This sound effect can be found on the Jurassic Dinosaurs Sound Effects Library, which was made by Sound Ideas. It's an extremely low pitched and slowed down variant of the 5th cry of Sound Ideas, DOLPHIN - VARIOUS, SEPARATE CRIES W/WAVE, ANIMAL from the Lucasfilm Sound Effects Library. Links: https://soundideas.sourceaudio.com/track/7559546 https://soundeffects.fandom.com/wiki/Sound_Ideas,_ANIMAL,_CALL_-_MOURNFUL_CRY_OR_WAIL_01#Audio_Samples