Are you staying around Jaco for the whole trip? I'm familiar with fishing some areas of NW Costa Rica and have been to Jaco a bunch but haven't fished right around there. Feel free to email me if you've got some specific questions at lunkerlineside@yahoo.com
Look for birds working the surf and busting fish. A good bet is to make your way to a river mouth. The local guys like to handline at the river mouths mostly at high incoming tides. Also look for locals handlining, they ususally know where the fish congregate. If you get into some fish near some handliners, offer them some...they're trying to get dinner and will be very happy......keep the peace between locals and travelers.
good luck