April: the first mahi show up.
Spring proper. The current carries the first real waves of mahi past the Keys, the humps stay busy with tuna, and the weather turns friendly for everybody.
April is when the offshore report starts saying the word mahi again. Early pushes ride the current lines, and while the fish run smaller schools than summer's parade, the first gaffer of the year has a taste all its own.
The month keeps its winter manners too: blackfin still school the humps, straggler sailfish tail down the edge, and the reef is alive with yellowtail as the water warms. Seas average kinder than any month before it.
The sweet spot argument
April might be the year's best value: high-season variety, shoulder-season calendar space, and weather that lets the half day fish like something longer.
Quick answers
Are mahi around in April?
The first pushes, yes. It builds through the month; by late April the weed lines start meaning something.
Best trip length for April?
A half day covers the warming edge well. Add hours if you want to hunt current lines for the early mahi.
How is the weather?
One of the friendliest months: warming, drying, and calming, with none of summer's afternoon storm clockwork yet.