The Stuart fishermen, Robby Benz, Paul Peroulakis and Joe Asaro, said they were fishing at about 11:30 a.m. Sunday when they spotted a large mass in the water, TCPalm.com reported Tuesday.
The men brought their boat closer to investigate and discovered the carcass, estimated to weigh about 200 pounds, floating in the water.
The fishermen brought their discovery to Port Salerno's commercial fishing docks.
"I've never seen anything like it around here," Benz said. "That's why I took it to the commercial docks to see if any of the fishermen I knew there had ever seen one."
Benz said the commercial fishermen were as surprised at the discovery as he was, and he and his fellow fishermen contacted wildlife agencies to take custody of the carcass.
Ellie Van Os, director of education and exhibits for the Florida Oceanographic Society, said the men did a "really good job" of preserving the squid as "they recognized what they had."
"Anytime you get an animal from the depths like that it's very exciting," Van Os said.
Carli Segelson, a Florida Fish and Wildlife Conservation Commission spokeswoman, said the squid was analyzed briefly by the agency and handed off to a team from the University of Florida for further study.