Is it legal to fish in the ocean on St Maarten?

Yes, you can fish in the ocean on St Maarten but you can only fish as a resident not a tourist.

Can I go spearfishing on St Maarten?

It is illegal to fish with a speargun anywhere.

Are the laws for fishing on St Maarten (Dutch side) the same as on Saint Martin (French side)?

No they are not. We only educate the community about the Dutch laws and are not reliably informed about the French laws and regulations.
Always check with local law enforcement!