Sea creature

The sea creature (referred to as both whale and dolphin in the game files) is a creature found in the Commonwealth in 2287.

Characteristics
The creature appears to be a mutated aquatic species.

Biology
The creature likely derives from a species of dolphin that mutated after the Great War. Similarities with dolphins include: the beak, air hole, & a small dorsal fin. Intact specimens can be shot to cause the stomach to explode in a spectacular (and bloody) fashion.

Locations
Only carcasses of the creature can be found beached around the wasteland on boats, rivers and the coast. Another can be found deep underwater to the northeast of Fort Strong. Since the water can drown/irradiate most players before they can reach it, the Aquaboy perk is recommended when searching for it. The only instance of a living one is in the quest animation for the cut quest 20 Leagues Under the Sea.

Appearances
The sea creature only appears in Fallout 4.

Behind the scenes
The sea creature found on the boat west of Beantown Brewery is possibly a reference to the original Jaws film. On the boat, a skeleton with a blue jacket, blue bandanna, and a machete can be found with a dead sea creature nearby. The outfit clothing and machete are very similar to the ones worn and used by Quint in the original Jaws film, while the positioning of the sea creature matches that of where Jaws emerges and kills Quint.

If the player character swims underneath the boat, they will also find a diving cage resting on the river bed — another possible reference to Jaws.