In Saints Row 2, it only appears after following a series of arrows on island Secret Areas to the west of the map. After following the arrows, this creature rises from the water, although it does not move and does not attack Playa. It is an object, it behaves like other objects in the game and topples if knocked, sinking back into the water if it is shot or hit by a boat.
Go to Ruin Island - it is not necessary to have been to any other Secret Areas prior to this.
The large Cabbit is is located next to a Gang Operation on the south western boat in Port Pryor. It is caught around a fishing net. Unlike its Saints Row 2 counterpart, the Cabbit cannot be interacted with in any way.