I was in Yelapa last April. The beach fishing opportunities are slim, particularly for fly fishing. The coastline is very rocky in most places. You can hike out to either point at the end of the cove and find promontories, but they're tough to work correctly. If the river is full, there might be some baby tarpon. I'm not sure what the precipitation has done so far this year. I'm guessing it's too low to fish.
I agree with D3Smartie. Go get a panga. There's guys who will greet you at the dock and ask to take you out. Some of them don't know what they're doing, but others have been doing it their whole life. Don't grab the first guy who approaches you. If the pangueros aren't around, ask down by the bars on the beach. Everybody knows a guy who knows a guy, etc. You can bargain. When I was there, I saw a boat that looked considerably better than the others in the bay, so I asked whose boat it was. After I got in touch with him, he came down from PV and picked us up the next morning.
When we got on the water, we found a ton of sierra, small tunas, and red snapper out by the islands. Some sizzling jacks made the day. Not too many mahi, though. We trolled a lone live bait for awhile by the islands and got a huge pickup (probably a rooster) but it kicked the hook. Ton of life last year. If you zero in on the flocks of birds you'll get those little skipjacks. Good luck.