Veterinarians tracking two lost whales in a California river took skin swabs to find the cause of raised blotches on their hides and were trying to take breath samples.
Using a sponge attached to a long pole, researchers wiped skin cells from bumps resembling blisters or lesions on the mother and calf as efforts to prod the whales ocean-ward dragged into a third week.
The humpbacks' long exposure to fresh water has led to serious skin damage, biologists said, making them vulnerable to germs they would not face in their native saltwater habitat.
"We really need to try to get them back into a more appropriate environment so they can start healing," said Trevor Spradlin, a marine mammal biologist with the National Oceanic and Atmospheric Administration.
The bumps could be the result of an infection from a bacteria, virus or fungus, but scientists would not know for sure until they examine the skin cells under a microscope, Spradlin said.
Deep gashes in both whales - likely suffered from a run-in with a boat's keel - have also worsened rather than healed outside their ocean home. However, veterinarians believe antibiotics injected into both whales Saturday could slow the damage.
Scientists will not know for several days whether the medicine is having a positive effect, Spradlin said.
The two humpbacks were spotted Sunday in a Sacramento River tributary about 70 miles (113 kilometers) from the Pacific, where the pair have been circling for the last week.
The whales were first spotted in fresh water May 13 and drew large crowds to the Port of Sacramento before suddenly departing and swimming about 20 miles (32 kilometers) downriver to their current location.
In what rescuers described as a difficult maneuver, biologists were also trying to position a funnel at the end of a long pole over the whales' blowholes to capture exhalation vapor when they surface to breathe.
Testing the breath could help scientists get a better sense of the whales' nutritional health and show whether the calf is still nursing.
Scientists have said the whales are not in immediate danger of starvation despite a lack of the saltwater foods that make up their diet, since humpbacks typically do not eat until the summer feeding season.
"Whales are not people. They don't need three square meals a day," said Brian Gorman, a spokesman for NOAA.
The delta's murky waters have prevented rescuers from taking clear aerial photographs of the humpbacks, which has hindered efforts to estimate their size and age.
The calf is likely a large one-year-old or a small two-year old, Spradlin said. Rough estimates put the female at about 45 feet (13.7 meters) long and between 60,000 pounds (27,215 kilograms) and 70,000 pounds (31,752kilograms).
The whales, nicknamed Delta and Dawn, appeared to respond to Friday's effort to push them downriver by spraying them with fire hoses. Scientists planned to use three to five fire boats shooting streams of water Tuesday to drive the humpbacks at least 15 miles (24 kilometers) downriver, where saltier water could help their health improve.