BREVARD COUNTY, Fla. -

Add bottlenose dolphins to this year’s list of species dying mysteriously in the Indian River Lagoon.

Researchers have documented 23 dead dolphins in the lagoon since Jan. 1, all but a few in Brevard County. That’s more than twice what researchers would expect, based on the death rate during the past decade.

“It’s especially scary now to be losing so many manatees, and now dolphins,” said Teresa Mazza, a biologist with the Hubbs-SeaWorld Research Institute, which gathers the carcasses for research purposes.

The lagoon has seen more than 90 mysterious manatee deaths in just over eight months and 250 dead pelicans in the past two months, with most in Brevard.

Most of the dead dolphin have been adult females. The bottlenose deaths have occurred from Titusville to Central Brevard.

“We have seen a few animals with shark bites,” Mazza said, adding that it’s not always clear whether those happened before the dolphin died. “There’s a chance we have sick, emaciated, dying animals that could be falling prey to sharks.”

Hubbs is consulting with NOAA Fisheries Service to determine whether that federal agency will declare the dolphin die-offs an “unusual” event, opening up federal resources and launching its own investigation. The designation has already been made for the manatee die-off in the lagoon. NOAA is examining whether the two die-offs might be linked, Florida Today reports.

“Right now, we have a correlation in location, but we’re not seeing much else,” said Blair Mase, NOAA’s Southeast regional marine mammal stranding coordinator. “We’re monitoring the area very closely.”

An estimated 600 to 700 bottlenose dolphins live exclusively in the lagoon.

Tissue samples have been sent to a veterinary pathologist for testing, to look for heavy metals, contaminants and toxins.

“It could be any number of things,” Mazza said. “It’s not right in front of your face ... We’re getting animals that are emaciated. A few of the dolphins have been very skinny.”

Some have common skin lesions or empty stomachs.

“We haven’t really found a smoking gun, and a lot of times with unusual mortality events, you never do,” Mazza said.

The manatee and pelican body count also continues to climb.

The sea cows come in with digestive tracts full of thick algae, instead of seagrass. The pelicans are infested with parasites.

But the causes of those two die-offs also remain unknown.

Tests of the pelicans so far have come back negative for the West Nile virus, botulism and other pathogens, according to the Fish and Wildlife Research Institute in St. Petersburg.

The sea cows have been drowning, with signs of shock and intestinal problems. Their carcasses appear otherwise healthy, but their digestive tracts are filled with thick drift algae, also called macroalgae, and not much of their usual seagrass staple diet.

Seagrass has dwindled sharply, virtually vanishing in some portions of the lagoon, after a phytoplankton “superbloom” killed most of the plant in 2011.

Excess algae can grow when too many nutrients from fertilizer runoff, septic tanks, the atmosphere and other sources enter the estuary.

The St. Johns River Water Management District has embarked on a four-year initiative of increased monitoring, data collection, and field and lab work to figure out what went awry in the lagoon.

“You’re starting to see a lot less of everything, so there’s a lot of worry,” said Mike Badarack, who owns Space Coast Flyfishing Charters in Satellite Beach.

“The alligators aren’t touching them,” he said of the dead pelicans he’s seen. “The bird carcasses are just sitting there. Nothing’s eating them.”