SACRAMENTO — With two wandering humpback whales refusing Wednesday to budge past a bustling steel bridge across the Sacramento River, rescuers escalated their tactics to prod the wounded leviathans back to the sea.
Rescuers played the sounds of humpbacks feeding in hopes of luring the whales, both bearing injuries probably inflicted by a ship's propeller, toward saltier water where their wounds could heal better.
When that effort proved fruitless in coaxing the humpbacks beneath the bridge, the flotilla late in the day began playing the sounds of killer whales feeding on California gray whales. They also tried a variety of man-made shrieks from a synthesizer.
The risk, authorities acknowledged, is that hostile sounds might put the whales under even more stress, causing their deteriorating health to worsen.
But frustrated rescuers from the Coast Guard, National Marine Fisheries Service, and California Department of Fish and Game seemed resigned to pull out all stops as hope began to dwindle.
"We've been trying to do this in a very measured, gradual approach," said Trevor Spradlin, a National Marine Fisheries Service wildlife biologist. "But we don't seem to be making as much progress as we'd hoped."
Spradlin said it remained unclear how much longer the whales could survive out of their natural saltwater environment. Their normally slick skin has grown pitted and their wounds are failing to heal properly in the fresh water of the Sacramento River and delta.
"It's not just the wounds. It's the skin in general. Fresh water isn't good," said Joe Cordaro, another National Marine Fisheries Service wildlife biologist.
Would-be rescuers aboard the flotilla of 19 boats began the day early Wednesday by banging steel pipes in hopes of herding the mother and calf past the Rio Vista Bridge.
The goal was to prod the whales down to Antioch, where the Sacramento-San Joaquin River Delta joins the backwaters of San Francisco Bay.
At one point during the morning, the boats pushed the whales within about 100 yards of the bridge. But instead of passing under the span, the whales turned tail, diving under the pipe-banging fleet and back up river.
Authorities arranged to raise the bridge the next time the pair approached, reasoning that the noise and vibration of vehicles passing overhead might be spooking the animals.
But the whales refused to get near again. With the tide turning, rescuers suspended their efforts to reassess the situation, then resumed later in the day with the orca recordings.
Nothing budged the pair, and by nightfall all operations ended.
Scientists say the whales almost certainly have not eaten anything since appearing in the delta waters May 13, but added that whales can fast for prolonged periods. The more immediate concern, officials said, was the wounds.
As they geared up to attempt the bolder tactics, scientists cautioned that the use of killer whale sounds has its risks. Killer whale recordings used during the nearly monthlong effort that freed Humphrey the humpback in 1985 might have contributed to that whale's repeated groundings in the delta.
Spradlin said rescuers would continue to proceed "as gently as possible, to coax them back to where they belong."
The pair continued Wednesday to exhibit the tail slapping that started Tuesday. Although biologists commonly consider such action a sign of stress, "it could be the mother is simply communicating with her calf," Cordaro said.