Derecha, a right whale, gave birth Saturday in the ocean off Vilano Beach five years after the only other recording of a live birth, the Jacksonville Times-Union reported.
The discovery of the whale shortly before she was about to calve was made within approximately 10 miles of the patch of ocean the Navy chose last year for constructing an undersea warfare range.
"It was near the box ... but drawing a line in the ocean is a difficult thing," said William McLellan, a University of North Carolina-Wilmington research associate in charge of the survey work being done with Duke University for the Navy.
Environmental advocates, some of whom have sued to halt the training range plans, said that ship traffic and sonar use at the location could harm the whales.
"The Navy needs to go back to square one and reconsider," said Sharon Young, the Humane Society of the United States' marine issues field director and a former marine scientist.
"The fact that there's a birth was something a little unexpected. We all agree it's a good thing," said Jene Nissen, the training program manager.
Right whales from New England and Canada migrate each winter to the Florida-Georgia coast, which is the only known calving ground for the endangered whales, the newspaper reported. Of a total population of approximately 450, more than 100 whales went to the area this winter.
The Navy plans an installation of hundreds of devices on the ocean floor that can track training involving ships, submarines, helicopters and planes during combat. Onshore trainers would use the equipment to give crews almost immediate analysis and feedback on their performance. Advocates of the plan say the system would allow crews to quickly learn from their mistakes.