My favorite way is to tame an Ichthy, Build a trap like the wyvern trap on the bottom close to their spawn, and using a high lvl Ichthy with high speed and stam, kite it right to the trap. The rest is simple.
Center tip: as they have added the mosa to the center I've found the easiest way to knock one out is find one close to the bubbles get its Agro and swim in the bubble the mosa will get stuck and it can't hit you. Also this gives you unlimited oxygen and sanctuary from being attacked by anything else. ðŸ¤˜ðŸ¼