MELBOURNE, Fla. -

As the top mammal predator, bottlenose dolphins herald the overall health of the Indian River Lagoon — and our well being as well.

Those dolphins — which eat some of the same seafood we do — are dying at triple the usual rate, washing up gaunt and with other signs of long-term suffering, possibly from something they are eating, Local 6 News partner Florid Today reported.

“We’ve seen more dolphin deaths this year than we ever have in years past,” Wendy Noke Durden, a researcher at Hubbs-SeaWorld Research Institute told about a dozen Hubbs supporters and county officials Wednesday. “We’re almost three times what we’d expect.”

Since Jan. 1, at least 73 lagoon dolphins have died mysteriously, most within Brevard County.Biologists worry something might be awry with our local dolphins’ seafood diet, much of which we have in common.

But few answers have surfaced since July when scientists opened a formal federal investigation into the lagoon’s unusual dolphin deaths. More than half of similar marine mammal investigations yield no definitive cause. With more tissue tests pending, however, biologists hold out hope that answers will be forthcoming.

“We don’t have a smoking gun so far,” Noke Durden said.

One common thread: shrimp. Researchers have been finding the crustaceans in the guts of dead dolphins.

“I can tell you that’s not normal for a lot of our dolphins to have shrimp in their stomach,” said Megan Stolen, a research scientist at Hubbs.

Bottlenose dolphins in the lagoon prefer seatrout, black drum and other fish that make grunting sounds they can hear. But algae blooms that resulted in about a 60 percent loss of seagrass since 2009 have made those and other fish that rely on the grass beds harder to find.

No tests have found anything unusual in the lagoon shrimp, however, or other items in the dolphins’ guts, the researchers said.

Hubbs researchers say 662 bottlenose dolphins spend their lives almost exclusively in the lagoon. On average, 26 dolphins wash up dead or strand in the lagoon region annually, they said.

In July, NOAA Fisheries declared an Unusual Mortality Event due to the increased bottlenose dolphin deaths in the lagoon system.

The declaration frees up federal resources for a more in-depth investigation.

A separate bottlenose dolphin die-off this year in the mid-Atlantic prompted NOAA Fisheries to declare another “Unusual Mortality Event.” More than 800 dolphins have died or stranded this year in the Atlantic from New York to Virginia. More than nine times the historical average of bottlenose dolphins died or stranded in the mid-Atlantic region in July and August, alone.

The lagoon and mid-Atlantic unusual die-offs aren’t thought to be related, but scientists aren’t sure.

NOAA officials said in August that they suspect a measles-like virus, called morbillivirus, had killed or stranded the mid-Atlantic dolphins.

Federal scientists hope when mid-Atlantic dolphins migrate to the Indian River Lagoon region that lagoon dolphins will be immune.

But some biologists worry morbillivirus, the same pathogen that hammered the bottlenose dolphin population from New Jersey to Central Florida in the late 1980s, might follow a similar pattern, spreading to the lagoon region. The virus’ re-emergence here could inflict yet another blow to lagoon dolphins already under assault.

Studies show some lagoon dolphin have antibodies to morbillivirus, but it’s unknown whether that's enough to make them immune.

The telltale symptoms for morbillivirus — skin and oral lesions — have not been seen in the dead dolphins from the lagoon, Hubbs researchers said.

Dolphins aren’t alone in their deadly plight in the lagoon.

In April, NOAA formally declared the higher frequencies of manatees dying an unusual die-off. More than 115 manatees have perished in the lagoon from an unknown cause since July 2012. Federal and state biologists also are investigating the death of 250 to 300 brown pelicans this year.

The lagoon has had two other big dolphin die-offs in recent years: 41 dolphins in 2001 and 47 in 2008. What killed them remains a mystery.

About a decade ago, researchers first began discovering more viruses, fungal and bacterial lesions on lagoon bottlenose dolphins, and more conditions that dolphins and humans share, such as hepatitis, meningitis and cancer. Heart murmurs and cancer also began showing up for the first time in the species. Biologists suspect pollution is driving the higher incidence of those conditions.

The good news: this year’s dolphin deaths in the lagoon have tapered off in the past few months, Hubbs researchers said.

“We’re hopeful that perhaps the end is near,” Noke Durden said.