Harvest whale
From Halopedia, the Halo wiki
The Harvest Whale was a marine animal native to the UNSC colony of Harvest.
Appearence
It is rather more eel-like in appearance than Earth whales, and is unlikely to be related to Earth's mammalian variants.
History
When Harvest was glassed, the human population suffered tremendous losses, but the natural environment fared little better. The entire ecosystem was turned to a toxic environment, leading many native species to die off or be slaughtered by the open toxic air. The Harvest Whales suffered such a fate. The fate of the Harvest Whales and the animals on the planet Harvest is unknown, though most likely dead due to the environment.
It is unknown whether this animal will be seen alive in game, or merely dead. But very likely by the end of the Human-Covenant War, this species was extinct.