For me if you had to put a wildlife in the ocean, first its a good idea and second make it at 100%. I explain, you have multiple choice but the more simple is to associate the classic scheme of animal that we found in rust and associate them with”equivalent”.
-Chicken = Tuna, Salmon, stingray,crabs etc …
-Shoal of fish (Like that later when you gonna put fishing you can go on the ocean with your boat catch a lot of fish when you discover a shoal) (care of predator)
-deer/cerf : See lion / See elephant/ Turtle (imagine already a turtle armor )
-boar : Dolphin
Horses : manatee (imagine riding something like that would be so cool)
wolf : shark (all sort/variety but of course you have to choose only one : GREAT WHITE MF) (CAN ATTACK BOAT so force player to take care of it) (give you the possibility to craft SHARKHEAD when you farm it, hell yeah…)
Bear : Killer Whale (dangerous like the bear and can attack boat too)
Like the one before me said, adding bigger whale like a RARE animal (Albinos whale? Moby Dick haha?) that you can found and who give lot of animal fat and other ressources…
For the crocs maybe add it in the swamp specially..
With all that things ofc your experience in the ocean of rust will never be the same … (nobody gonna swim in the water again hahahah)
But one more things if you do that Put a HARPPON in the game buyable in fishing village or something like that .. maybe t1 harpoon only one ammo, you shoot and take a time to recharge because its a rope on the harppon (possibility to “grab” ?) and T2 like in the game called “Depth” : faster, easier to reload because the ammunition will depend on the number carried. Hope to see that coming