There are many deep sea fishing outfits in the island, the best time seem to be between Oct and March, however you can go fishing pretty much year round depending on weather conditions.
Here are some outfits, call them and they should be able to tell you what to expect in May:
Just don't snag a giant Octopus and you should be fine.
Many places in PR but none are cheap, the above are just a few, some seem to go to the PR trench for Marlin.