MERRITT ISLAND, Fla. -

Biologists removed three more dead bottlenose dolphins in the Indian River Lagoon on Monday, bringing this year’s total lagoon bottlenose body count to at least 30.

Staff from Hubbs-SeaWorld Research Institute performed onsite examinations of the three dolphins: two in Merritt Island and one in Rockledge.

At least 30 dolphins have died in the lagoon since Jan. 1, all but a few in Brevard, most near Merritt Island. That’s more than twice what would be expected, based on the death rate during the past decade, Local 6 News partner Florida Today reported.

The National Oceanic and Atmospheric Administration already has declared the 100 or so manatee deaths in the lagoon since mid-2012 an Marine Mammal Unusual Mortality Event. The declaration triggers NOAA’s own formal investigation. The federal agency is examining whether the dolphin and manatee deaths might be connected.

While the manatees die quickly, the dolphins show signs of a drawn-out syndrome. Most are found very thin, with enlarged spleens.

As many as 300 brown pelicans also have died in the lagoon region since February, maybe more. Those tested were negative for botulism and other common causes of bird death. They come in with heavy parasite counts.

About half the dolphins studied in the lagoon in the past decade suffer from some form of chronic infectious disease, suggesting compromised immune systems.

Researchers find levels of mercury -- a potent neurotoxin -- in the skin and blood of lagoon dolphins that are higher than in any other dolphins that have been studied. They also find high incidence of tumors, heart problems, cancer, stomach ulcers, skin lesions, genital herpes and other emerging ailments previously thought rare in dolphins.

Dolphins captured near Merritt Island, especially, test in poor health.

Researchers have pointed to water tainted by treated sewage and runoff as the possible cause.