So this is very easy. Once you find buoys (The only thing that makes this a achievement random) on a shipwreck or in crate. Just construct the fishing rod.
4 tips to make it super easy.
1. Shallow water.
2. Aim right at the fish. (Small fish are easiest!)
3. Don’t cast very far.
4. Once you have a fish on the line real it in as long as the water isn’t too deep to make your character swim just walk up to the bobber and boom fish is caught instead of fighting the fish.
Boom achievement unlocked!
**Repeat 10 times and you will get the 2nd achievement The Sea’s harvest!**