Click photo to enlarge
The Coast Guard and other boaters from various agencies try to block the way of the two wayward humpback whales. (Herman Bustamante Jr./Contra Costa Times)
RIO VISTA -- With scientists watching nearby, the wandering whales have been zigzagging all day within six miles of Ryer Island.

At one point the mother and calf traveled up and down a slough near the deep-river channel that they came down through on Sunday.

After letting the mammals rest all day, scientists are now talking about renewing rescue efforts on Friday.

Here's the latest from the scene:

3:30 p.m. Medical help will arrive soon

Unable to herd them or encourage them with sounds of any kind, rescuers announced today that they will try to hose them into moving down the river.

Frances Gulland, director of Veterinarian Services with the Marine Mammal Center of Sausalito, said during an afternoon briefing that they will borrow a fire boat from the city of Vallejo to help in their efforts.

Working with a hose aboard the fire boat, the rescuers will spray water near the animals in an attempt to prod them to safety.

Such hosing methods have never been tried before, and Gulland said no one knows whether it will work.

The marine experts are also working on a plan to administer antibiotics and possibly sedatives, if necessary, to the injured whales. Gulland said the rescuers still need to secure equipment and medicine, and that will take at least two days.

2:15 p.m.: Whales head farther north

The whales are now more than five miles north of the Ryer Island Ferry in heading back up river toward Sacramento. The mother and calf have headed up a tributary that parallels the deep water shipping channel past Liberty Island.

Rescuers and marine mammal experts will hold a news conference at 3:15 at the Rio Vista to update the situation.

10:30 a.m.: Whales head farther north

Although experts had planned to start herding the mammals this morning, they decided to change their tactics last night after trying to get the humpbacks on track using a new set of underwater sounds.

Wednesday was rescuers' biggest push to date with the acoustic techniques. Throughout the afternoon and into the evening, scientists used three different sounds, including those of a killer whale attacking a gray whale and her calf, humpbacks feeding in Monterey Bay, and computer-generated noises at various frequencies.

Bernadette Fees with the state Department of Fish and Game said yesterday's concerted efforts might have played into scientists' decision to cease all operations today.

"We don't want to desensitize them to these sounds," she said.

The whales were spotted about 7:15 this morning north of the Rio Vista Bridge, Fees said. They were last seen swimming just south of Ryer Island.

Two boats -- one in front and one behind whales -- will remain in the river today to enforce the 500-yard limit around the mammals. Scientists will keep watch from one or more boats nearby.

The massive mammals have been stranded in the Sacramento-San Joaquin Delta for going on two weeks.

Reach Rowena Coetsee at 925-779-7141 or rcoetsee@cctimes.com