About 900 dolphins and other large mammals, including porpoises and whales, have died in the northern Gulf of Mexico since December 2010. Some have linked the deaths to the Deepwater Horizon oil spill that began in April 2010, but litigation over the spill has limited the release of information about the causes of the deaths, Huelsenbeck said.

There have been no indications of harmful algae blooms in the Chesapeake or in the coastal bays west of Ocean City and Assateague Island, according to the Maryland Department of the Environment. Brevetoxins, neurotoxins emitted by algae blooms that can be deadly to mammals, have not been detected in Maryland this year, department spokeswoman Samantha Kappalman said.

Scientists are working to gather evidence before placing blame in the case of the dolphin deaths.

"They're collecting as much information as possible from all the stranding networks," Driscoll said. "Hopefully there is some more information on numbers from other states and some of causes."

It could be months or even years before an answer is found. Or a cause might never be determined: About half of the cases of mass marine mammal deaths that the National Oceanic and Atmospheric Administration deems "Unusual Mortality Events" remain unsolved.

It's also likely the number of deaths will grow, Huelsenbeck said.

He called the 120 deaths reported so far "the lowest-end estimate." He said the actual tally could number 1,000.

"This could have a more population-level impact that we don't know about yet," he said.

The state Department of Natural Resources asks anyone who finds a dead or stranded dolphin in Maryland to call (800) 628-9944.

Reuters contributed to this article.