At a last moment decision I am joining friends in Tonga on early Sept. Any recommendation for photography of whales (a first for me)? what type of lens and setup? Any technique tips?

I have an Olympus/OM setup, with either 8mm fisheye or 7-14 pro + 180mm dome, or 12-50 kit + WWL1

Thanks!

The WWL is probably not an ideal choice as you will be snorkeling a lot. Since you don't dive deep it can be a problem with bubbles between the port glass. They clear out if you dive past 3-4 meters but you will splash and shoot on the surface quite often.

A fisheye with zoom ability is ideal in my opinion. I did very well with my 15mm fisheye in MagBay with humpbacks, but would have been nice to have more reach. If i get another chance i would add a 1.4tc to get more reach for when subjects are a bit further than point blank.