Does a player rolling a 7 have to discard half their cards if they have more than 7?
Yes, every player, including yourself / the player who rolled the 7.
From the rules:

every player who has more than 7 resource cards must select half...

With SeaFarers, you can choose to move the pirate instead of moving the robber. But that's the only difference. The discard half applies either way.
The rules specify only the pirate/robber choice. Leaving it up to the reader to remember that there's also the discard. But for confirmation, see this blog post:

Rolling seven is the same as in the original Catan in that the player who rolls seven gets to move the robber, and can take a resource from any player effected [sic] by where they move it to. Additionally any player with seven or more cards in their hand still has to discard half of them (the lesser half in the case of an odd number, i.e. if I have 9 cards with a seven is rolled I must discard 4).