Scientists will try spraying water near wayward whales

Scientists attempting to return two humpback whales to the ocean said they would try a new technique today: using a fireboat to spray water near the pair.

If the water attracts or repels the whales, they will use that in their efforts to move the animals back into salt water.

The team working to rescue the whales had said Thursday that it would give the animals a break for the long Memorial Day weekend -- while continuing to enforce a 500-yard no-boating zone around the mother and calf, which in recent days have holed up on a stretch of the Sacramento River north of Rio Vista.

But the team is concerned about the cetaceans’ health.

Scientists from state and federal wildlife agencies hit the water Thursday morning to get a closer look at the whales, which are suffering the effects of nearly two weeks away from their saltwater environment as well as wounds probably caused by a ship’s propeller.

Rescuers have tried an array of tactics to herd the humpbacks back to the saltier waters, where their wounds might better heal.

None of the pipe-banging or playing of recorded whale sounds has pushed the pair past the Rio Vista Bridge, a bustling delta auto artery that has become a formidable obstacle to their return to the sea.

Biologists said they had ceased the herding efforts for the time being, partly out of concern that the whales might become too accustomed to the recorded noises. “We don’t want to habituate them to these different techniques; we don’t want them to get used to it like background noise,” said Trevor Spradlin, a wildlife biologist with the National Marine Fisheries Service.

Thursday morning, just four boats hit the water, allowing biologists a chance to give the whales a closer once-over, including snapping photos of the wounds that will be compared with pictures taken when the whales were first spotted in the Sacramento-San Joaquin River Delta on May 13.

The Sacramento River’s waters carry a host of pathogens -- viruses, fungi and bacteria -- that the whales’ systems were not designed to ward off, Spradlin said, opening a door to potential infections that could further complicate rescue efforts.

Authorities have been asked about the rescue operation’s cost. They said they didn’t have numbers yet, but pointed out that humpbacks are an endangered species, with about 6,000 surviving in the North Pacific.

eric.bailey@latimes.com