Eleven of the dolphins were babies, IMMS director Moby Solangi tells The Sun Herald.
"In 2011, we had seen a spike in baby dolphins that died," he said. "Last year, things had stabilized and the numbers went down. Now we have another spike, and they're all occurring at the same time.
"This is a spike that we don't really understand. The ratio is unusual. We usually see a mix of males and females and different ages. These either were aborted or they died shortly after they were born."
He said dolphins don't normally begin giving birth until the end of February. The mothers swim closer to shore to give birth because the babies have to come up to the surface to take their first breath, Solangi said. Also, the shallow water is murky so sharks can't see them.
Birthing season runs from late February until April or May. Solangi said if the deaths had occurred after the normal birthing season began, he wouldn't be so concerned.
"Whether it's a human reason or a biological reason, we need to know," he said.
There are more dolphins off the coast of Mississippi, Louisiana and Alabama than any other place in the U.S. and that's why people here see them so often, Solangi said.
Solangi said he got a report last week that three dolphins were found dead near Horn Island, but when IMMS crews got there, they found only two. He received photos of all three and the one not found had its head removed.
"A dolphin with no head is unusual," he said. "Last year, we had people mutilating dolphins. We want people to know, because this is the birthing season, so they will see more animals closer to the shore."
IMMS workers performed necropsies, or autopsies, on the dolphins and sent tissue and culture samples to the National Oceanic and Atmospheric Administration to be analyzed.