphrey that wandered for nearly a month in the delta before returning to the ocean.
But biologists said the latest situation is more complicated: It involves a mother and calf rather than a single whale, and the two are much farther into the delta than Humphrey.
The injuries add another dimension, because scientists say they do not know how the wounds might affect the whales' behavior.
"It's not like we're applying something we have a lot of experience with in the past. It's essentially an experiment," said Pieter Folkens, an Alaska Whale Foundation biologist.
One concern is the murky water and numerous estuaries of the delta, a vast network of rivers and canals that drains two-thirds of California's land mass.
Scientists fear they could lose track of the whales if they find their way back to the Sacramento River and are considering marking them with radio or satellite tags that would be attached with suction cups.
If the whales can be returned to their natural habitat, where food is more plentiful and the salt water can heal their cuts, they likely won't need treatment, researchers said.
The injuries were apparently caused by a boat propeller, and scientists checked them Wednesday using photos of the animals swimming in the port.
The mother had a gash 2 feet long and 6 inches deep, filled with blubber. The calf's wound was difficult to assess because it is on the animal's underside, below the water line.
The two likely had been on their northward migration from Mexico up the California coast when they were sidetracked, biologists said.
Because they are at the end of their hibernation season, they have less blubber to rely on for fuel than they would later in the summer or fall.
Shipping and small boat traffic has been halted in the channel, which is 30 feet deep and 200 feet wide. The next ship was not expected to dock until May 23, giving researchers time to escort the whales.