Officials have completed a necropsy on one of the dozens of leopard sharks found dead in Redwood Shores last month but aren't any closer to pinpointing the cause of the sudden die-off.

The necropsy performed by a California Department of Fish and Game pathologist found "inflammation, bleeding, and lesions in the brain, and hemorrhaging from the skin near vents." Bleeding was also detected around the female shark's internal organs.

Additional tests, such as a bacterial study and microscopic tissue analysis, may provide an answer, according to a statement released by Redwood City. Results could be available by the end of the week.

"The ... pathologist is not drawing any conclusions until more examinations and all tests are performed," the statement said.

About 50 leopard sharks have been found dead in Redwood Shores since mid-April, according to the city.

Hundreds of the creatures have washed up on the shores of other Bay Area communities in recent weeks, said Sean Van Sommeran, executive director of the Santa Cruz-based Pelagic Shark Research Foundation. They have been reported in Foster City, Tiburon and as far north as Marin, but the highest concentration has been in the waterways of Redwood City.

"I suspect we're only seeing a tiny fraction of what's going on," he said.

Van Sommeran called the Department of Fish and Game's necropsy results "startling." He suspects a change in water quality may be to blame, but there has been no evidence of a large toxic spill in the area.

Tests of the Redwood Shores lagoon waters have revealed nothing unusual, according to Redwood City spokesman Malcolm Smith. The city is paying for the additional tests to determine the cause of the die-off.

Redwood City resident Catherine Greer was one of the first people to discover the dead sharks. She and her 13-year-old son Lorenzo Fernandez were fishing April 18 at the Redwood Shores lagoon when they spotted several of the creatures beached.

"I was really concerned to see one dead shark on the side of the water," she said. "Then what really concerned me is when I saw many more."

Greer said she and her son tried to push some of the sharks back into the water, "and they'd swim right back, thrashing their heads against the shore ... as if they were trying to commit suicide."

"I go fishing with my son," Greer added. "I know what their normal behavior is like, and what I saw was generally alarming."

According to Van Sommeran, the slender-bodied leopard shark, which typically grows to about four feet long, is a "pretty resistant" species.

Email Bonnie Eslinger at beslinger@dailynewsgroup.com.