Back when I was playing on easy I brought my op lvl 45 sarco into the water. 5 mins later... I brought my sarco back to the Meg I was taming (I play with my dad) I got off and turned around saw the monsters coming at me and I thought my sarco would destroy them. I was wrong. Me and my dad and the remaining baryonyx had to rush to shore before we died. Tips:

Baryonyx swipe attack only works in the water so just swipe these idiots and kill/run

Crossbow + stone arrow works in the water so while swimming backwards shoot em to bits.

The weird long sea cow (sos I don't remember it's name) is immune to these monsters!! rip for all the tames that died to this animal. Now I just kill those things on sight