(05-23) 10:31 PDT RIO VISTA -- The humpback whales trapped in the Sacramento-San Joaquin Delta are still swimming around just north of the Rio Vista Bridge, where they have been since Sunday, and their health appears to be deteriorating.

Rescuers today repeated concerns that the mother and her calf are in jeopardy, and resumed their so-far unfruitful efforts to drive the giant marine mammals downstream toward the ocean. A veterinarian from the Marine Mammal Center in Sausalito who has been monitoring the whales has determined that gashes on both animals have actually opened up more over the past week-and-a-half.

Bernadette Fees, a spokeswoman with the state Department of Fish and Game, said rescuers began their attempts at 6:30 a.m. today, much earlier than in mornings past. Part of the goal of the early start time was to take advantage of the tides -- the whales have demonstrated a preference for swimming against the current. The winds are stiff today, but have so far not hampered rescue efforts, she said.

Fees said officials were "stepping up" efforts today to drive the whales, which are an endangered species, toward the Pacific Ocean, but wouldn't say what they would do differently.

For the past several days, officials have been placing a flotilla of about 12 boats north of the whales. Crews on the boats have been dangling pipes in the water and banging on them with hammers, creating an unpleasant sound for the sensitive creatures, but the whales have balked. They have either reversed direction or stopped heading south when they make it as far south as the Rio Vista Bridge.

The whales have been in freshwater for at least 11 days now.

Rescuers said Tuesday that they were beginning to get more concerned about the whales' health, noting that their wounds appear to have worsened since they first entered the Delta, and that their skin has become irregular and pitted.

Officials believe that the animals were injured when they were run over by a boat. On Monday, researchers took a tissue sample from the mother whale, which will help them determine her general health, nutritional status and where she is from.

The lab results, from Oregon State University, the University of Tennessee and the Northwest Fisheries Science Center in Seattle, are expected to take a week.

Fees said researchers do not belive traffic on the Rio Vista Bridge is the cause of the animal's problems there, noting that they have crossed under the span at least three times, both when it was closed to traffic and drawn up and when there were cars on it.

Fees said officials are continuing to enforce a 500-yard safety zone around the whales and encouraged mariners to tune to marine channel 1622A.

Some members of the rescue crews have been on the water for the past 10 days, she said, adding that the whales' safety remains a top priority for officials.

Fees said she does not know the total cost of the rescue effort but said that state, federal and local agencies are sharing the burden.

Jim Oswald, a spokesman for the Marine Mammal Center, said rescuers are fairly stumped.

"I haven't heard that the pipes have been successful," he said. "At end of the day it's up to the animals, but we will assist them any way we can. But remember, these are very large animals and it is difficult to work with them. That being said, we want to utilize every resource we have to work with them."

Officials have set up an e-mail address, sacramento.whales@noaa.gov, where members of the public can send their comments or recommendations for the rescue.

E-mail the writers at glenmartin@sfchronicle.com and mlagos@sfchronicle.com.