7. SOUNDBITE (English): Frances Gullandat, Marine Mammal Centre Director of Veterinary Science:
"We all hope it's going to work. We all have to be confident it will work and instill confidence in each other. But as Pieter Folkens (Alaska Whale Foundation biologist) said earlier, we have no experience of working with a mother and calf humpback this far inland and they do have injuries."
8. Wide of whales swimming
9. Mid of people watching whales from shore
10. Close-up of woman with binoculars
11. Whale swimming
12. Wide of US Coast Guard boat
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13. Various of Coast Guard boats
14. SOUNDBITE (English) Lesanne Lindborg, San Francisco resident:
"Everybody's wondering how on earth and why did they come up here and so we're all concerned and curious and baffled basically."
15. SOUNDBITE (English) Jessica Bravo, Elk Grove resident:
"I think it's nice that we get to see it but they need to go home for their health."
Biologists tried on Thursday to use recorded siren songs of humpback whales to lure an injured female and her wounded calf from a shipping channel and back towards the Pacific Ocean 90 miles (145 kilometres) away.
When the researchers played the underwater recordings from an 87-foot (26 metres)Coast Guard cutter, the whales swam away from the sound rather than toward it.
Hours later, the whales were still swimming at the Port of Sacramento, where they have been since Tuesday.
Scientists then decided to move the sound equipment to a 25-foot (7.6 metre) Coast Guard vessel, believing the noise from the larger ship's generator may have interfered with the whale sounds.
"We all hope it's going to work. We all have to be confident it will work and instill confidence in each other," Marine Mammal Centre veterinary science director Frances Gullandat said.
Gullandat and other experts say the latest situation is complicated because it involved a mother and calf rather than a single whale and the two whales were much farther into the delta than previous studies.
The injuries added another dimension, as scientists said they did not know how the wounds might affect the whales' behaviour.
The injuries were apparently caused by a boat propeller. Scientists checked them on Wednesday using photos of the animals swimming in the port.
The injury to the calf appears more severe than the mother's injury.
As hundreds of onlookers stood along the riverbank to watch the two mammals, San Francisco resident Lesanne Lindborg told reporters she was "baffled" by the whales unexpected trip to Sacramento.
"Everybody's wondering how on earth and why did they come up here and so we're all concerned and curious and baffled basically," Lindborg said.
Jessica Bravo from Elk Grove, California was watching the whales with her mother. The young girl said she loved seeing the animals but wanted them to "go home for their health."
It could take weeks to get the whales back where they belong, scientists said.
If the whales can be returned to their natural sea water habitat, which is cleaner than the fresh water in the port and where food is more plentiful, they probably won't need treatment, the researchers said.
Researchers think the pair had been on their northward migration from Mexico up the California coast when they were sidetracked and ended up in the lower Sacramento River.
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 autumn.